diff --git a/packages/compiler/src/backend/executable-features.ts b/packages/compiler/src/backend/executable-features.ts
index 39756418e..dc2810c11 100644
--- a/packages/compiler/src/backend/executable-features.ts
+++ b/packages/compiler/src/backend/executable-features.ts
@@ -22,6 +22,7 @@ export function executableLinkFeatures(mod: IrModule, largePages = false): Nativ
     ...(features.stdioExtended ? { stdioExtended: true } : {}),
     ...(features.nodeIsland ? { nodeIsland: true } : {}),
     ...(features.moduleNamespace ? { moduleNamespace: true } : {}),
+    ...(features.moduleNamespaceDyn ? { moduleNamespaceDyn: true } : {}),
     zlib: features.zlib,
     ...(features.brotli ? { brotli: true } : {}),
     assert: features.assert,
diff --git a/packages/compiler/src/backend/llvm/lib-shared.ts b/packages/compiler/src/backend/llvm/lib-shared.ts
index e3e7e3797..aa2163476 100644
--- a/packages/compiler/src/backend/llvm/lib-shared.ts
+++ b/packages/compiler/src/backend/llvm/lib-shared.ts
@@ -306,6 +306,7 @@ export const LIB_FN_SYMS: Record<string, string> = {
   "process.builtinModule": "scr_process_builtin_module",
   "process.builtinUnsupported": "scr_process_builtin_unsupported",
   "module.namespaceValue": "scr_module_namespace_value",
+  "module.namespaceDyn": "scr_module_namespace_dyn_value",
   "fs.callbackValue": "scr_fs_callback_value",
   "fs.callbackCall": "scr_fs_callback_call",
   "process.hrtimeValue": "scr_process_hrtime_value",
@@ -1060,6 +1061,9 @@ export const LIB_FN_SYMS: Record<string, string> = {
   "nodeIsland.construct": "scr_node_island_construct",
   "nodeIsland.instanceof": "scr_node_island_instanceof",
   "nodeIsland.classMethods": "scr_node_island_class_methods",
+  "nodeIsland.share": "scr_node_island_share",
+  "nodeIsland.sharedTdz": "scr_node_island_shared_tdz",
+  "nodeIsland.classMethodsOf": "scr_node_island_class_methods_of",
   "nodeIsland.copyArrays": "scr_node_island_copy_arrays",
   "nodeIsland.awaitCopy": "scr_node_island_await_copy",
   "dyn.keySet": "scr_dyn_key_set",
diff --git a/packages/compiler/src/backend/native-link-info-core.ts b/packages/compiler/src/backend/native-link-info-core.ts
index 49681c986..6c282b74d 100644
--- a/packages/compiler/src/backend/native-link-info-core.ts
+++ b/packages/compiler/src/backend/native-link-info-core.ts
@@ -40,6 +40,9 @@ export interface NativeLinkFeatures {
   /** Module namespace objects as checked-dynamic values link
    * scr_module_namespace.c; absent (false) otherwise. */
   moduleNamespace?: boolean;
+  /** A module namespace boxed for typed code links
+   * scr_module_namespace_dyn.c; absent (false) otherwise. */
+  moduleNamespaceDyn?: boolean;
   zlib: boolean;
   /** node:zlib's Brotli forms: scr_brotli.c and the vendored brotli archive. */
   brotli?: boolean;
diff --git a/packages/compiler/src/backend/native/contracts.ts b/packages/compiler/src/backend/native/contracts.ts
index ba475be61..370bde77e 100644
--- a/packages/compiler/src/backend/native/contracts.ts
+++ b/packages/compiler/src/backend/native/contracts.ts
@@ -164,6 +164,9 @@ export interface CcOptions {
   /** Module namespace objects as checked-dynamic values: compiles
    * scr_module_namespace.c. */
   moduleNamespace?: boolean;
+  /** A module namespace boxed for typed code: compiles
+   * scr_module_namespace_dyn.c. */
+  moduleNamespaceDyn?: boolean;
   /** The program uses the process-events surface (signal/exit listeners,
    * stdin events, for-await over stdin — moduleUsesProcessEvents on the
    * IR): compiles scr_events.c into the binary. Event-free binaries keep
diff --git a/packages/compiler/src/backend/native/executable.ts b/packages/compiler/src/backend/native/executable.ts
index 439c528bb..8464f06d5 100644
--- a/packages/compiler/src/backend/native/executable.ts
+++ b/packages/compiler/src/backend/native/executable.ts
@@ -202,6 +202,8 @@ const RUNTIME_UNITS: readonly RuntimeUnit[] = [
   unit((u) => u.opts.wasm, "scr_wasm.c"),
   // Module namespace objects as checked-dynamic values.
   unit((u) => u.opts.moduleNamespace === true, "scr_module_namespace.c"),
+  // A module namespace as the frozen null-prototype object typed code sees.
+  unit((u) => u.opts.moduleNamespaceDyn === true, "scr_module_namespace_dyn.c"),
   unit(
     (u) =>
       u.opts.dynAsync ||
diff --git a/packages/compiler/src/backend/runtime-pack-core.ts b/packages/compiler/src/backend/runtime-pack-core.ts
index af4c9f874..a4884300c 100644
--- a/packages/compiler/src/backend/runtime-pack-core.ts
+++ b/packages/compiler/src/backend/runtime-pack-core.ts
@@ -103,6 +103,7 @@ export interface RuntimeFeatureSet extends NativeLinkFeatures {
   nodeIsland: boolean;
   brotli: boolean;
   moduleNamespace: boolean;
+  moduleNamespaceDyn: boolean;
   nativeFetch: boolean;
   abortSignalOnly: boolean;
   netEffective: boolean;
@@ -312,6 +313,7 @@ export function effectiveRuntimeFeatures(
     nodeIsland: features.nodeIsland === true,
     brotli: features.brotli === true,
     moduleNamespace: features.moduleNamespace === true,
+    moduleNamespaceDyn: features.moduleNamespaceDyn === true,
     nativeFetch,
     // The fetch unit has AbortController and AbortSignal; scr_abort.c is
     // the same implementation without the fetch transport.
diff --git a/packages/compiler/src/diagnostics/codes.ts b/packages/compiler/src/diagnostics/codes.ts
index 6461cf7ed..1e35903cd 100644
--- a/packages/compiler/src/diagnostics/codes.ts
+++ b/packages/compiler/src/diagnostics/codes.ts
@@ -116,6 +116,8 @@ export const DIAGNOSTIC_CODES = {
   SC8006: "Node island modules the build cannot collect",
   SC8010: "value crossing a Node island boundary in a form without an exact copy",
   SC8011: "native class extending a Node island class outside the supported forms",
+  SC8020: "stateful module duplicated across the Node island boundary",
+  SC8022: "island code extends a class of a compiled module",
   SC8030: "type patch: no range covers the installed copy",
   SC8031: "type patch: selector matches nothing",
   SC8032: "type patch: declaration already has the type",
@@ -154,9 +156,7 @@ export const RETIRED_DIAGNOSTIC_CODES = {
  * abandoned, delete them here. */
 export const RESERVED_DIAGNOSTIC_CODES = {
   SC8012: "Node islands (ni/* branches)",
-  SC8020: "Node islands (ni/* branches)",
   SC8021: "Node islands (ni/* branches)",
-  SC8022: "Node islands (ni/* branches)",
   SC8023: "Node islands (ni/* branches)",
 } as const satisfies Record<`SC${number}`, string>;
 
diff --git a/packages/compiler/src/diagnostics/diagnostic.ts b/packages/compiler/src/diagnostics/diagnostic.ts
index 6ee5ae159..ced3de029 100644
--- a/packages/compiler/src/diagnostics/diagnostic.ts
+++ b/packages/compiler/src/diagnostics/diagnostic.ts
@@ -348,6 +348,44 @@ export function nativeSubclassOfIslandDiag(loc: SrcLoc): ScrDiagnostic {
   };
 }
 
+/** SC8020 — a stateful module the program compiles is duplicated across
+ * the Node island boundary (an explicit "duplicate", or a form NI-6 cannot
+ * share yet): each side has its own state. */
+export function sharedModuleDuplicatedDiag(
+  module: string,
+  why: string,
+  loc: SrcLoc,
+): ScrDiagnostic {
+  return {
+    code: "SC8020",
+    message: `module '${module}' is duplicated across the Node island boundary although it is stateful: ${why}; the program and its islands each see their own copy`,
+    loc,
+    hint: 'remove "share": "duplicate" from its scriptc.packages entry to share one instance',
+  };
+}
+
+/** SC8022 — island code extends a class of a module the program compiles.
+ * A native instance cannot take an island subclass's overrides, so the
+ * module is not owned by the program: a package runs in Node for both
+ * sides (the build retries with it as a Node island); a program module is
+ * refused. */
+export function sharedClassExtendedDiag(
+  pkg: string | null,
+  file: string,
+  base: string,
+  loc: SrcLoc,
+): ScrDiagnostic {
+  return {
+    code: "SC8022",
+    message:
+      pkg !== null
+        ? `package '${pkg}' is shared with a Node island that extends its class '${base}': it runs in Node for both sides`
+        : `module '${file}' cannot be shared with a Node island that extends its class '${base}' (island subclasses of native classes)`,
+    loc,
+    hint: "move the subclass into the program, or mark the module as a Node island",
+  };
+}
+
 /** SC8002 — Node islands are off (or limited to marked islands) and an
  * npm package is outside the native subset. */
 export function nodeIslandsOffDiag(pkg: string, why: string, loc: SrcLoc): ScrDiagnostic {
diff --git a/packages/compiler/src/executable/executable-cache.ts b/packages/compiler/src/executable/executable-cache.ts
index f9fa04211..a1a322e48 100644
--- a/packages/compiler/src/executable/executable-cache.ts
+++ b/packages/compiler/src/executable/executable-cache.ts
@@ -67,6 +67,7 @@ export interface EarlyExecutableNativeFeatures {
   stdioExtended?: boolean;
   nodeIsland?: boolean;
   moduleNamespace?: boolean;
+  moduleNamespaceDyn?: boolean;
   zlib: boolean;
   brotli?: boolean;
   assert: boolean;
diff --git a/packages/compiler/src/frontend/lowering/expressions/identifiers.ts b/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
index 7ef9b9b0e..c73217ef8 100644
--- a/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
+++ b/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
@@ -700,8 +700,7 @@ export function lowerIdentifierExpr(lowerer: Lowerer, expr: ts.Identifier, loc:
   // String(NaN) is "NaN" in the number formatter; `NaN !== NaN` holds
   // because f64 compares are IEEE compares).
   if (expr.text === "Infinity" || expr.text === "NaN") {
-    const sym = lowerer.checker.getSymbolAtLocation(expr);
-    if (lowerer.isStdlibSymbol(sym)) {
+    if (lowerer.isStdlibGlobal(expr, expr.text)) {
       return { kind: "numLit", value: expr.text === "NaN" ? NaN : Infinity, type: F64, loc };
     }
   }
@@ -729,7 +728,7 @@ export function lowerIdentifierExpr(lowerer: Lowerer, expr: ts.Identifier, loc:
     return { kind: "libCall", fn: "dyn.arrayConstructor", args: [], type: DYN, loc };
   if (
     Object.values(BYTES_ELEMENT_NAME).includes(expr.text) &&
-    lowerer.isStdlibSymbol(lowerer.checker.getSymbolAtLocation(expr))
+    lowerer.isStdlibGlobal(expr, expr.text)
   ) {
     return {
       kind: "libCall",
diff --git a/packages/compiler/src/frontend/lowering/global-values.ts b/packages/compiler/src/frontend/lowering/global-values.ts
index 21593203d..91f705fef 100644
--- a/packages/compiler/src/frontend/lowering/global-values.ts
+++ b/packages/compiler/src/frontend/lowering/global-values.ts
@@ -16,6 +16,7 @@ import * as ts from "../ts7/adapter.js";
 import {
   BYTES_ELEMENT_NAME,
   DYN,
+  F64,
   STRING,
   UNDEFINED_T,
   type IrExpr,
@@ -133,6 +134,8 @@ export function jsGlobalValueByName(lowerer: Lowerer, name: string, loc: SrcLoc)
 /** jsGlobalValueByName for the globals other than the interned builtin
  * functions and constructors (builtinGlobalValue). */
 export function jsSpecialGlobalValue(lowerer: Lowerer, name: string, loc: SrcLoc): IrExpr | null {
+  if (name === "NaN" || name === "Infinity")
+    return { kind: "numLit", value: name === "NaN" ? NaN : Infinity, type: F64, loc };
   if (name === "String" || name === "Number" || name === "Boolean" || name === "BigInt")
     return primitiveCtorClosure(lowerer, name, loc, true);
   if (name === "ArrayBuffer")
diff --git a/packages/compiler/src/frontend/lowering/lower-modules.ts b/packages/compiler/src/frontend/lowering/lower-modules.ts
index 9804aebdf..df7c06def 100644
--- a/packages/compiler/src/frontend/lowering/lower-modules.ts
+++ b/packages/compiler/src/frontend/lowering/lower-modules.ts
@@ -16,6 +16,11 @@ import * as ts from "../ts7/adapter.js";
 import { collectRebindableFunctions, isRebindableFunction } from "./rebindable-functions.js";
 import { bindingSource } from "../binding-source.js";
 import type { Lowerer } from "./lowerer.js";
+import {
+  sharedInitFlagStores,
+  sharedModulePlans,
+  sharedModuleRegistrations,
+} from "./lower-shared-modules.js";
 import { dirname as dirnamePath, resolve as resolvePath } from "node:path";
 import { packageNameOfPath, probeNodeImportRefusal } from "../npm.js";
 import { isNpmStaticPackage } from "../npm-static.js";
@@ -3120,6 +3125,10 @@ export function lowerFileInit(
       });
     }
     if (sf === lowerer.entry) header.push(...lowerer.punycodeLinkWarning());
+    // Modules shared with Node islands register before any module runs
+    // (NI-6); the plan also creates their declarations' TDZ flags.
+    if (sharedModulePlans(lowerer).length > 0 && sf === lowerer.entry)
+      header.push(...sharedModuleRegistrations(lowerer));
     // A module that reads builtin globals through the global object by
     // computed names installs the program's lookup before its body runs.
     const computedGlobalRead = computedGlobalReadOf(lowerer, sf);
@@ -3381,6 +3390,7 @@ export function lowerFileInit(
         stmt,
         deferred ? [deferred] : lowerer.lowerStmts([stmt]),
       );
+      if (lowerer.sharedInitFlags.size > 0) stmtIr.push(...sharedInitFlagStores(lowerer, stmt));
       // Class EXPRESSIONS inside this statement queued their static
       // inits while it lowered: they land immediately before it — JS's
       // order for the supported whole-initializer positions.
diff --git a/packages/compiler/src/frontend/lowering/lower-node-island.ts b/packages/compiler/src/frontend/lowering/lower-node-island.ts
index 430bcb8d1..e48d482de 100644
--- a/packages/compiler/src/frontend/lowering/lower-node-island.ts
+++ b/packages/compiler/src/frontend/lowering/lower-node-island.ts
@@ -336,6 +336,16 @@ function islandLoadPath(lowerer: Lowerer, path: string, loc: SrcLoc): IrExpr {
   return literal;
 }
 
+/** The path literal of a module the program shares with its islands
+ * (lower-shared-modules.ts), named by its path in the shipped tree like a
+ * load's. */
+export function islandSharedPath(lowerer: Lowerer, path: string, loc: SrcLoc): IrExpr {
+  const literal: IrExpr & { kind: "strLit" } = { kind: "strLit", value: path, type: STRING, loc };
+  lowerer.nodeIslandModules.addProvided(path);
+  lowerer.nodeIslandLoads.push({ literal, path });
+  return literal;
+}
+
 function loadIslandModule(lowerer: Lowerer, path: string, loc: SrcLoc): IrExpr {
   return {
     kind: "libCall",
@@ -680,8 +690,27 @@ function withClassMethods(
   className: string,
   blame: ts.Node,
 ): IrExpr {
+  const builder = classMethodsBuilderOf(lowerer, className, blame, value.loc);
+  if (builder === null) return value;
+  return {
+    kind: "libCall",
+    fn: "nodeIsland.classMethods",
+    args: [value, builder],
+    type: DYN,
+    loc: value.loc,
+  };
+}
+
+/** The builder of a class's method table (a dyn closure answering
+ * {name: unbound method value}), or null for a class without methods. */
+function classMethodsBuilderOf(
+  lowerer: Lowerer,
+  className: string,
+  blame: ts.Node,
+  loc: SrcLoc,
+): IrExpr | null {
   const info = lowerer.classes.get(className);
-  if (info === undefined || info.def.runtime) return value;
+  if (info === undefined || info.def.runtime) return null;
   const names: string[] = [];
   for (
     let c: typeof info | undefined = info;
@@ -691,8 +720,7 @@ function withClassMethods(
     for (const m of c.def.methods ?? [])
       if (!names.includes(m) && islandMethodName(m)) names.push(m);
   }
-  if (names.length === 0) return value;
-  const loc = value.loc;
+  if (names.length === 0) return null;
   const builder = `%island.methods:${className}`;
   if (!lowerer.classMethodValueHelpers.has(builder)) {
     lowerer.classMethodValueHelpers.add(builder);
@@ -721,13 +749,75 @@ function withClassMethods(
     type: funcTypeFromParamShapes([], DYN),
     loc,
   };
-  return {
-    kind: "libCall",
-    fn: "nodeIsland.classMethods",
-    args: [value, lowerer.coerceToExpected(closure, DYN)],
-    type: DYN,
+  return lowerer.coerceToExpected(closure, DYN);
+}
+
+/** NI-6: the method-table builder of the class a shared module exports
+ * (`ident` is its declaration's name), or null. */
+export function classMethodsBuilder(
+  lowerer: Lowerer,
+  ident: ts.Identifier,
+  loc: SrcLoc,
+): IrExpr | null {
+  const decl = ident.parent;
+  if (decl === undefined || !ts.isClassDeclaration(decl)) return null;
+  return classMethodsBuilderOf(lowerer, lowerer.classNamer(decl), ident, loc);
+}
+
+/** NI-6: `new C(...)` from island code for the class a shared module
+ * exports: a function with the constructor's parameters (its dyn thunk
+ * checks the island's arguments) that constructs an instance, as a dyn
+ * closure, or null when the constructor's shape is not a plain list of
+ * parameters (the island's `new` then throws). */
+export function classConstructHelper(
+  lowerer: Lowerer,
+  ident: ts.Identifier,
+  loc: SrcLoc,
+): IrExpr | null {
+  const decl = ident.parent;
+  if (decl === undefined || !ts.isClassDeclaration(decl)) return null;
+  const className = lowerer.classNamer(decl);
+  const info = lowerer.classes.get(className);
+  if (info === undefined || info.def.runtime || info.localClass || info.generic) return null;
+  for (let c: typeof info | null = info; c; c = c.base) if (c.def.baseValueGlobal) return null;
+  if (lowerer.inheritsBuiltinErrorCtor(info)) return null;
+  const shapes = info.ctorParams;
+  if (shapes.some((s) => s.mode !== "required" && s.mode !== "omittable")) return null;
+  const name = `%island.new:${className}`;
+  if (!lowerer.classMethodValueHelpers.has(name)) {
+    lowerer.classMethodValueHelpers.add(name);
+    lowerer.noteEdge(`%${className}.constructor`);
+    const params = shapes.map((s, i) => ({ localId: `p${i}`, name: `p${i}`, type: s.type }));
+    const objectType: IrType = { kind: "object", className };
+    lowerer.liftedFns.push({
+      name,
+      params,
+      returnType: objectType,
+      locals: params.map((p) => ({ id: p.localId, name: p.name, type: p.type, mutable: false })),
+      body: [
+        {
+          kind: "return",
+          value: {
+            kind: "new",
+            className,
+            args: params.map((p) => varRef(p.localId, p.type, loc)),
+            type: objectType,
+            loc,
+          },
+          loc,
+        },
+      ],
+      loc,
+    });
+  }
+  const closure: IrExpr = {
+    kind: "closure",
+    fnName: name,
+    captures: [],
+    type: funcTypeFromParamShapes(shapes, { kind: "object", className }),
     loc,
   };
+  return lowerer.coerceToExpected(closure, DYN);
 }
 
 /** Native values NI-5 exports into the island by reference: functions,
diff --git a/packages/compiler/src/frontend/lowering/lower-shared-modules.ts b/packages/compiler/src/frontend/lowering/lower-shared-modules.ts
new file mode 100644
index 000000000..78d970d21
--- /dev/null
+++ b/packages/compiler/src/frontend/lowering/lower-shared-modules.ts
@@ -0,0 +1,602 @@
+/* Shared modules between the program and its Node islands (scope-B NI-6,
+ * DESIGN.md §2.6). A module the program compiles that island code also
+ * imports would otherwise exist twice, with two states. Rule: each module
+ * has exactly one owner.
+ *
+ *  - Program modules (user code): always shared, owned by the program.
+ *  - npm packages compiled natively and imported by island code: shared
+ *    when stateful (module-level state written after evaluation, exported
+ *    classes, evaluation effects), duplicated when pure (each side has its
+ *    own copy, which nobody can observe). `scriptc.packages.<name>.share`
+ *    ("shared" | "duplicate") overrides; duplicating a stateful package is
+ *    SC8020, a warning, because the two copies diverge.
+ *
+ * A shared module is registered at program start (nodeIsland.share, never
+ * loads Node) with its accessor: a generated function that answers the
+ * current values of its exports as a dyn array, the TDZ sentinel for a let
+ * or const whose declaration has not run yet (a flag the module's %init
+ * sets right after the declaration). The bootstrap's loader hooks
+ * (runtime scr_node_island_hooks.cjs) resolve island imports of the module
+ * to a generated ES module over those values.
+ *
+ * Island code is found syntactically: the files requireModule() loads and
+ * every JavaScript file of an island package, then the files they import
+ * that the program does not compile (Node's side of the closure). An
+ * import that resolves to a compiled module makes it a candidate. A
+ * specifier inside a comment or string can only add a candidate (an extra
+ * shared module), never lose one. */
+import { readdirSync, readFileSync, realpathSync, statSync } from "node:fs";
+import { resolveFrom } from "../../node-islands/resolve.js";
+import { join } from "node:path";
+import * as ts from "../ts7/adapter.js";
+import { locOf, isCjsJsFile } from "../program.js";
+import { PoisonError, newFnCtx, type Lowerer } from "./lowerer.js";
+import { BOOL, DYN, STRING, VOID, type IrExpr, type IrStmt, type SrcLoc } from "../../ir/ir.js";
+import { resolveBareModule } from "../resolve.js";
+import { packageDirOf } from "../../node-islands/origin.js";
+import { requireModuleSpecifiers, scanModuleSpecifiers } from "../../node-islands/modules.js";
+import { readProjectConfig } from "../../project-config.js";
+import {
+  sharedClassExtendedDiag,
+  sharedModuleDuplicatedDiag,
+} from "../../diagnostics/diagnostic.js";
+import {
+  classConstructHelper,
+  classMethodsBuilder,
+  islandSharedPath,
+} from "./lower-node-island.js";
+import { dynUndefinedExpr } from "../../ir/build.js";
+import { funcTypeFromParamShapes } from "./call-signatures.js";
+import { stripTypeWrappers } from "./typed-arguments.js";
+
+type ExportKind = "function" | "class" | "let" | "const" | "var";
+
+interface SharedExport {
+  name: string;
+  kind: ExportKind;
+  /** The declaration's name: its reference is the export's value. */
+  ident: ts.Identifier;
+  /** let/const: the flag global set after the declaration ran. */
+  flag?: string;
+}
+
+export interface SharedModulePlan {
+  sf: ts.SourceFile;
+  /** The real path Node resolves the module to. */
+  path: string;
+  exports: SharedExport[];
+}
+
+const MAX_ISLAND_FILES = 4000;
+
+function real(path: string): string {
+  try {
+    return realpathSync(path);
+  } catch {
+    return path;
+  }
+}
+
+function isJsFile(path: string): boolean {
+  return /\.(?:[cm]?js)$/.test(path);
+}
+
+/** The files `spec` may name from `from` (require and import conditions). */
+function resolveAll(from: string, spec: string): string[] {
+  if (spec.startsWith("node:")) return [];
+  const out = new Set<string>();
+  try {
+    out.add(real(resolveFrom(from, spec)));
+  } catch {
+    /* not resolvable for require */
+  }
+  if (!spec.startsWith(".") && !spec.startsWith("/")) {
+    for (const kind of ["import", "require"] as const) {
+      const js = resolveBareModule(from, spec, "js-only", kind);
+      if (js !== null) out.add(real(js.typesFile));
+    }
+  }
+  return [...out];
+}
+
+function packageJsFiles(dir: string, out: string[]): void {
+  let names: string[];
+  try {
+    names = readdirSync(dir);
+  } catch {
+    return;
+  }
+  for (const name of names) {
+    if (out.length >= MAX_ISLAND_FILES) return;
+    if (name === "node_modules" || name.startsWith(".")) continue;
+    const path = join(dir, name);
+    let isDirectory: boolean;
+    try {
+      isDirectory = statSync(path).isDirectory();
+    } catch {
+      continue;
+    }
+    if (isDirectory) packageJsFiles(path, out);
+    else if (isJsFile(name)) out.push(real(path));
+  }
+}
+
+function isExported(stmt: ts.Node): boolean {
+  const mods = ts.canHaveModifiers(stmt) ? ts.getModifiers(stmt) : undefined;
+  return mods?.some((m) => m.kind === ts.SyntaxKind.ExportKeyword) === true;
+}
+
+function isDefaultExport(stmt: ts.Node): boolean {
+  const mods = ts.canHaveModifiers(stmt) ? ts.getModifiers(stmt) : undefined;
+  return mods?.some((m) => m.kind === ts.SyntaxKind.DefaultKeyword) === true;
+}
+
+/** The top-level declarations of a module by name. */
+function localDeclarations(
+  sf: ts.SourceFile,
+): Map<string, { kind: ExportKind; ident: ts.Identifier }> {
+  const out = new Map<string, { kind: ExportKind; ident: ts.Identifier }>();
+  for (const stmt of sf.statements.nodes) {
+    if (ts.isFunctionDeclaration(stmt) && stmt.name && stmt.body)
+      out.set(stmt.name.text, { kind: "function", ident: stmt.name });
+    else if (ts.isClassDeclaration(stmt) && stmt.name)
+      out.set(stmt.name.text, { kind: "class", ident: stmt.name });
+    else if (ts.isVariableStatement(stmt)) {
+      const flags = stmt.declarationList.flags;
+      const kind: ExportKind =
+        (flags & ts.NodeFlags.Const) !== 0
+          ? "const"
+          : (flags & ts.NodeFlags.Let) !== 0
+            ? "let"
+            : "var";
+      for (const d of stmt.declarationList.declarations.nodes)
+        if (ts.isIdentifier(d.name)) out.set(d.name.text, { kind, ident: d.name });
+    }
+  }
+  return out;
+}
+
+/** The module's value exports (re-exports and default exports of
+ * expressions are not shared: NOTES.md shortcut). */
+function moduleExports(sf: ts.SourceFile): SharedExport[] {
+  const locals = localDeclarations(sf);
+  const out: SharedExport[] = [];
+  for (const stmt of sf.statements.nodes) {
+    if (ts.isExportDeclaration(stmt)) {
+      if (stmt.moduleSpecifier || stmt.isTypeOnly || !stmt.exportClause) continue;
+      if (!ts.isNamedExports(stmt.exportClause)) continue;
+      for (const el of stmt.exportClause.elements.nodes) {
+        if (el.isTypeOnly) continue;
+        const local = locals.get((el.propertyName ?? el.name).text);
+        if (local !== undefined) out.push({ name: el.name.text, ...local });
+      }
+      continue;
+    }
+    if (!isExported(stmt)) continue;
+    const def = isDefaultExport(stmt);
+    if (ts.isFunctionDeclaration(stmt) && stmt.name && stmt.body)
+      out.push({ name: def ? "default" : stmt.name.text, kind: "function", ident: stmt.name });
+    else if (ts.isClassDeclaration(stmt) && stmt.name)
+      out.push({ name: def ? "default" : stmt.name.text, kind: "class", ident: stmt.name });
+    else if (ts.isVariableStatement(stmt)) {
+      const flags = stmt.declarationList.flags;
+      const kind: ExportKind =
+        (flags & ts.NodeFlags.Const) !== 0
+          ? "const"
+          : (flags & ts.NodeFlags.Let) !== 0
+            ? "let"
+            : "var";
+      for (const d of stmt.declarationList.declarations.nodes)
+        if (ts.isIdentifier(d.name)) out.push({ name: d.name.text, kind, ident: d.name });
+    }
+  }
+  return out;
+}
+
+/** The name of a class imported from `spec` that the island file extends
+ * (`class X extends Base` or `extends ns.Base`), or null. */
+function extendedImport(text: string, spec: string): string | null {
+  const quoted = spec.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+  const names: string[] = [];
+  const named = new RegExp(
+    `import\\s*(?:(\\w+)\\s*,\\s*)?\\{([^}]*)\\}\\s*from\\s*["']${quoted}["']`,
+    "g",
+  );
+  for (const m of text.matchAll(named)) {
+    if (m[1] !== undefined) names.push(m[1]);
+    for (const part of m[2]!.split(",")) {
+      const local = part
+        .trim()
+        .split(/\s+as\s+/)
+        .at(-1)
+        ?.trim();
+      if (local) names.push(local);
+    }
+  }
+  const star = new RegExp(`import\\s*\\*\\s*as\\s+(\\w+)\\s*from\\s*["']${quoted}["']`, "g");
+  for (const m of text.matchAll(star)) names.push(`${m[1]!}\\.\\w+`);
+  const def = new RegExp(`import\\s+(\\w+)\\s+from\\s*["']${quoted}["']`, "g");
+  for (const m of text.matchAll(def)) names.push(m[1]!);
+  for (const name of names) {
+    const m = new RegExp(`\\bclass\\s+[\\w$]*\\s*extends\\s+(${name})\\b`).exec(text);
+    if (m !== null) return m[1]!;
+  }
+  return null;
+}
+
+const MUTATING_METHODS = new Set([
+  "set",
+  "add",
+  "delete",
+  "clear",
+  "push",
+  "pop",
+  "shift",
+  "unshift",
+  "splice",
+  "sort",
+  "reverse",
+  "fill",
+  "copyWithin",
+]);
+
+/** Why a module is stateful (one reason), or null when it is pure: no
+ * module-level binding reachable from its exports is written after
+ * evaluation, no exported class (its instances may cross or meet
+ * instanceof in island code), and no top-level effect beyond declarations. */
+/** Whether evaluating a module-level initializer runs no code: literals,
+ * names, functions and classes it creates, `require()` of a module (which
+ * is judged on its own), and object, array and operator expressions over
+ * those. */
+function inertInitializer(node: ts.Expression): boolean {
+  const e = stripTypeWrappers(node);
+  if (
+    ts.isIdentifier(e) ||
+    ts.isLiteralExpression(e) ||
+    ts.isNoSubstitutionTemplateLiteral(e) ||
+    ts.isArrowFunction(e) ||
+    ts.isFunctionExpression(e) ||
+    e.kind === ts.SyntaxKind.TrueKeyword ||
+    e.kind === ts.SyntaxKind.FalseKeyword ||
+    e.kind === ts.SyntaxKind.NullKeyword
+  )
+    return true;
+  if (ts.isClassExpression(e))
+    return !e.members.nodes.some(
+      (m) =>
+        ts.isClassStaticBlockDeclaration(m) ||
+        (ts.isPropertyDeclaration(m) &&
+          m.initializer !== undefined &&
+          !inertInitializer(m.initializer)),
+    );
+  if (ts.isParenthesizedExpression(e)) return inertInitializer(e.expression);
+  if (ts.isPrefixUnaryExpression(e))
+    return (
+      e.operator !== ts.SyntaxKind.PlusPlusToken &&
+      e.operator !== ts.SyntaxKind.MinusMinusToken &&
+      inertInitializer(e.operand)
+    );
+  if (ts.isBinaryExpression(e))
+    return (
+      !ts.isAssignmentOperator(e.operatorToken.kind) &&
+      e.operatorToken.kind !== ts.SyntaxKind.CommaToken &&
+      inertInitializer(e.left) &&
+      inertInitializer(e.right)
+    );
+  if (ts.isConditionalExpression(e))
+    return (
+      inertInitializer(e.condition) && inertInitializer(e.whenTrue) && inertInitializer(e.whenFalse)
+    );
+  if (ts.isArrayLiteralExpression(e))
+    return e.elements.nodes.every((el) => !ts.isSpreadElement(el) && inertInitializer(el));
+  if (ts.isObjectLiteralExpression(e))
+    return e.properties.nodes.every(
+      (p) =>
+        ts.isShorthandPropertyAssignment(p) ||
+        ts.isMethodDeclaration(p) ||
+        (ts.isPropertyAssignment(p) &&
+          !ts.isComputedPropertyName(p.name) &&
+          inertInitializer(p.initializer)),
+    );
+  if (ts.isCallExpression(e))
+    return (
+      ts.isIdentifier(e.expression) &&
+      e.expression.text === "require" &&
+      e.arguments.nodes.length === 1 &&
+      ts.isStringLiteralLike(e.arguments.nodes[0]!)
+    );
+  return false;
+}
+
+export function statefulReason(sf: ts.SourceFile): string | null {
+  const moduleLevel = new Map<string, string>(); // name -> kind
+  for (const stmt of sf.statements.nodes) {
+    if (ts.isClassDeclaration(stmt) && isExported(stmt))
+      return `it exports the class '${stmt.name?.text ?? "default"}'`;
+    if (ts.isVariableStatement(stmt)) {
+      const flags = stmt.declarationList.flags;
+      for (const d of stmt.declarationList.declarations.nodes) {
+        // A copy would run the initializer a second time.
+        if (d.initializer !== undefined && !inertInitializer(d.initializer))
+          return "its variable initializers run code";
+        if (!ts.isIdentifier(d.name)) continue;
+        if ((flags & ts.NodeFlags.Const) === 0) {
+          if (isExported(stmt)) return `it exports the mutable binding '${d.name.text}'`;
+          moduleLevel.set(d.name.text, "let");
+        } else {
+          moduleLevel.set(d.name.text, "const");
+        }
+      }
+      continue;
+    }
+    if (
+      ts.isFunctionDeclaration(stmt) ||
+      ts.isClassDeclaration(stmt) ||
+      ts.isImportDeclaration(stmt) ||
+      ts.isExportDeclaration(stmt) ||
+      ts.isInterfaceDeclaration(stmt) ||
+      ts.isTypeAliasDeclaration(stmt) ||
+      ts.isExportAssignment(stmt) ||
+      ts.isEmptyStatement(stmt)
+    )
+      continue;
+    if (ts.isExpressionStatement(stmt) && ts.isStringLiteral(stmt.expression)) continue; // directives
+    return "its evaluation has effects beyond declarations";
+  }
+  // Writes from function bodies to module-level bindings.
+  let reason: string | null = null;
+  const visit = (node: ts.Node, inFunction: boolean): void => {
+    if (reason !== null) return;
+    const fn = ts.isFunctionLike(node);
+    if (inFunction) {
+      if (ts.isBinaryExpression(node) && ts.isAssignmentOperator(node.operatorToken.kind)) {
+        let target: ts.Node = node.left;
+        while (ts.isPropertyAccessExpression(target) || ts.isElementAccessExpression(target))
+          target = target.expression;
+        if (ts.isIdentifier(target) && moduleLevel.has(target.text))
+          reason = `its function bodies write the module-level binding '${target.text}'`;
+      } else if (
+        (ts.isPrefixUnaryExpression(node) || ts.isPostfixUnaryExpression(node)) &&
+        (node.operator === ts.SyntaxKind.PlusPlusToken ||
+          node.operator === ts.SyntaxKind.MinusMinusToken) &&
+        ts.isIdentifier(node.operand) &&
+        moduleLevel.has(node.operand.text)
+      ) {
+        reason = `its function bodies write the module-level binding '${node.operand.text}'`;
+      } else if (
+        ts.isCallExpression(node) &&
+        ts.isPropertyAccessExpression(node.expression) &&
+        ts.isIdentifier(node.expression.expression) &&
+        moduleLevel.has(node.expression.expression.text) &&
+        MUTATING_METHODS.has(node.expression.name.text)
+      ) {
+        reason = `its function bodies mutate the module-level '${node.expression.expression.text}'`;
+      }
+    }
+    ts.forEachChild(node, (child) => visit(child, inFunction || fn));
+  };
+  visit(sf, false);
+  return reason;
+}
+
+/** The modules the program shares with its islands (computed once). */
+export function sharedModulePlans(lowerer: Lowerer): SharedModulePlan[] {
+  if (lowerer.sharedModules !== null) return lowerer.sharedModules;
+  const plans: SharedModulePlan[] = [];
+  lowerer.sharedModules = plans;
+  const compiled = new Map<string, ts.SourceFile>();
+  for (const sf of lowerer.moduleOrder) {
+    if (sf.isDeclarationFile) continue;
+    compiled.set(real(sf.fileName), sf);
+  }
+  // Island roots: requireModule() targets and island package files. A
+  // target the program compiles itself is loaded in Node as well: shared.
+  const queue: string[] = [];
+  const candidates = new Set<ts.SourceFile>();
+  for (const sf of lowerer.moduleOrder) {
+    const text = sf.text;
+    if (!text.includes("requireModule")) continue;
+    const from = real(sf.fileName);
+    for (const spec of requireModuleSpecifiers(text)) {
+      try {
+        const target = real(resolveFrom(from, spec));
+        const own = compiled.get(target);
+        if (own !== undefined) candidates.add(own);
+        else queue.push(target);
+      } catch {
+        /* lowering reports it */
+      }
+    }
+  }
+  for (const island of lowerer.nodeIslands?.packages.values() ?? [])
+    packageJsFiles(island.dir, queue);
+  if (queue.length === 0 && candidates.size === 0) return plans;
+  const seen = new Set<string>();
+  // Classes island code extends, by the compiled module that exports them.
+  const extended = new Map<ts.SourceFile, string>();
+  while (queue.length > 0 && seen.size < MAX_ISLAND_FILES) {
+    const file = queue.pop()!;
+    if (seen.has(file) || compiled.has(file) || !isJsFile(file)) continue;
+    seen.add(file);
+    let text: string;
+    try {
+      text = readFileSync(file, "utf8");
+    } catch {
+      continue;
+    }
+    // Specifiers in code only: a comment or a string that looks like an
+    // import names no module.
+    for (const spec of scanModuleSpecifiers(text).specifiers) {
+      for (const target of resolveAll(file, spec)) {
+        const sf = compiled.get(target);
+        if (sf !== undefined) {
+          candidates.add(sf);
+          const base = extendedImport(text, spec);
+          if (base !== null && !extended.has(sf)) extended.set(sf, base);
+        } else if (!seen.has(target)) queue.push(target);
+      }
+    }
+  }
+  if (candidates.size === 0) return plans;
+  const config = readProjectConfig(lowerer.entry.fileName);
+  for (const sf of lowerer.moduleOrder) {
+    if (!candidates.has(sf)) continue;
+    const path = real(sf.fileName);
+    const pkg = packageDirOf(path);
+    const loc: SrcLoc = { file: sf.fileName, start: 0, end: 0 };
+    const share = pkg === null ? "shared" : (config.packages.get(pkg.name)?.share ?? "auto");
+    const stateful = pkg === null ? "it is a program module" : statefulReason(sf);
+    const base = extended.get(sf);
+    if (base !== undefined) {
+      // Island code extends one of its classes: a native instance cannot
+      // take an island subclass's overrides, so the module cannot be owned
+      // by the program. A package then runs in Node for both sides
+      // (Node-owned, through handles; the build retries with it as an
+      // island); a program module is refused.
+      lowerer.pushDiag(sharedClassExtendedDiag(pkg?.name ?? null, sf.fileName, base, loc));
+      continue;
+    }
+    if (isCjsJsFile(sf, lowerer.program)) {
+      // Shortcut: CommonJS modules are not shared yet; each side keeps its
+      // copy, so a stateful one is reported.
+      if (stateful !== null)
+        lowerer.sharedModuleWarnings.push(
+          sharedModuleDuplicatedDiag(
+            pkg?.name ?? sf.fileName,
+            `${stateful}, and CommonJS modules cannot be shared yet`,
+            loc,
+          ),
+        );
+      continue;
+    }
+    if (share === "duplicate" || (share === "auto" && stateful === null)) {
+      if (stateful !== null)
+        lowerer.sharedModuleWarnings.push(
+          sharedModuleDuplicatedDiag(
+            pkg?.name ?? sf.fileName,
+            `${stateful}, and it is marked "share": "duplicate"`,
+            loc,
+          ),
+        );
+      continue;
+    }
+    const exports = moduleExports(sf);
+    for (const e of exports) {
+      if (e.kind !== "let" && e.kind !== "const") continue;
+      const flag = `%g.shared.${plans.length}.${e.name}%initialized`;
+      lowerer.globalsList.push({ id: flag, name: "%initialized", type: BOOL, mutable: true });
+      e.flag = flag;
+      let stmt: ts.Node | undefined = e.ident.parent;
+      while (stmt !== undefined && !ts.isVariableStatement(stmt)) stmt = stmt.parent;
+      if (stmt !== undefined) {
+        const list = lowerer.sharedInitFlags.get(stmt as ts.Statement) ?? [];
+        list.push(flag);
+        lowerer.sharedInitFlags.set(stmt as ts.Statement, list);
+      }
+    }
+    plans.push({ sf, path, exports });
+  }
+  if (plans.length > 0) lowerer.usesNodeIsland = true;
+  // Before island loads are lowered (the plans are computed in the first
+  // module's header): the module tree ships these as placeholders.
+  for (const plan of plans) lowerer.nodeIslandModules.addProvided(plan.path);
+  return plans;
+}
+
+/** The flag stores after a shared module's declaration statement. */
+export function sharedInitFlagStores(lowerer: Lowerer, stmt: ts.Statement): IrStmt[] {
+  const flags = lowerer.sharedInitFlags.get(stmt);
+  if (flags === undefined) return [];
+  const loc = locOf(stmt);
+  return flags.map((flag) => ({
+    kind: "assign",
+    localId: flag,
+    value: { kind: "boolLit", value: true, type: BOOL, loc },
+    loc,
+  }));
+}
+
+/** The registrations the entry's %init runs first: one nodeIsland.share
+ * per shared module, with its accessor. */
+export function sharedModuleRegistrations(lowerer: Lowerer): IrStmt[] {
+  const plans = sharedModulePlans(lowerer);
+  const out: IrStmt[] = [];
+  plans.forEach((plan, index) => {
+    const loc: SrcLoc = { file: plan.sf.fileName, start: 0, end: 0 };
+    const name = `%island.shared:${index}`;
+    const ctx = newFnCtx(false, null, null, DYN);
+    lowerer.fnStack.push(ctx);
+    const elems: IrExpr[] = [];
+    const kept: SharedExport[] = [];
+    try {
+      for (const e of plan.exports) {
+        let value: IrExpr;
+        try {
+          value = lowerer.coerceToExpected(lowerer.lowerExpr(e.ident), DYN);
+        } catch (error) {
+          if (!(error instanceof PoisonError)) throw error;
+          continue;
+        }
+        if (e.kind === "class") {
+          const builder = classMethodsBuilder(lowerer, e.ident, loc) ?? dynUndefinedExpr(loc);
+          const construct = classConstructHelper(lowerer, e.ident, loc) ?? dynUndefinedExpr(loc);
+          value = {
+            kind: "libCall",
+            fn: "nodeIsland.classMethodsOf",
+            args: [value, builder, construct],
+            type: DYN,
+            loc,
+          };
+        }
+        if (e.flag !== undefined) {
+          value = {
+            kind: "ternary",
+            cond: { kind: "varRef", localId: e.flag, type: BOOL, loc },
+            then: value,
+            else_: { kind: "libCall", fn: "nodeIsland.sharedTdz", args: [], type: DYN, loc },
+            type: DYN,
+            loc,
+          };
+        }
+        elems.push(value);
+        kept.push(e);
+      }
+    } finally {
+      lowerer.fnStack.pop();
+    }
+    lowerer.liftedFns.push({
+      name,
+      params: [],
+      returnType: DYN,
+      locals: ctx.locals,
+      body: [{ kind: "return", value: { kind: "dynArrLit", elems, type: DYN, loc }, loc }],
+      loc,
+    });
+    const exportsJson = JSON.stringify(kept.map((e) => ({ name: e.name, kind: e.kind })));
+    out.push({
+      kind: "exprStmt",
+      expr: {
+        kind: "libCall",
+        fn: "nodeIsland.share",
+        args: [
+          islandSharedPath(lowerer, plan.path, loc),
+          { kind: "strLit", value: exportsJson, type: STRING, loc },
+          lowerer.coerceToExpected(
+            {
+              kind: "closure",
+              fnName: name,
+              captures: [],
+              type: funcTypeFromParamShapes([], DYN),
+              loc,
+            },
+            DYN,
+          ),
+        ],
+        type: VOID,
+        loc,
+      },
+      loc,
+    });
+  });
+  return out;
+}
diff --git a/packages/compiler/src/frontend/lowering/lowerer.ts b/packages/compiler/src/frontend/lowering/lowerer.ts
index 475fab7e7..bf9775049 100644
--- a/packages/compiler/src/frontend/lowering/lowerer.ts
+++ b/packages/compiler/src/frontend/lowering/lowerer.ts
@@ -41,7 +41,11 @@ import {
   type UnitEvents,
   type WaveHost,
 } from "./unit-journal.js";
-import { moduleNamespaceObject, moduleNamespaceValue } from "./module-namespace-elements.js";
+import {
+  moduleNamespaceDynValue,
+  moduleNamespaceObject,
+  moduleNamespaceValue,
+} from "./module-namespace-elements.js";
 import { keyedHelperName, moduleTagNumber, portableRelativePath } from "./stable-names.js";
 import { positionTag, StructuralPositions } from "./structural-positions.js";
 import {
@@ -201,6 +205,7 @@ import {
   captureContextBinding,
   declareContextLocal,
   declareContextThis,
+  newFnCtx,
   type FnCtx,
 } from "./function-context.js";
 import type { FrontendServices } from "../services.js";
@@ -1473,7 +1478,10 @@ function lowerToIrWithIslands(
   }
   // Divergence warnings over the program's own modules: computed once,
   // after lowering, from the same checker (never part of a failure).
-  const divergences = scanDivergences(resultLowerer, moduleOrder);
+  const divergences = [
+    ...scanDivergences(resultLowerer, moduleOrder),
+    ...resultLowerer.sharedModuleWarnings,
+  ];
   timing("divergence-scan", { found: divergences.length });
   if (divergences.length > 0) result = { ...result, divergences };
   // The performance warning (SC6101): likely-hot functions of the program
@@ -3636,6 +3644,11 @@ export class Lowerer {
   }[] = [];
   /** Each island module load's path literal, set to its tree path when lowering ends. */
   readonly nodeIslandLoads: { literal: IrExpr & { kind: "strLit" }; path: string }[] = [];
+  /** NI-6: the modules shared with Node islands (lower-shared-modules.ts),
+   * their SC8020 warnings, and the TDZ flags their declarations set. */
+  sharedModules: import("./lower-shared-modules.js").SharedModulePlan[] | null = null;
+  readonly sharedModuleWarnings: ScrDiagnostic[] = [];
+  readonly sharedInitFlags = new Map<ts.Statement, string[]>();
   /** Per-directory answers of experimental-import.ts's declaration-file test. */
   readonly experimentalFiles = new Map<string, boolean>();
   /** Interned LifetimeRegion.run helpers, by callback type key. */
@@ -4115,6 +4128,10 @@ export class Lowerer {
       setTable("freezableArrays", this.freezableArrays),
       checkedTable("moduleOrder", () => this.moduleOrder.length),
       checkedTable("diags", () => this.diags.length),
+      // The shared-module plan runs inside the first unit that lowers a
+      // module; a warning it adds is a diagnostic of that unit, so its count
+      // is journaled like `diags` (the plan itself is unjournaled).
+      checkedTable("sharedModuleWarnings", () => this.sharedModuleWarnings.length),
       // Node island call sites hold literals of the unit's IR that lowering's
       // end rewrites to module tree paths (nodeIslandRecord): a unit that adds
       // one lowers again rather than replaying a record.
@@ -4390,6 +4407,11 @@ export class Lowerer {
     "argumentCountSlots",
     "coercions.widenedReturnTypes",
     "packageFileMemo",
+    // The modules shared with the islands (NI-6): a pure function of the
+    // program's modules, computed once, and the TDZ flags its plan gives a
+    // statement.
+    "sharedModules",
+    "sharedInitFlags",
     "slotOriginMemo",
     "recordOriginMemo",
     "boundaryCastOrder",
@@ -5231,6 +5253,79 @@ export class Lowerer {
     return this.moduleOrder.find((sf) => tsgoPath(resolve(sf.fileName)) === path) ?? null;
   }
 
+  /** A module namespace taken as a checked-dynamic value (`const u: unknown
+   * = ns`, `take(ns)`): the runtime's namespace object — one per module,
+   * Node's sorted export keys, live reads through a compiled getter, and
+   * Node's read-only write errors — built by `moduleNamespaceDynValue`.
+   * `node:` builtins have no compiled source and no complete export table,
+   * so they keep their fence. */
+  moduleNamespaceDyn(ns: IrExpr & { type: IrType & { kind: "moduleNs" } }): IrExpr | null {
+    if (!ns.type.moduleId.startsWith("file:")) return null;
+    return moduleNamespaceDynValue(this, ns);
+  }
+
+  /** A `Promise<module namespace>` taken as `Promise<unknown>` (or as
+   * `unknown`): one lifted async mapper per module awaits the promise and
+   * answers the same namespace object a bare namespace value boxes to, so
+   * the settlement is Node's namespace while the value stays a promise.
+   * The import() promise reaches these slots alone, and the runtime's
+   * per-module namespace cache keeps `await mapped === await original`; a
+   * rejection propagates unchanged. */
+  moduleNamespacePromiseDynValue(
+    value: IrExpr & { type: IrType & { kind: "promise" } },
+  ): IrExpr | null {
+    const inner = value.type.inner;
+    if (inner.kind !== "moduleNs" || !inner.moduleId.startsWith("file:")) return null;
+    const loc = value.loc;
+    const name = `%module.promise:${inner.moduleId}`;
+    const promiseT: IrType & { kind: "promise" } = { kind: "promise", inner };
+    if (!this.liftedFns.some((fn) => fn.name === name)) {
+      const context = newFnCtx(false, null, null, DYN);
+      context.isAsync = true;
+      const previousClass = this.currentClass;
+      this.currentClass = null;
+      this.fnStack.push(context);
+      let namespace: IrExpr | null = null;
+      try {
+        const awaited: IrExpr & { type: IrType & { kind: "moduleNs" } } = {
+          kind: "awaitExpr",
+          value: varRef("promise", promiseT, loc),
+          type: inner,
+          loc,
+        };
+        namespace = moduleNamespaceDynValue(this, awaited);
+        if (namespace) {
+          const fn: IrFunction = {
+            name,
+            params: [{ localId: "promise", name: "promise", type: promiseT }],
+            returnType: DYN,
+            locals: [
+              { id: "promise", name: "promise", type: promiseT, mutable: false },
+              ...context.locals,
+            ],
+            body: [{ kind: "return", value: namespace, loc }],
+            async: true,
+            loc,
+          };
+          this.liftedFns.push(fn);
+        }
+      } finally {
+        this.fnStack.pop();
+        this.currentClass = previousClass;
+      }
+      // A namespace with no compiled source has no dynamic value: keep the
+      // promise unconverted so the destination's own fence reports it.
+      if (!namespace) return null;
+    }
+    return {
+      kind: "call",
+      callee: name,
+      args: [value],
+      type: { kind: "promise", inner: DYN },
+      loc,
+    };
+  }
+
   builtinErrorInfoOf(symbol: ts.Symbol | null | undefined): ClassInfo | null {
     return builtinErrorInfoOf(this, symbol);
   }
@@ -11985,6 +12080,21 @@ export class Lowerer {
       const result = this.coerceToExpected(expr.result, expected);
       return { ...expr, result, type: result.type };
     }
+    // A `Promise<module namespace>` widening into `Promise<unknown>`, or
+    // into an `unknown` slot: map the payload through the namespace's
+    // dynamic value (moduleNamespacePromiseDynValue). A destination that
+    // wants the namespace type itself keeps the promise unchanged; the
+    // union path reuses this through its single-promise-arm conversion.
+    if (
+      expr.type.kind === "promise" &&
+      expr.type.inner.kind === "moduleNs" &&
+      (expected.kind === "dyn" || (expected.kind === "promise" && expected.inner.kind === "dyn"))
+    ) {
+      const mapped = this.moduleNamespacePromiseDynValue(
+        expr as IrExpr & { type: IrType & { kind: "promise" } },
+      );
+      if (mapped) expr = mapped;
+    }
     // An instance of a class declared `extends Array` is its array (the
     // same object); an array slot of another element type converts it as
     // an array.
@@ -12132,6 +12242,16 @@ export class Lowerer {
         const object = moduleNamespaceObject(this, ns) ?? moduleNamespaceValue(this, ns);
         if (object) return object;
       }
+      // A TypeScript source's module namespace as an untyped value: the
+      // runtime's namespace object with live reads, Node's sorted keys and
+      // read-only writes. `node:` builtins have no compiled source or
+      // complete export table here and keep their fence below.
+      if (expr.type.kind === "moduleNs") {
+        const boxed = this.moduleNamespaceDyn(
+          expr as IrExpr & { type: IrType & { kind: "moduleNs" } },
+        );
+        if (boxed) return boxed;
+      }
       if (
         expr.type.kind === "moduleNs" &&
         expr.type.moduleId === "builtin:events" &&
diff --git a/packages/compiler/src/frontend/lowering/module-namespace-elements.ts b/packages/compiler/src/frontend/lowering/module-namespace-elements.ts
index 2c8e6a475..405d2af5f 100644
--- a/packages/compiler/src/frontend/lowering/module-namespace-elements.ts
+++ b/packages/compiler/src/frontend/lowering/module-namespace-elements.ts
@@ -4,6 +4,7 @@ import * as ts from "../ts7/adapter.js";
 import {
   DYN,
   STRING,
+  SYMBOL_T,
   type IrExpr,
   type IrFunction,
   type IrStmt,
@@ -173,28 +174,28 @@ export function moduleNamespaceObject(
   };
 }
 
-/** A module namespace taken as an untyped value whose exports a copy
- * cannot represent: a binding that can change after initialization (`let`,
- * `var`), or an export the copy cannot name. The value is the runtime's
- * namespace object (scr_module_namespace_value): one per module, whose
- * property reads call a compiled getter for the export's current value and
- * whose writes throw Node's TypeError. An export whose value has no
- * checked-dynamic form throws its fence when it is read, and listing the
- * object's keys or inspecting it throws the "not supported yet" error. */
-export function moduleNamespaceValue(
+/** The compiled getter behind a namespace object: one lifted function per
+ * module that answers an export's current value by name, plus the module's
+ * sorted export names. An export whose value has no checked-dynamic form
+ * throws its fence when it is read. */
+function moduleNamespaceGetter(
   lowerer: Lowerer,
   ns: IrExpr & { type: IrType & { kind: "moduleNs" } },
-): IrExpr | null {
+): { name: string; keys: string[] } | null {
   const source = lowerer.sourceFileOfModuleNamespace(ns.type);
   if (!source) return null;
   const symbol = lowerer.checker.getSymbolAtLocation(source);
   if (!symbol) return null;
-  const exports: { key: string; declaration: ts.Node | undefined }[] = [];
+  const exports: { key: string; declaration: ts.Node | undefined; symbol: ts.Symbol }[] = [];
   for (const exported of lowerer.checker.getExportsOfModule(symbol)) {
     const target =
       exported.flags & ts.SymbolFlags.Alias ? lowerer.checker.getAliasedSymbol(exported) : exported;
     if (!(target.flags & ts.SymbolFlags.Value)) continue;
-    exports.push({ key: ts.symbolName(exported), declaration: target.valueDeclaration });
+    exports.push({
+      key: ts.symbolName(exported),
+      declaration: target.valueDeclaration,
+      symbol: target,
+    });
   }
   exports.sort((a, b) => (a.key < b.key ? -1 : a.key > b.key ? 1 : 0));
   const name = `%module.namespace:${ns.type.moduleId}`;
@@ -206,24 +207,37 @@ export function moduleNamespaceValue(
     lowerer.fnStack.push(context);
     try {
       const body: IrStmt[] = [];
-      for (const { key, declaration } of exports) {
+      for (const { key, declaration, symbol: exportSymbol } of exports) {
         const node = declaration ?? source;
         const diagsBefore = lowerer.diags.length;
         let read: IrStmt[];
         try {
           const identifier = declaration?.name as ts.Node | undefined;
-          if (!identifier || !ts.isIdentifier(identifier)) {
-            lowerer.unsupported(
-              "SC1090",
-              node,
-              `reading the unnamed export '${key}' through a module namespace object`,
-            );
+          let value: IrExpr;
+          if (identifier && ts.isIdentifier(identifier)) {
+            value = lowerer.lowerExprExpecting(identifier, DYN);
+          } else {
+            // `export default <expression>` and the anonymous default
+            // class/function have no named binding to read. The module's
+            // pre-registered default global holds the value the export
+            // statement snapshotted — the same storage a default import
+            // reads — so the namespace property answers it instead of
+            // fencing. A default whose type has no checked-dynamic form
+            // still fails the coercion below and keeps its fence.
+            const storage = lowerer.globalsBySymbol.get(exportSymbol);
+            if (!storage) {
+              lowerer.unsupported(
+                "SC1090",
+                node,
+                `reading the unnamed export '${key}' through a module namespace object`,
+              );
+            }
+            value = lowerer.coerceToExpected(varRef(storage.id, storage.type, loc), DYN);
           }
-          const value = lowerer.lowerExprExpecting(identifier, DYN);
           if (value.type.kind !== "dyn") {
             lowerer.unsupported(
               "SC1101",
-              identifier,
+              identifier ?? node,
               `reading the export '${key}' ('${lowerer.fmt(value.type)}') through a module namespace object`,
             );
           }
@@ -263,6 +277,24 @@ export function moduleNamespaceValue(
       lowerer.currentClass = previousClass;
     }
   }
+  return { name, keys: exports.map(({ key }) => key) };
+}
+
+/** A module namespace taken as an untyped value whose exports a copy
+ * cannot represent: a binding that can change after initialization (`let`,
+ * `var`), or an export the copy cannot name. The value is the runtime's
+ * namespace object (scr_module_namespace_value): one per module, whose
+ * property reads call a compiled getter for the export's current value and
+ * whose writes throw Node's TypeError. An export whose value has no
+ * checked-dynamic form throws its fence when it is read, and listing the
+ * object's keys or inspecting it throws the "not supported yet" error. */
+export function moduleNamespaceValue(
+  lowerer: Lowerer,
+  ns: IrExpr & { type: IrType & { kind: "moduleNs" } },
+): IrExpr | null {
+  const getter = moduleNamespaceGetter(lowerer, ns);
+  if (!getter) return null;
+  const loc = ns.loc;
   const value: IrExpr = {
     kind: "libCall",
     fn: "module.namespaceValue",
@@ -270,13 +302,82 @@ export function moduleNamespaceValue(
       strLit(ns.type.moduleId, loc),
       {
         kind: "arrayLit",
-        elems: exports.map(({ key }) => strLit(key, loc)),
+        elems: getter.keys.map((key) => strLit(key, loc)),
         type: arrayOf(STRING),
         loc,
       },
       {
         kind: "dynFrom",
-        value: { kind: "closure", fnName: name, captures: [], type: funcOf([STRING], DYN), loc },
+        value: {
+          kind: "closure",
+          fnName: getter.name,
+          captures: [],
+          type: funcOf([STRING], DYN),
+          loc,
+        },
+        type: DYN,
+        loc,
+      },
+    ],
+    type: DYN,
+    loc,
+  };
+  if (ns.kind === "moduleNsRef") return value;
+  return {
+    kind: "seqExpr",
+    stmts: [{ kind: "exprStmt", expr: ns, loc }],
+    result: value,
+    type: DYN,
+    loc,
+  };
+}
+
+/** A module namespace boxed for typed code through a dynamic slot
+ * (`const u: unknown = ns`, `take(ns)`): Node's namespace object as
+ * scr_module_namespace_dyn.c builds it — one non-extensible null-prototype
+ * object per module whose own sorted export names are enumerable read-only
+ * accessors, whose `Symbol.toStringTag` is "Module", whose reads call the same
+ * compiled getter, and whose writes and coerces throw Node's TypeErrors. A
+ * `node:` builtin has no compiled export table, so it keeps its fence. */
+export function moduleNamespaceDynValue(
+  lowerer: Lowerer,
+  ns: IrExpr & { type: IrType & { kind: "moduleNs" } },
+): IrExpr | null {
+  const getter = moduleNamespaceGetter(lowerer, ns);
+  if (!getter) return null;
+  const loc = ns.loc;
+  const value: IrExpr = {
+    kind: "libCall",
+    fn: "module.namespaceDyn",
+    args: [
+      strLit(ns.type.moduleId, loc),
+      {
+        kind: "arrayLit",
+        elems: getter.keys.map((key) => strLit(key, loc)),
+        type: arrayOf(STRING),
+        loc,
+      },
+      {
+        kind: "dynFrom",
+        value: {
+          kind: "closure",
+          fnName: getter.name,
+          captures: [],
+          type: funcOf([STRING], DYN),
+          loc,
+        },
+        type: DYN,
+        loc,
+      },
+      {
+        kind: "dynFrom",
+        value: {
+          kind: "libCall",
+          fn: "sym.wellKnown",
+          args: [strLit("toStringTag", loc)],
+          type: SYMBOL_T,
+          loc,
+        },
         type: DYN,
         loc,
       },
diff --git a/packages/compiler/src/frontend/lowering/receiver-returns.ts b/packages/compiler/src/frontend/lowering/receiver-returns.ts
index 5e83f236a..d1c160d7f 100644
--- a/packages/compiler/src/frontend/lowering/receiver-returns.ts
+++ b/packages/compiler/src/frontend/lowering/receiver-returns.ts
@@ -7,8 +7,10 @@
  * (`%dyn.class.call.N`) that calls such a method already holds a capsule
  * of the same instance at its exact class: its receiver after
  * normalization. The helper now calls a copy of the method that returns
- * nothing and answers its own receiver, so the call boxes nothing. Other
- * callers (vtables, typed code, method values) keep the method itself. */
+ * nothing and answers its own receiver, so the call boxes nothing. A
+ * direct call whose result nothing reads calls the copy too. Other callers
+ * (vtables, method values, calls that use the result) keep the method
+ * itself. */
 import type { IrExpr, IrFunction, IrStmt } from "../../ir/ir.js";
 import { VOID } from "../../ir/ir.js";
 import { varRef } from "../../ir/build.js";
@@ -57,6 +59,20 @@ export function returnDispatchReceivers(lowerer: Lowerer, functions: IrFunction[
       ];
     }
   }
+  // A direct call whose result nothing reads (`builder.set(1);` in typed
+  // code) needs no capsule at all.
+  for (const fn of [...functions]) {
+    everyStmtList(fn.body, {
+      stmt: (s) => {
+        if (s.kind === "exprStmt" && s.expr.kind === "call") {
+          const copy = copyOf(s.expr.callee);
+          if (copy) s.expr = { ...s.expr, callee: copy.name, type: VOID };
+        }
+        return true;
+      },
+      expr: () => true,
+    });
+  }
 }
 
 /** The helper's receiver is assigned only by its normalization, so it is
diff --git a/packages/compiler/src/index.ts b/packages/compiler/src/index.ts
index 7f9566425..e46e69434 100644
--- a/packages/compiler/src/index.ts
+++ b/packages/compiler/src/index.ts
@@ -702,6 +702,7 @@ async function compileExecutableNative(
     ...(features.stdioExtended ? { stdioExtended: true } : {}),
     ...(features.nodeIsland ? { nodeIsland: true } : {}),
     ...(features.moduleNamespace ? { moduleNamespace: true } : {}),
+    ...(features.moduleNamespaceDyn ? { moduleNamespaceDyn: true } : {}),
     zlib: features.zlib,
     ...(features.brotli ? { brotli: true } : {}),
     assert: features.assert,
diff --git a/packages/compiler/src/ir/builtin-effects.ts b/packages/compiler/src/ir/builtin-effects.ts
index 050699bd4..98b2687f2 100644
--- a/packages/compiler/src/ir/builtin-effects.ts
+++ b/packages/compiler/src/ir/builtin-effects.ts
@@ -23,6 +23,7 @@ export const MAY_THROW_LIB_FNS: ReadonlySet<IrLibFn> = new Set([
   "nodeIsland.construct",
   "nodeIsland.instanceof",
   "nodeIsland.classMethods",
+  "nodeIsland.classMethodsOf",
   "nodeIsland.copyArrays",
   // Node's argument, cipher-name, IV, tag-length and key-length errors.
   "crypto.cipherNew",
diff --git a/packages/compiler/src/ir/builtin-signatures.ts b/packages/compiler/src/ir/builtin-signatures.ts
index bfb39cf16..958f35011 100644
--- a/packages/compiler/src/ir/builtin-signatures.ts
+++ b/packages/compiler/src/ir/builtin-signatures.ts
@@ -207,6 +207,14 @@ function buildLibFnSignatures() {
     /** NI-5: a class instance crossing into an island, with the builder of
      * its class's method table (run once per class). Answers the value. */
     "nodeIsland.classMethods": { argTypes: [DYN, DYN], result: DYN },
+    /** NI-6 shared modules: registers a module the program shares with its
+     * islands (real path, exports JSON, accessor); the TDZ sentinel an
+     * accessor answers; the method table and constructor helper of an
+     * exported class by its class value (either may be undefined; answers
+     * the class value). */
+    "nodeIsland.share": { argTypes: [STRING, STRING, DYN], result: VOID },
+    "nodeIsland.sharedTdz": { argTypes: [], result: DYN },
+    "nodeIsland.classMethodsOf": { argTypes: [DYN, DYN, DYN], result: DYN },
     /** Island arrays of copied values as copies (a result, or an awaited
      * promise's value). */
     "nodeIsland.copyArrays": { argTypes: [DYN], result: DYN },
@@ -3604,6 +3612,11 @@ function buildLibFnSignatures() {
      * (scr_module_namespace_value): the module id, its sorted export names
      * and the compiled getter. One object per module. Never throws. */
     "module.namespaceValue": { argTypes: [STRING, arrayOf(STRING), DYN], result: DYN },
+    /** A module namespace as typed code sees it through a dynamic slot
+     * (scr_module_namespace_dyn_value): the module id, its sorted export
+     * names, the compiled getter, and the Symbol.toStringTag key. Draws
+     * Node's frozen null-prototype object, one per module. Never throws. */
+    "module.namespaceDyn": { argTypes: [STRING, arrayOf(STRING), DYN, DYN], result: DYN },
     "fs.callbackValue": { argTypes: [STRING], result: DYN },
     "fs.callbackCall": { argTypes: [STRING, DYN], result: DYN },
     "process.hrtimeValue": { argTypes: [], result: DYN },
diff --git a/packages/compiler/src/ir/ir.ts b/packages/compiler/src/ir/ir.ts
index ce220275b..7200da6dd 100644
--- a/packages/compiler/src/ir/ir.ts
+++ b/packages/compiler/src/ir/ir.ts
@@ -1037,7 +1037,9 @@ export function isRefCounted(t: IrType): boolean {
  * Only the relative paths enter an executable. */
 export interface IrNodeIslandModules {
   root: string;
-  files: { path: string; size: number; sha256: string }[];
+  /** `placeholder`: a program module the islands share, shipped as
+   * providedModulePlaceholder (node-islands/modules.ts), not its source. */
+  files: { path: string; size: number; sha256: string; placeholder?: true }[];
   links: { path: string; target: string }[];
   /** Where the executable finds the tree: absent when it carries the tree
    * itself, else a `$ORIGIN/` path (`--libnode=beside`). */
diff --git a/packages/compiler/src/ir/runtime-features.ts b/packages/compiler/src/ir/runtime-features.ts
index 58fce50b6..ed97ca935 100644
--- a/packages/compiler/src/ir/runtime-features.ts
+++ b/packages/compiler/src/ir/runtime-features.ts
@@ -1197,6 +1197,8 @@ const RUNTIME_FEATURE_RULES = {
   /** Module namespace objects as checked-dynamic values
    * (scr_module_namespace.c). */
   moduleNamespace: rule({ fns: ["module.namespaceValue"] }),
+  /** A module namespace boxed for typed code (scr_module_namespace_dyn.c). */
+  moduleNamespaceDyn: rule({ fns: ["module.namespaceDyn"] }),
   /** The WebAssembly API (scr_wasm.c). */
   wasm: rule({ prefixes: ["wasm."] }),
   /** crypto.subtle importKey/sign/verify/digest and CryptoKey:
@@ -1296,6 +1298,7 @@ function noRuntimeFeatures(): RuntimeFeatures {
     urlIdna: false,
     stdioExtended: false,
     moduleNamespace: false,
+    moduleNamespaceDyn: false,
     stream: false,
     streamDyn: false,
     handleProps: false,
diff --git a/packages/compiler/src/native/sanitizer.test.ts b/packages/compiler/src/native/sanitizer.test.ts
index f66381659..1a1262490 100644
--- a/packages/compiler/src/native/sanitizer.test.ts
+++ b/packages/compiler/src/native/sanitizer.test.ts
@@ -34,6 +34,7 @@ const features = {
   nodeIsland: false,
   brotli: false,
   moduleNamespace: false,
+  moduleNamespaceDyn: false,
   regex: true,
   copying: false,
   textDecoderLegacy: false,
diff --git a/packages/compiler/src/node-islands/libnode.ts b/packages/compiler/src/node-islands/libnode.ts
index 0210ab51b..8e44652a1 100644
--- a/packages/compiler/src/node-islands/libnode.ts
+++ b/packages/compiler/src/node-islands/libnode.ts
@@ -41,7 +41,7 @@ import {
 export const NODE_ISLAND_MIN_NODE = "24.13.1";
 
 /** The bridge ABI this compiler's runtime speaks (scr_node_bridge.h). */
-export const NODE_BRIDGE_ABI = 6;
+export const NODE_BRIDGE_ABI = 7;
 
 /** The prefix of a recorded path relative to the executable's directory. */
 export const ORIGIN = "$ORIGIN/";
diff --git a/packages/compiler/src/node-islands/modules.test.ts b/packages/compiler/src/node-islands/modules.test.ts
index 6207f5809..2c0d8ec73 100644
--- a/packages/compiler/src/node-islands/modules.test.ts
+++ b/packages/compiler/src/node-islands/modules.test.ts
@@ -6,6 +6,7 @@ import {
   NodeIslandModuleCollector,
   nodeIslandManifest,
   readNodeIslandModules,
+  requireModuleSpecifiers,
   scanModuleSpecifiers,
 } from "./modules.js";
 
@@ -259,3 +260,53 @@ describe("the collected module tree", () => {
     expect(readNodeIslandModules(tree)).toBe(`${join(root, "m.cjs")} changed during the build`);
   });
 });
+
+describe("modules the program provides", () => {
+  test("a shared program module ships as a placeholder, not its source", () => {
+    const source = "// internal pricing rules\nexport const margin = 0.37;\n";
+    const root = project({
+      "src/main.ts": "",
+      "src/pricing.ts": source,
+      "src/plugin.mjs": "export const x = 1;",
+    });
+    const collector = new NodeIslandModuleCollector();
+    expect(collector.add(join(root, "src/main.ts"), "./plugin.mjs")).toBeNull();
+    collector.addProvided(join(root, "src/pricing.ts"));
+    const tree = collector.tree()!;
+    const entry = tree.files.find((f) => f.path.endsWith("pricing.ts"))!;
+    expect(entry.placeholder).toBe(true);
+    const data = readNodeIslandModules(tree);
+    if (typeof data === "string") throw new Error(data);
+    const shipped = new TextDecoder().decode(data);
+    expect(shipped).not.toContain("internal pricing rules");
+    expect(shipped).not.toContain("margin");
+    expect(shipped).toContain("export const x = 1;");
+  });
+
+  test("island code that imports a provided module ships neither its source nor its imports", () => {
+    const root = project({
+      "src/main.ts": "",
+      "src/plugin.mjs": 'import { y } from "./shared.mjs";\nexport const z = y;',
+      "src/shared.mjs": 'import { secret } from "./internal.mjs";\nexport const y = secret;',
+      "src/internal.mjs": "export const secret = 42;",
+    });
+    const collector = new NodeIslandModuleCollector();
+    collector.addProvided(join(root, "src/shared.mjs"));
+    expect(collector.add(join(root, "src/main.ts"), "./plugin.mjs")).toBeNull();
+    const files = collector.tree()!.files;
+    expect(files.find((f) => f.path.endsWith("shared.mjs"))!.placeholder).toBe(true);
+    expect(files.some((f) => f.path.endsWith("internal.mjs"))).toBe(false);
+  });
+
+  test("requireModule specifiers come from code, not comments or strings", () => {
+    expect(
+      requireModuleSpecifiers(`
+        // requireModule("./commented.mjs")
+        /* requireModule("./block.mjs") */
+        const s = 'requireModule("./in-string.mjs")';
+        const t = \`requireModule("./in-template.mjs")\`;
+        const p = requireModule("./plugin.mjs");
+      `),
+    ).toEqual(["./plugin.mjs"]);
+  });
+});
diff --git a/packages/compiler/src/node-islands/modules.ts b/packages/compiler/src/node-islands/modules.ts
index 4ed57a038..7fc5c46d7 100644
--- a/packages/compiler/src/node-islands/modules.ts
+++ b/packages/compiler/src/node-islands/modules.ts
@@ -172,8 +172,10 @@ export class NodeIslandModuleCollector {
   private readonly traced = new Set<string>();
   /** Real paths of the calling modules. */
   private readonly callers = new Set<string>();
-  /** Real paths of the files loads name (addLoaded). */
+  /** Real paths of the files loads name (addLoaded, addProvided). */
   private readonly loaded = new Set<string>();
+  /** Program modules whose source the program provides (addProvided). */
+  private readonly provided = new Set<string>();
 
   /** Collects the module `specifier` names from `caller` (a real path).
    * Returns null, or the reason the build cannot ship it. */
@@ -195,6 +197,23 @@ export class NodeIslandModuleCollector {
     return this.addModule(this.placed(file));
   }
 
+  /** Collects a module whose source the program provides (a shared module,
+   * runtime scr_node_island_hooks.cjs): Node still resolves it to its file,
+   * so its package is in the tree, or, for a program module, a placeholder
+   * at its path (providedModulePlaceholder): the program's source stays out
+   * of the executable. Island code that imports it loads the program's
+   * module too, so it is not traced either. */
+  addProvided(file: string): void {
+    this.loaded.add(file);
+    const at = packageDirOf(file);
+    if (at !== null) this.addPackage(at.dir);
+    else {
+      const placed = this.placed(file);
+      this.files.add(placed);
+      this.provided.add(placed);
+    }
+  }
+
   /** The collected tree, or null when no call loads a file. */
   tree(): NodeIslandModuleTree | null {
     if (this.files.size === 0 && this.links.size === 0) return null;
@@ -213,13 +232,15 @@ export class NodeIslandModuleCollector {
     if (outer >= 0) root = parts.slice(0, outer).join(sep) || sep;
     const files: NodeIslandModuleFile[] = [];
     for (const file of [...this.files].sort()) {
+      const path = portable(relative(root, file));
+      if (this.provided.has(file)) {
+        const bytes = providedModulePlaceholder(path);
+        files.push({ path, size: bytes.length, sha256: sha256(bytes), placeholder: true });
+        continue;
+      }
       const bytes = trackedReadBytes(file);
       if (bytes === null) continue;
-      files.push({
-        path: portable(relative(root, file)),
-        size: bytes.length,
-        sha256: sha256(bytes),
-      });
+      files.push({ path, size: bytes.length, sha256: sha256(bytes) });
     }
     const links: NodeIslandModuleLink[] = [...this.links]
       .sort(([a], [b]) => (a < b ? -1 : a > b ? 1 : 0))
@@ -295,6 +316,9 @@ export class NodeIslandModuleCollector {
     if (this.traced.has(file)) return null;
     this.traced.add(file);
     this.files.add(file);
+    // The program provides its source: island code never runs this file,
+    // so what it imports is not shipped for it.
+    if (this.provided.has(file)) return null;
     const scope = packageScope(dirname(file));
     if (scope !== null) this.files.add(scope);
     if (!TRACED.test(file)) return null;
@@ -566,6 +590,27 @@ export interface ModuleSpecifierScan {
   computed: { at: number; form: string }[];
 }
 
+/** The string-literal arguments of `requireModule(...)` calls in source
+ * code, comments and template text excluded. */
+export function requireModuleSpecifiers(text: string): string[] {
+  const tokens = moduleTokens(text);
+  const out: string[] = [];
+  for (let k = 0; k + 3 < tokens.length; k++) {
+    const [name, open, arg, close] = [tokens[k]!, tokens[k + 1]!, tokens[k + 2]!, tokens[k + 3]!];
+    if (
+      name.kind === "name" &&
+      name.value === "requireModule" &&
+      open.kind === "punct" &&
+      open.value === "(" &&
+      arg.kind === "string" &&
+      close.kind === "punct" &&
+      close.value === ")"
+    )
+      out.push(arg.value);
+  }
+  return out;
+}
+
 export function scanModuleSpecifiers(text: string): ModuleSpecifierScan {
   const tokens = moduleTokens(text);
   const specifiers: string[] = [];
@@ -678,6 +723,16 @@ export function scanModuleSpecifiers(text: string): ModuleSpecifierScan {
 
 /* ── shipping the tree ────────────────────────────────────────────────── */
 
+/** What the tree ships at the path of a program module the islands share:
+ * Node resolves the module to this file and the program's loader hooks
+ * answer its source (runtime scr_node_island_hooks.cjs), so the file holds
+ * none of the program's source. Evaluating it throws. */
+export function providedModulePlaceholder(path: string): Uint8Array {
+  return new TextEncoder().encode(
+    `throw new Error(${JSON.stringify(`${path} is provided by the compiled program`)});\n`,
+  );
+}
+
 /** The manifest the executable records (scr_node_island.c reads it):
  * `{"files":[[path,size,sha256],...],"links":[[path,target],...]}`. Its
  * SHA-256 names the tree. */
@@ -696,11 +751,13 @@ export function readNodeIslandModules(modules: IrNodeIslandModules): Uint8Array
   for (const file of modules.files) {
     const path = join(modules.root, ...file.path.split("/"));
     let bytes: Uint8Array;
-    try {
-      bytes = new Uint8Array(readFileSync(path));
-    } catch {
-      return `${path} was removed during the build`;
-    }
+    if (file.placeholder === true) bytes = providedModulePlaceholder(file.path);
+    else
+      try {
+        bytes = new Uint8Array(readFileSync(path));
+      } catch {
+        return `${path} was removed during the build`;
+      }
     if (bytes.length !== file.size || sha256(bytes) !== file.sha256)
       return `${path} changed during the build`;
     parts.push(bytes);
diff --git a/packages/compiler/src/node-islands/snapshot.ts b/packages/compiler/src/node-islands/snapshot.ts
index 8c2c25562..54352743a 100644
--- a/packages/compiler/src/node-islands/snapshot.ts
+++ b/packages/compiler/src/node-islands/snapshot.ts
@@ -312,7 +312,7 @@ globalThis.__scriptcNodeIsland = {
   },
   setTimer: noop, clearTimer: noop, refTimer: noop, refreshTimer: noop,
   setImmediate: noop, clearImmediate: noop, refImmediate: noop,
-  nextTick: noop, emit: noop, load: noop,
+  nextTick: noop, emit: noop, load: noop, sharedPush: noop,
 };
 const fnToString = Function.prototype.toString;
 const hasOwn = Object.prototype.hasOwnProperty;
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6850-node-island-shared-singleton/main.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6850-node-island-shared-singleton/main.mjs.json
new file mode 100644
index 000000000..cd8d0b677
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6850-node-island-shared-singleton/main.mjs.json
@@ -0,0 +1,8 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6850-node-island-shared-singleton/state.mjs",
+  "<repo>/tests/corpus/6850-node-island-shared-singleton/tally.mjs",
+  "<repo>/tests/corpus/6850-node-island-shared-singleton/main.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6851-node-island-shared-class/main.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6851-node-island-shared-class/main.mjs.json
new file mode 100644
index 000000000..d8980e1f1
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6851-node-island-shared-class/main.mjs.json
@@ -0,0 +1,7 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6851-node-island-shared-class/shapes.mjs",
+  "<repo>/tests/corpus/6851-node-island-shared-class/main.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6852-node-island-shared-cycle/main.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6852-node-island-shared-cycle/main.mjs.json
new file mode 100644
index 000000000..bcb9ef07d
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6852-node-island-shared-cycle/main.mjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6852-node-island-shared-cycle/main.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6853-node-island-shared-registry/main.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6853-node-island-shared-registry/main.mjs.json
new file mode 100644
index 000000000..4aac1857f
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6853-node-island-shared-registry/main.mjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6853-node-island-shared-registry/main.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6854-node-island-shared-registry-native/main.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6854-node-island-shared-registry-native/main.mjs.json
new file mode 100644
index 000000000..5f3f514d3
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6854-node-island-shared-registry-native/main.mjs.json
@@ -0,0 +1,7 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6854-node-island-shared-registry-native/registry.mjs",
+  "<repo>/tests/corpus/6854-node-island-shared-registry-native/main.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/8412-module-namespace-untyped/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/8412-module-namespace-untyped/main.ts.json
new file mode 100644
index 000000000..464e68307
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/8412-module-namespace-untyped/main.ts.json
@@ -0,0 +1,8 @@
+{
+ "order": [
+  "<repo>/tests/corpus/8412-module-namespace-untyped/mod.ts",
+  "<repo>/tests/corpus/8412-module-namespace-untyped/mod-default.ts",
+  "<repo>/tests/corpus/8412-module-namespace-untyped/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/dynamic-method-receiver-statements.mjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/dynamic-method-receiver-statements.mjs.json
new file mode 100644
index 000000000..97d131a90
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/dynamic-method-receiver-statements.mjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/dynamic-method-receiver-statements.mjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.cjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.cjs.json
new file mode 100644
index 000000000..1b3fb5b25
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.cjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/shorthand-builtin-values.cjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.ts.json
new file mode 100644
index 000000000..1f444c73d
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/shorthand-builtin-values.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/shorthand-builtin-values.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/libnode-common/bridge/scr_node_bridge.cc b/packages/libnode-common/bridge/scr_node_bridge.cc
index 61d822309..73b381bdd 100644
--- a/packages/libnode-common/bridge/scr_node_bridge.cc
+++ b/packages/libnode-common/bridge/scr_node_bridge.cc
@@ -70,6 +70,10 @@ Global<Function> g_set_timer, g_clear_timer, g_ref_timer, g_refresh_timer;
 Global<Function> g_set_immediate, g_clear_immediate, g_ref_immediate;
 Global<Function> g_next_tick, g_emit;
 Global<Function> g_load; // the bootstrap's module loader (NI-4)
+Global<Function> g_shared_push; // the loader hooks' binding updates (NI-6)
+void SharedTable(const FunctionCallbackInfo<Value> &info);
+void SharedGet(const FunctionCallbackInfo<Value> &info);
+void SharedTdz(const FunctionCallbackInfo<Value> &info);
 
 char *Copy(const std::string &text, size_t *len) {
   char *out = static_cast<char *>(std::malloc(text.size() + 1));
@@ -267,6 +271,9 @@ char *Start(const ScrNodeBridgeHost *host, const char *bootstrap, const char *ar
   SetMethod(context, native, "settle", Settle);
   SetMethod(context, native, "run", Run);
   SetMethod(context, native, "listen", Listen);
+  SetMethod(context, native, "sharedTable", SharedTable);
+  SetMethod(context, native, "sharedGet", SharedGet);
+  SetMethod(context, native, "sharedTdz", SharedTdz);
   SetMethod(context, native, "isExport", IsExport);
   global->Set(context, Utf8(isolate, "__scriptcNodeIslandHost"), native).Check();
   TryCatch try_catch(isolate);
@@ -300,7 +307,8 @@ char *Start(const ScrNodeBridgeHost *host, const char *bootstrap, const char *ar
       !TakeFunction(isolate, context, d, "refImmediate", &g_ref_immediate) ||
       !TakeFunction(isolate, context, d, "nextTick", &g_next_tick) ||
       !TakeFunction(isolate, context, d, "emit", &g_emit) ||
-      !TakeFunction(isolate, context, d, "load", &g_load))
+      !TakeFunction(isolate, context, d, "load", &g_load) ||
+      !TakeFunction(isolate, context, d, "sharedPush", &g_shared_push))
     return Copy("the Node island bootstrap left an incomplete dispatcher", nullptr);
   global->Delete(context, Utf8(isolate, "__scriptcNodeIsland")).FromMaybe(false);
   global->Delete(context, Utf8(isolate, "__scriptcNodeIslandHost")).FromMaybe(false);
@@ -638,7 +646,7 @@ void Stop() {
   DropAllExports();
   for (Global<Function> *fn :
        {&g_set_timer, &g_clear_timer, &g_ref_timer, &g_refresh_timer, &g_set_immediate,
-        &g_clear_immediate, &g_ref_immediate, &g_next_tick, &g_emit})
+        &g_clear_immediate, &g_ref_immediate, &g_next_tick, &g_emit, &g_shared_push})
     fn->Reset();
   isolate->Exit();
   delete g_locker;
@@ -909,6 +917,14 @@ void ExportCall(const FunctionCallbackInfo<Value> &info) {
   std::memset(&out, 0, sizeof out);
   int status;
   if (info.IsConstructCall()) {
+    // `class Sub extends NativeClass` in island code: the native instance
+    // cannot take the island prototype's overrides (NI-6 shortcut).
+    auto self = g_exports.find(id);
+    if (self != g_exports.end() && !info.NewTarget()->StrictEquals(self->second.Get(isolate))) {
+      isolate->ThrowException(v8::Exception::TypeError(Utf8(
+          isolate, "scriptc: island code cannot extend a native class of a shared module yet")));
+      return;
+    }
     status = g_host->export_construct(id, args.data(), args.size(), &out);
   } else {
     ScrNodeValue self;
@@ -920,6 +936,15 @@ void ExportCall(const FunctionCallbackInfo<Value> &info) {
   if (!result.IsEmpty()) info.GetReturnValue().Set(result);
 }
 
+void ExportHasInstance(const FunctionCallbackInfo<Value> &info) {
+  Isolate *isolate = info.GetIsolate();
+  Local<Context> context = isolate->GetCurrentContext();
+  HostCall scope;
+  ScrNodeValue v;
+  FromV8(isolate, context, info[0], &v);
+  info.GetReturnValue().Set(g_host->export_instance_of(ExportIdArg(info.Data()), &v) == 1);
+}
+
 uint32_t HolderId(Local<Object> holder) {
   if (holder->InternalFieldCount() < 1) return 0;
   return ExportIdArg(holder->GetInternalField(0).As<Value>());
@@ -1103,6 +1128,14 @@ Local<Value> ExportValue(Isolate *isolate, Local<Context> context, const ScrNode
     fn->SetName(in->u.exp.name != nullptr
                     ? FromWtf8(isolate, in->u.exp.name, in->u.exp.name_len)
                     : String::Empty(isolate));
+    if (in->flags & SCR_NVF_CONSTRUCTOR) {
+      // A native class: instanceof asks the runtime (NI-6).
+      fn->DefineOwnProperty(context, v8::Symbol::GetHasInstance(isolate),
+                            Function::New(context, ExportHasInstance, data, 1).ToLocalChecked(),
+                            static_cast<v8::PropertyAttribute>(v8::DontEnum | v8::DontDelete |
+                                                               v8::ReadOnly))
+          .Check();
+    }
     obj = fn;
   } else if (in->flags & SCR_NVF_PROMISE) {
     Local<v8::Promise::Resolver> resolver = v8::Promise::Resolver::New(context).ToLocalChecked();
@@ -1563,6 +1596,56 @@ void DropHandle(uint32_t h) {
   Drop(h);
 }
 
+// ── shared modules (NI-6) ──────────────────────────────────────────────
+// Natives of the loader hooks (scr_node_island_hooks.cjs): the table of
+// modules the program shares, the current value of one export, and the
+// exports still in their temporal dead zone.
+
+void SharedTable(const FunctionCallbackInfo<Value> &info) {
+  Isolate *isolate = info.GetIsolate();
+  HostCall scope;
+  ScrNodeValue out;
+  std::memset(&out, 0, sizeof out);
+  g_host->shared_table(&out);
+  info.GetReturnValue().Set(FromWtf8(isolate, out.u.str.data, out.u.str.len));
+}
+
+void SharedTdz(const FunctionCallbackInfo<Value> &info) {
+  Isolate *isolate = info.GetIsolate();
+  HostCall scope;
+  ScrNodeValue out;
+  std::memset(&out, 0, sizeof out);
+  g_host->shared_tdz(&out);
+  info.GetReturnValue().Set(FromWtf8(isolate, out.u.str.data, out.u.str.len));
+}
+
+// sharedGet(mod, slot, mode, tdz): the value, or `tdz` for a binding in its
+// temporal dead zone.
+void SharedGet(const FunctionCallbackInfo<Value> &info) {
+  Isolate *isolate = info.GetIsolate();
+  Local<Context> context = isolate->GetCurrentContext();
+  HostCall scope;
+  ScrNodeValue out;
+  std::memset(&out, 0, sizeof out);
+  int status = g_host->shared_get(Uint32Arg(info, 0), Uint32Arg(info, 1),
+                                  static_cast<int>(Uint32Arg(info, 2)), &out);
+  if (status == 3) {
+    info.GetReturnValue().Set(info[3]);
+    return;
+  }
+  Local<Value> result;
+  ThrowOrReturn(isolate, context, status, &out, &result);
+  if (!result.IsEmpty()) info.GetReturnValue().Set(result);
+}
+
+void SharedPush(uint32_t mod, uint32_t slot, const ScrNodeValue *value) {
+  Enter e;
+  Local<Value> argv[] = {Integer::NewFromUnsigned(e.isolate, mod),
+                         Integer::NewFromUnsigned(e.isolate, slot),
+                         ToV8(e.isolate, e.context, value)};
+  Helper(e, g_shared_push, 3, argv);
+}
+
 const ScrNodeBridge kBridge = {
     SCR_NODE_BRIDGE_ABI,
     NODE_VERSION_STRING,
@@ -1599,6 +1682,7 @@ const ScrNodeBridge kBridge = {
     DropHandle,
     LiveHandles,
     ExportSettle,
+    SharedPush,
 };
 
 }  // namespace
diff --git a/packages/libnode-common/smoke/smoke.c b/packages/libnode-common/smoke/smoke.c
index ea3a2e41f..21b35f0ed 100644
--- a/packages/libnode-common/smoke/smoke.c
+++ b/packages/libnode-common/smoke/smoke.c
@@ -46,7 +46,7 @@ static const char kBootstrap[] =
     "  },\n"
     "  setTimer() { return 0; }, clearTimer() {}, refTimer() {}, refreshTimer() {},\n"
     "  setImmediate() { return 0; }, clearImmediate() {}, refImmediate() {},\n"
-    "  nextTick() {}, emit() {}, load() {},\n"
+    "  nextTick() {}, emit() {}, load() {}, sharedPush() {},\n"
     "};\n";
 
 static double now_ms(void) {
diff --git a/packages/runtime-pack-common/runtime-pack-matrix.mjs b/packages/runtime-pack-common/runtime-pack-matrix.mjs
index 70d0dae16..e5f41472b 100644
--- a/packages/runtime-pack-common/runtime-pack-matrix.mjs
+++ b/packages/runtime-pack-common/runtime-pack-matrix.mjs
@@ -93,6 +93,8 @@ export const OPTIONAL_RUNTIME_SOURCES = [
   ["scr_perf_loop.c", "perfLoop"],
   // Module namespace objects as checked-dynamic values.
   ["scr_module_namespace.c", "moduleNamespace"],
+  // The same namespace as the frozen null-prototype object typed code sees.
+  ["scr_module_namespace_dyn.c", "moduleNamespaceDyn"],
   // Blob and File box their reads as dyn promises through scr_async_dyn.c.
   ["scr_blob.c", "dynAsync"],
   ["scr_zlib.c", "zlib"],
diff --git a/packages/runtime/src/scr_blob.h b/packages/runtime/src/scr_blob.h
index 0882e41b6..7c7893322 100644
--- a/packages/runtime/src/scr_blob.h
+++ b/packages/runtime/src/scr_blob.h
@@ -34,6 +34,13 @@ ScrDyn *scr_process_builtin_unsupported(ScrStr *id, ScrStr *member);
  * one handle per module `id`, whose reads call `getter` with the export
  * name when `keys` lists it. Borrows all three; +1 handle. */
 ScrDyn *scr_module_namespace_value(ScrStr *id, ScrArr *keys, ScrDyn *getter);
+/* A module namespace as checked-dynamic code sees it
+ * (scr_module_namespace_dyn.c): one non-extensible null-prototype object per
+ * module `id`, Node's sorted export names as enumerable read-only accessors
+ * whose getters call `getter` with the name, `Symbol.toStringTag` "Module"
+ * (the well-known symbol is `tag_key`), and Node's strict-mode write
+ * TypeErrors. Borrows all four; +1 object. */
+ScrDyn *scr_module_namespace_dyn_value(ScrStr *id, ScrArr *keys, ScrDyn *getter, ScrDyn *tag_key);
 ScrDyn *scr_global_native(ScrArr *known);
 ScrDyn *scr_global_native_init(ScrArr *known, ScrDyn *(*console_get)(void));
 ScrDyn *scr_console_native(void);
diff --git a/packages/runtime/src/scr_json.c b/packages/runtime/src/scr_json.c
index 76bce14a4..5363a64c7 100644
--- a/packages/runtime/src/scr_json.c
+++ b/packages/runtime/src/scr_json.c
@@ -2652,6 +2652,18 @@ ScrDyn *scr_dyn_get_prototype(ScrDyn *object) {
     return scr_dyn_object_prototype();
   }
   if (object == scr_builtin_array_prototype) return scr_dyn_object_prototype();
+#ifdef SCR_NODE_ISLANDS
+  /* An island object: its V8 prototype, through the __proto__ accessor
+   * (undefined for an object without Object.prototype: null). */
+  if (scr_ni_is_handle(object)) {
+    ScrDyn *proto = scr_ni_get_str(object, "__proto__", 9);
+    if (proto != NULL && proto->kind == SCR_DYN_UNDEF) {
+      scr_dyn_release(proto);
+      return scr_dyn_new_null();
+    }
+    return proto;
+  }
+#endif
   if (object->kind == SCR_DYN_NULL || object->kind == SCR_DYN_UNDEF) {
     static const char message[] = "Cannot convert undefined or null to object";
     scr_throw_error_msg(SCR_ERR_TYPE, message, sizeof message - 1);
diff --git a/packages/runtime/src/scr_module_namespace_dyn.c b/packages/runtime/src/scr_module_namespace_dyn.c
new file mode 100644
index 000000000..632a09905
--- /dev/null
+++ b/packages/runtime/src/scr_module_namespace_dyn.c
@@ -0,0 +1,143 @@
+/* Module namespace objects handed to typed code as checked-dynamic values.
+ *
+ * In Node a module namespace is a non-extensible null-prototype object whose
+ * own properties are the module's exports in sorted order, which are
+ * enumerable and read-only, whose Symbol.toStringTag is "Module", and whose
+ * ToPrimitive finds no method. Every generic dynamic operation —
+ * Object.keys/values/entries/getOwnPropertyNames, for-in, `in`,
+ * JSON.stringify, identity, member reads and calls — already handles that
+ * shape through scr_json.c's object
+ * dispatch, so this unit only builds the object and links only into programs
+ * that box a namespace.
+ *
+ * The exports stay live: each property is an accessor whose getter calls the
+ * compiled namespace getter with the export name (the same getter the
+ * JavaScript-source representation uses), and whose setter throws Node's
+ * strict-mode read-only TypeError. An unknown name is not a member, so the
+ * object's own not-extensible state answers Node's "Cannot add property".
+ * One object per module keeps its identity.
+ *
+ * Node models the exports as writable data properties on a sealed object, so
+ * Object.isFrozen answers false and Object.isSealed true. Live reads need
+ * accessors here, and the accessor shape cannot be sealed without also
+ * freezing: Object.isFrozen and Object.isExtensible answer as Node's do,
+ * Object.isSealed does not. */
+#include "scr_runtime.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct ScrModuleNamespaceDyn {
+  ScrStr *id;
+  ScrDyn *object; /* retained for the program's lifetime */
+  struct ScrModuleNamespaceDyn *next;
+} ScrModuleNamespaceDyn;
+
+static SCR_TL ScrModuleNamespaceDyn *scr_module_namespace_dyns;
+static SCR_TL bool scr_module_namespace_dyn_cleanup_registered;
+
+static void scr_module_namespace_dyn_cleanup(void) {
+  while (scr_module_namespace_dyns) {
+    ScrModuleNamespaceDyn *ns = scr_module_namespace_dyns;
+    scr_module_namespace_dyns = ns->next;
+    scr_str_release(ns->id);
+    scr_dyn_release(ns->object);
+    free(ns);
+  }
+}
+
+/* An export's current value: the compiled getter takes the export name as a
+ * dyn string and answers it +1. */
+static ScrDyn *scr_module_namespace_dyn_read(ScrClosure *clo, ScrDyn *const *args, size_t argc) {
+  (void)args;
+  (void)argc;
+  ScrDyn *getter = scr_box_get_ref(clo->caps[0]);
+  ScrDyn *name = scr_box_get_ref(clo->caps[1]);
+  ScrDyn *argument = scr_dyn_retain(name);
+  ScrDyn *value = scr_dyn_call(getter, &argument, 1, "module namespace export");
+  scr_dyn_release(argument);
+  scr_dyn_release(name);
+  scr_dyn_release(getter);
+  return value;
+}
+
+/* A namespace export is read-only: Node's strict-mode TypeError names the
+ * export and the namespace's [object Module] tag. */
+static ScrDyn *scr_module_namespace_dyn_write(ScrClosure *clo, ScrDyn *const *args, size_t argc) {
+  (void)args;
+  (void)argc;
+  ScrDyn *name = scr_box_get_ref(clo->caps[0]);
+  ScrJsonBuf text;
+  scr_jb_init(&text);
+  scr_jb_puts(&text, "Cannot assign to read only property '");
+  scr_jb_write(&text, name->v.str->data, name->v.str->len);
+  scr_jb_puts(&text, "' of object '[object Module]'");
+  ScrStr *message = scr_jb_finish(&text);
+  scr_throw_error_msg(SCR_ERR_TYPE, message->data, message->len);
+  scr_str_release(message);
+  scr_dyn_release(name);
+  return NULL;
+}
+
+/* `thunk` as a dynamic function over one or two captured dynamic values. */
+static ScrDyn *scr_module_namespace_dyn_fn(ScrDynThunk thunk, ScrDyn *first, ScrDyn *second) {
+  ScrClosure *closure = scr_closure_new(NULL, second ? 2 : 1);
+  closure->caps[0] = scr_box_new_obj(scr_dyn_retain_v, scr_dyn_release_v, scr_dyn_trace_v);
+  scr_box_set_ref(closure->caps[0], scr_dyn_retain(first));
+  if (second) {
+    closure->caps[1] = scr_box_new_obj(scr_dyn_retain_v, scr_dyn_release_v, scr_dyn_trace_v);
+    scr_box_set_ref(closure->caps[1], scr_dyn_retain(second));
+  }
+  return scr_dyn_new_func(closure, thunk, 0, "native:module namespace", "module namespace export");
+}
+
+/* The namespace object: null prototype, one enumerable read-only accessor per
+ * export in `keys` order, a non-writable Symbol.toStringTag of "Module", and
+ * not extensible. */
+static ScrDyn *scr_module_namespace_dyn_build(ScrArr *keys, ScrDyn *getter, ScrDyn *tag_key) {
+  ScrDyn *object = scr_dyn_new_obj_null_proto();
+  for (size_t i = 0; i < keys->len; i++) {
+    ScrStr *key = scr_arr_get_ref(keys, (double)i); /* +1 */
+    ScrDyn *name = scr_dyn_new_str(key);
+    ScrDyn *read = scr_module_namespace_dyn_fn(scr_module_namespace_dyn_read, getter, name);
+    ScrDyn *write = scr_module_namespace_dyn_fn(scr_module_namespace_dyn_write, name, NULL);
+    scr_dyn_obj_set_accessor(object, key->data, key->len, read, write);
+    scr_dyn_release(name);
+    scr_str_release(key);
+  }
+  ScrStr *tag = scr_str_new("Module", 6);
+  ScrDyn *descriptor = scr_dyn_new_obj();
+  scr_dyn_obj_set(descriptor, "value", 5, scr_dyn_new_str(tag));
+  scr_dyn_obj_set(descriptor, "writable", 8, scr_dyn_new_bool(false));
+  scr_dyn_obj_set(descriptor, "enumerable", 10, scr_dyn_new_bool(false));
+  scr_dyn_obj_set(descriptor, "configurable", 12, scr_dyn_new_bool(false));
+  scr_dyn_release(scr_dyn_define_property(object, tag_key, descriptor));
+  scr_str_release(tag);
+  scr_dyn_release(descriptor);
+  scr_dyn_release(scr_dyn_prevent_extensions(object));
+  if (scr_exc_pending()) {
+    /* The tag key is a well-known symbol, so this cannot fail in practice; a
+     * pending exception still must not be cached. */
+    scr_dyn_release(object);
+    return NULL;
+  }
+  return object;
+}
+
+ScrDyn *scr_module_namespace_dyn_value(ScrStr *id, ScrArr *keys, ScrDyn *getter, ScrDyn *tag_key) {
+  for (ScrModuleNamespaceDyn *ns = scr_module_namespace_dyns; ns; ns = ns->next) {
+    if (ns->id->len == id->len && memcmp(ns->id->data, id->data, id->len) == 0)
+      return scr_dyn_retain(ns->object);
+  }
+  if (!scr_module_namespace_dyn_cleanup_registered) {
+    scr_atexit(scr_module_namespace_dyn_cleanup);
+    scr_module_namespace_dyn_cleanup_registered = true;
+  }
+  ScrDyn *object = scr_module_namespace_dyn_build(keys, getter, tag_key);
+  if (!object) return NULL;
+  ScrModuleNamespaceDyn *ns = malloc(sizeof(*ns));
+  if (!ns) scr_trap("scriptc: out of memory\n");
+  *ns = (ScrModuleNamespaceDyn){ scr_str_retain(id), scr_dyn_retain(object), scr_module_namespace_dyns };
+  scr_module_namespace_dyns = ns;
+  return object;
+}
diff --git a/packages/runtime/src/scr_node_bridge.h b/packages/runtime/src/scr_node_bridge.h
index ca73792bb..674a9ff68 100644
--- a/packages/runtime/src/scr_node_bridge.h
+++ b/packages/runtime/src/scr_node_bridge.h
@@ -17,7 +17,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#define SCR_NODE_BRIDGE_ABI 6u
+#define SCR_NODE_BRIDGE_ABI 7u
 /* The symbol a bridge library exports: `const ScrNodeBridge *(void)`. */
 #define SCR_NODE_BRIDGE_ENTRY "scr_node_bridge_v1"
 
@@ -200,6 +200,24 @@ typedef struct ScrNodeBridgeHost {
   void (*export_watch)(uint32_t id);
   /* V8 collected the representative of `id`. */
   void (*export_release)(uint32_t id);
+  /* `value instanceof <export id>` for a native class representative
+   * (its Symbol.hasInstance): 1 or 0. */
+  int (*export_instance_of)(uint32_t id, const ScrNodeValue *value);
+  /* ── shared modules (NI-6): modules the program compiled that island
+   * code imports resolve, through the loader hooks of the bootstrap, to
+   * generated modules over the live native exports. ── */
+  /* The table, as SCR_NV_STRING JSON: [{"path","exports":[{"name","kind"}]}]
+   * (index = module id, export index = slot). */
+  void (*shared_table)(ScrNodeValue *out);
+  /* The current value of a shared export. mode 0: read; 1: read and bind
+   * (the generated module holds it: later native changes are pushed with
+   * bridge->shared_push); 2: bind late (the binding is in its temporal
+   * dead zone: it is pushed once the native declaration ran). 0: *out is
+   * the value; 1: threw (*out thrown); 3: in its temporal dead zone. */
+  int (*shared_get)(uint32_t mod, uint32_t slot, int mode, ScrNodeValue *out);
+  /* The exports in their temporal dead zone now, as SCR_NV_STRING JSON
+   * [[mod, slot], ...]. */
+  void (*shared_tdz)(ScrNodeValue *out);
 } ScrNodeBridgeHost;
 
 typedef struct ScrNodeBridge {
@@ -290,6 +308,9 @@ typedef struct ScrNodeBridge {
   uint32_t (*live_handles)(void);
   /* Settles the V8 promise representing native promise `id` (NI-5). */
   void (*export_settle)(uint32_t id, int rejected, const ScrNodeValue *value);
+  /* NI-6: the native value of shared export (mod, slot) changed: the
+   * generated module's binding takes `value`. */
+  void (*shared_push)(uint32_t mod, uint32_t slot, const ScrNodeValue *value);
 } ScrNodeBridge;
 
 #endif /* SCR_NODE_BRIDGE_H */
diff --git a/packages/runtime/src/scr_node_island.c b/packages/runtime/src/scr_node_island.c
index 4c35b86d8..773c42d04 100644
--- a/packages/runtime/src/scr_node_island.c
+++ b/packages/runtime/src/scr_node_island.c
@@ -987,6 +987,9 @@ static void ni_on_node_stack(void (*job)(void *), void *arg) {
       job(arg);
     return;
   }
+  /* Island code is about to run: it sees the current native values of
+   * shared exports (NI-6). */
+  scr_ni_shared_refresh();
   if (ni_stack == NULL) {
     ni_stack = mmap(NULL, NI_STACK, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
     if (ni_stack == MAP_FAILED) ni_oom();
@@ -1131,6 +1134,7 @@ static void ni_host_exit(int code) {
 static void ni_host_run(uint32_t kind, uint32_t token) {
   NI_MARK_BEGIN;
   scr_loop_hosted_run(kind, token);
+  scr_ni_shared_refresh();
   NI_MARK_END;
 }
 
@@ -1174,6 +1178,10 @@ static const ScrNodeBridgeHost ni_host = {
     &scr_ni_host_export_keys,
     &scr_ni_host_export_watch,
     &scr_ni_host_export_release,
+    &scr_ni_host_export_instance_of,
+    &scr_ni_host_shared_table,
+    &scr_ni_host_shared_get,
+    &scr_ni_host_shared_tdz,
 };
 
 typedef struct {
diff --git a/packages/runtime/src/scr_node_island.h b/packages/runtime/src/scr_node_island.h
index 693857c6b..823796491 100644
--- a/packages/runtime/src/scr_node_island.h
+++ b/packages/runtime/src/scr_node_island.h
@@ -140,7 +140,18 @@ int scr_ni_host_export_delete(uint32_t id, const struct ScrNodeValue *key, struc
 int scr_ni_host_export_keys(uint32_t id, struct ScrNodeValue *out);
 void scr_ni_host_export_watch(uint32_t id);
 void scr_ni_host_export_release(uint32_t id);
+/* ── shared modules (scope-B NI-6, scr_node_island_export.c) ── */
+void scr_node_island_share(ScrStr *path, ScrStr *exports, ScrDyn *accessor);
+ScrDyn *scr_node_island_shared_tdz(void);
+ScrDyn *scr_node_island_class_methods_of(ScrDyn *cls, ScrDyn *builder, ScrDyn *ctor);
+void scr_ni_shared_refresh(void);
 void scr_ni_exports_release_all(void); /* at exit, after Node stopped */
+void *scr_ni_value_out_begin(ScrDyn *v, struct ScrNodeValue *out, bool *ok);
+void scr_ni_value_out_end(void *keep);
+int scr_ni_host_export_instance_of(uint32_t id, const struct ScrNodeValue *value);
+void scr_ni_host_shared_table(struct ScrNodeValue *out);
+int scr_ni_host_shared_get(uint32_t mod, uint32_t slot, int mode, struct ScrNodeValue *out);
+void scr_ni_host_shared_tdz(struct ScrNodeValue *out);
 /* Promise settlement callback (SCR_NODE_ISLANDS build of scr_async.c). */
 void scr_promise_on_settle_sync(ScrPromise *in, void (*cb)(ScrPromise *dst, ScrPromise *src));
 
diff --git a/packages/runtime/src/scr_node_island_export.c b/packages/runtime/src/scr_node_island_export.c
index a24cb6428..2aaac7ad6 100644
--- a/packages/runtime/src/scr_node_island_export.c
+++ b/packages/runtime/src/scr_node_island_export.c
@@ -130,6 +130,8 @@ static void ni_ids_del(const void *key) {
 static const void *ni_identity(const ScrDyn *v) {
   switch (v->kind) {
   case SCR_DYN_FUNC:
+    /* A class value is boxed afresh per read: its identity is the class. */
+    if (v->v.fn.class_obj != NULL) return v->v.fn.class_obj;
     return v->v.fn.clo != NULL ? (const void *)v->v.fn.clo : (const void *)v;
   case SCR_DYN_PROMISE:
     return scr_promise_identity_key(v->v.promise);
@@ -143,7 +145,7 @@ static const void *ni_identity(const ScrDyn *v) {
 uint32_t scr_ni_export_flags(const ScrDyn *v) {
   switch (v->kind) {
   case SCR_DYN_FUNC:
-    return SCR_NVF_FUNCTION;
+    return v->v.fn.class_obj != NULL ? SCR_NVF_FUNCTION | SCR_NVF_CONSTRUCTOR : SCR_NVF_FUNCTION;
   case SCR_DYN_PROMISE:
     return SCR_NVF_PROMISE;
   case SCR_DYN_ARR:
@@ -301,6 +303,7 @@ int scr_ni_host_export_call(uint32_t id, const ScrNodeValue *this_, const ScrNod
   scr_dyn_release(self);
   ni_args_free(in, argc, small);
   scr_dyn_release(fn);
+  scr_ni_shared_refresh();
   if (result == NULL || scr_exc_pending()) {
     scr_dyn_release(result);
     return ni_threw(out);
@@ -308,6 +311,8 @@ int scr_ni_host_export_call(uint32_t id, const ScrNodeValue *this_, const ScrNod
   return ni_returned(result, out);
 }
 
+static ScrDyn *ni_class_ctor(const ScrDyn *cls);
+
 int scr_ni_host_export_construct(uint32_t id, const ScrNodeValue *args, size_t argc,
                                  ScrNodeValue *out) {
   ni_keep_set(NULL);
@@ -317,13 +322,25 @@ int scr_ni_host_export_construct(uint32_t id, const ScrNodeValue *args, size_t a
     return ni_threw(out);
   }
   scr_dyn_retain(ctor);
-  ScrDyn *list = scr_dyn_new_arr();
-  for (size_t i = 0; i < argc; i++) scr_dyn_arr_push(list, scr_ni_value_in(&args[i]));
-  ScrStr *what = scr_str_new("constructor", 11);
-  ScrDyn *result = scr_dyn_construct(ctor, list, what);
-  scr_str_release(what);
-  scr_dyn_release(list);
+  ScrDyn *result;
+  ScrDyn *helper = ni_class_ctor(ctor);
+  if (helper != NULL) {
+    /* A native class of a shared module (NI-6): its helper's thunk checks
+     * the arguments against the constructor's parameters. */
+    ScrDyn *small[8];
+    ScrDyn **in = ni_args_in(args, argc, small, 8);
+    result = scr_dyn_call(helper, in, argc, "constructor");
+    ni_args_free(in, argc, small);
+  } else {
+    ScrDyn *list = scr_dyn_new_arr();
+    for (size_t i = 0; i < argc; i++) scr_dyn_arr_push(list, scr_ni_value_in(&args[i]));
+    ScrStr *what = scr_str_new("constructor", 11);
+    result = scr_dyn_construct(ctor, list, what);
+    scr_str_release(what);
+    scr_dyn_release(list);
+  }
   scr_dyn_release(ctor);
+  scr_ni_shared_refresh();
   if (result == NULL || scr_exc_pending()) {
     scr_dyn_release(result);
     return ni_threw(out);
@@ -340,6 +357,7 @@ typedef struct {
   const char *key;
   size_t key_len;
   ScrDyn *table; /* +1 dyn object */
+  ScrDyn *ctor;  /* +1 dyn function constructing an instance (NI-6), or NULL */
 } NiMethods;
 static NiMethods *ni_methods = NULL;
 static size_t ni_nmethods = 0, ni_methods_cap = 0;
@@ -368,11 +386,68 @@ ScrDyn *scr_node_island_class_methods(ScrDyn *value, ScrDyn *builder) {
     ni_methods[ni_nmethods].key = value->v.typed_ref.type_key; /* static */
     ni_methods[ni_nmethods].key_len = value->v.typed_ref.type_key_len;
     ni_methods[ni_nmethods].table = table;
+    ni_methods[ni_nmethods].ctor = NULL;
     ni_nmethods++;
   }
   return scr_dyn_retain(value);
 }
 
+/* NI-6: the method table of a class registered through its class value
+ * (a shared module's exported class), keyed by the same type key its
+ * instances carry. Answers the class value. */
+/* The type key a class value's instances carry: "classval:C" -> "object:C".
+ * Answers whether `key`/`len` is it. */
+static bool ni_instance_key_is(const char *sig, const char *key, size_t len) {
+  if (sig == NULL || key == NULL || strncmp(sig, "classval:", 9) != 0) return false;
+  size_t rest = strlen(sig + 9);
+  return len == 7 + rest && memcmp(key, "object:", 7) == 0 && memcmp(key + 7, sig + 9, rest) == 0;
+}
+
+static NiMethods *ni_methods_of_class(const ScrDyn *cls) {
+  if (cls->kind != SCR_DYN_FUNC || cls->v.fn.class_obj == NULL) return NULL;
+  for (size_t i = 0; i < ni_nmethods; i++)
+    if (ni_instance_key_is(cls->v.fn.sig, ni_methods[i].key, ni_methods[i].key_len))
+      return &ni_methods[i];
+  return NULL;
+}
+
+ScrDyn *scr_node_island_class_methods_of(ScrDyn *cls, ScrDyn *builder, ScrDyn *ctor) {
+  if (cls->kind != SCR_DYN_FUNC || cls->v.fn.class_obj == NULL || cls->v.fn.sig == NULL ||
+      strncmp(cls->v.fn.sig, "classval:", 9) != 0)
+    return scr_dyn_retain(cls);
+  NiMethods *known = ni_methods_of_class(cls);
+  if (known != NULL) {
+    if (known->ctor == NULL && ctor->kind == SCR_DYN_FUNC) known->ctor = scr_dyn_retain(ctor);
+    return scr_dyn_retain(cls);
+  }
+  ScrDyn *table = builder->kind == SCR_DYN_FUNC ? scr_dyn_call(builder, NULL, 0, "class methods")
+                                                : scr_dyn_new_obj();
+  if (table == NULL) return NULL;
+  if (ni_nmethods == ni_methods_cap) {
+    ni_methods_cap = ni_methods_cap ? ni_methods_cap * 2 : 8;
+    NiMethods *grown = realloc(ni_methods, ni_methods_cap * sizeof *grown);
+    if (grown == NULL) ni_export_oom();
+    ni_methods = grown;
+  }
+  size_t rest = strlen(cls->v.fn.sig + 9);
+  char *key = malloc(7 + rest + 1); /* lives as long as the program */
+  if (key == NULL) ni_export_oom();
+  memcpy(key, "object:", 7);
+  memcpy(key + 7, cls->v.fn.sig + 9, rest + 1);
+  ni_methods[ni_nmethods].key = key;
+  ni_methods[ni_nmethods].key_len = 7 + rest;
+  ni_methods[ni_nmethods].table = table;
+  ni_methods[ni_nmethods].ctor = ctor->kind == SCR_DYN_FUNC ? scr_dyn_retain(ctor) : NULL;
+  ni_nmethods++;
+  return scr_dyn_retain(cls);
+}
+
+/* The constructor helper of a native class value (borrowed), or NULL. */
+static ScrDyn *ni_class_ctor(const ScrDyn *cls) {
+  NiMethods *m = ni_methods_of_class(cls);
+  return m != NULL ? m->ctor : NULL;
+}
+
 /* A prototype method of a class capsule (+1), or NULL. An own property the
  * island wrote under the method's name (kept in the capsule's materialized
  * view) hides the method, as an own property hides a prototype's in Node. */
@@ -401,8 +476,11 @@ int scr_ni_host_export_get(uint32_t id, const ScrNodeValue *key, ScrNodeValue *o
   int present = 0;
   if (pk->kind == SCR_DYN_STR) present = scr_dyn_in(target, pk->v.str);
   if (!present && !scr_exc_pending()) {
+    /* A prototype method of a class instance (its table). */
+    ScrDyn *method = ni_class_method(target, pk);
     scr_dyn_release(pk);
     scr_dyn_release(k);
+    if (method != NULL) return ni_returned(method, out);
     return 2;
   }
   ScrDyn *result = scr_exc_pending() ? NULL : scr_dyn_reflect_get(target, pk, target);
@@ -432,6 +510,7 @@ int scr_ni_host_export_set(uint32_t id, const ScrNodeValue *key, const ScrNodeVa
   bool ok = scr_dyn_reflect_set(target, k, v, target);
   scr_dyn_release(v);
   scr_dyn_release(k);
+  scr_ni_shared_refresh();
   if (scr_exc_pending()) return ni_threw(out);
   (void)ok; /* a refused write is silent outside strict mode; Node's setter
              * interceptor reports the same */
@@ -447,6 +526,11 @@ int scr_ni_host_export_has(uint32_t id, const ScrNodeValue *key) {
   int present = 0;
   if (pk != NULL && pk->kind == SCR_DYN_STR) present = scr_dyn_in(target, pk->v.str);
   if (scr_exc_pending()) scr_exc_clear();
+  if (!present && pk != NULL) {
+    ScrDyn *method = ni_class_method(target, pk);
+    present = method != NULL;
+    scr_dyn_release(method);
+  }
   scr_dyn_release(pk);
   scr_dyn_release(k);
   return present;
@@ -481,7 +565,9 @@ int scr_ni_host_export_keys(uint32_t id, ScrNodeValue *out) {
   if (json == NULL || json->kind != SCR_DYN_STR) {
     scr_dyn_release(json);
     if (scr_exc_pending()) return ni_threw(out);
-    json = scr_dyn_new_str(scr_str_new("[]", 2));
+    ScrStr *empty = scr_str_new("[]", 2);
+    json = scr_dyn_new_str(empty);
+    scr_str_release(empty);
   }
   memset(out, 0, sizeof *out);
   out->tag = SCR_NV_JSON;
@@ -509,6 +595,19 @@ void scr_ni_host_export_release(uint32_t id) {
   scr_dyn_release(v);
 }
 
+/* `value instanceof C` for the representative of native class C: the
+ * value is an instance of C's own type key (NI-6 shortcut: instances of
+ * native subclasses of C answer false; NOTES.md). */
+int scr_ni_host_export_instance_of(uint32_t id, const ScrNodeValue *value) {
+  ScrDyn *ctor = scr_ni_export_value(id);
+  if (ctor == NULL || ctor->kind != SCR_DYN_FUNC || ctor->v.fn.class_obj == NULL) return 0;
+  ScrDyn *v = scr_ni_value_in(value);
+  int is = v->kind == SCR_DYN_TYPED_REF &&
+           ni_instance_key_is(ctor->v.fn.sig, v->v.typed_ref.type_key, v->v.typed_ref.type_key_len);
+  scr_dyn_release(v);
+  return is;
+}
+
 /* ── promises into Node ───────────────────────────────────────────────── */
 
 typedef struct {
@@ -579,8 +678,252 @@ void scr_ni_host_export_watch(uint32_t id) {
   scr_promise_on_settle_sync(p, ni_promise_settled);
 }
 
-/* At exit, once Node stopped: everything the export table and the class
- * tables hold (the RC audit counts them). */
+/* ── shared modules (scope-B NI-6) ────────────────────────────────────
+ * A module the program compiled and island code also imports exists once:
+ * the program registers it (nodeIsland.share) with its accessor, a
+ * compiler-generated function answering the current values of its exports
+ * as a dyn array (the TDZ sentinel for a binding whose declaration has not
+ * run). The bootstrap's loader hooks (scr_node_island_hooks.cjs) resolve
+ * island imports of the module to a generated ES module whose bindings
+ * read those values; the bindings that can change (exported lets, and
+ * bindings still in their temporal dead zone when the generated module
+ * linked) are kept current by pushes: at each entry into Node and before
+ * each return from a native callback, the runtime compares the bound
+ * values with the last pushed ones and pushes the changes. Island code only
+ * runs inside those entries, so it never observes a stale binding. */
+
+typedef struct {
+  ScrStr *path;     /* +1 */
+  ScrStr *exports;  /* +1 JSON [{"name","kind"}] */
+  ScrDyn *accessor; /* +1 */
+  uint32_t nslots;
+  ScrDyn **last;    /* +1 each, NULL when unbound */
+  uint8_t *bound;   /* 0 unbound, 1 bound, 2 bound late (not yet pushed) */
+  uint32_t nbound;
+} NiShared;
+
+static NiShared *ni_shared = NULL;
+static uint32_t ni_nshared = 0, ni_shared_cap = 0;
+static uint32_t ni_shared_bound = 0; /* bound slots over all modules */
+static bool ni_refreshing = false;
+static ScrDyn *ni_tdz = NULL;
+
+static ScrDyn *ni_tdz_value(void) {
+  if (ni_tdz == NULL) ni_tdz = scr_dyn_new_obj();
+  return ni_tdz;
+}
+
+/* nodeIsland.sharedTdz: the sentinel an accessor answers for a binding in
+ * its temporal dead zone (+1). */
+ScrDyn *scr_node_island_shared_tdz(void) { return scr_dyn_retain(ni_tdz_value()); }
+
+/* nodeIsland.share(path, exports JSON, accessor): registers a shared
+ * module before any island code runs. Never loads Node. */
+void scr_node_island_share(ScrStr *path, ScrStr *exports, ScrDyn *accessor) {
+  for (uint32_t i = 0; i < ni_nshared; i++)
+    if (ni_shared[i].path->len == path->len &&
+        memcmp(ni_shared[i].path->data, path->data, path->len) == 0)
+      return;
+  /* Released at exit (after Node stopped, when it started: atexit order). */
+  if (ni_nshared == 0 && ni_shared_cap == 0) scr_atexit(scr_ni_exports_release_all);
+  if (ni_nshared == ni_shared_cap) {
+    ni_shared_cap = ni_shared_cap ? ni_shared_cap * 2 : 8;
+    NiShared *grown = realloc(ni_shared, ni_shared_cap * sizeof *grown);
+    if (grown == NULL) ni_export_oom();
+    ni_shared = grown;
+  }
+  NiShared *m = &ni_shared[ni_nshared++];
+  memset(m, 0, sizeof *m);
+  m->path = scr_str_retain(path);
+  m->exports = scr_str_retain(exports);
+  m->accessor = scr_dyn_retain(accessor);
+  /* The slot count: the accessor's array length is the export count. */
+  uint32_t n = 0;
+  for (size_t i = 0; i < exports->len; i++) n += exports->data[i] == '{';
+  m->nslots = n;
+  m->last = calloc(n > 0 ? n : 1, sizeof *m->last);
+  m->bound = calloc(n > 0 ? n : 1, 1);
+  if (m->last == NULL || m->bound == NULL) ni_export_oom();
+}
+
+/* The current export values of module `m` (+1 dyn array), or NULL. */
+static ScrDyn *ni_shared_values(NiShared *m) {
+  ScrDyn *values = scr_dyn_call(m->accessor, NULL, 0, "shared module");
+  if (values == NULL) scr_exc_clear();
+  return values;
+}
+
+void scr_ni_host_shared_table(ScrNodeValue *out) {
+  ni_keep_set(NULL);
+  /* Each module's file as Node resolves it: in the shipped module tree. */
+  char **paths = calloc(ni_nshared > 0 ? ni_nshared : 1, sizeof *paths);
+  if (paths == NULL) ni_export_oom();
+  size_t len = 2;
+  for (uint32_t i = 0; i < ni_nshared; i++) {
+    paths[i] = scr_ni_module_path(ni_shared[i].path);
+    len += strlen(paths[i]) * 2 + ni_shared[i].exports->len + 32;
+  }
+  char *buf = malloc(len);
+  if (buf == NULL) ni_export_oom();
+  size_t at = 0;
+  buf[at++] = '[';
+  for (uint32_t i = 0; i < ni_nshared; i++) {
+    NiShared *m = &ni_shared[i];
+    if (i > 0) buf[at++] = ',';
+    at += (size_t)sprintf(buf + at, "{\"path\":\"");
+    for (const char *p = paths[i]; *p != '\0'; p++) {
+      char c = *p;
+      if (c == '"' || c == '\\') buf[at++] = '\\';
+      buf[at++] = c;
+    }
+    free(paths[i]);
+    at += (size_t)sprintf(buf + at, "\",\"exports\":");
+    memcpy(buf + at, m->exports->data, m->exports->len);
+    at += m->exports->len;
+    buf[at++] = '}';
+  }
+  buf[at++] = ']';
+  free(paths);
+  ScrStr *text = scr_str_new(buf, at);
+  ScrDyn *json = scr_dyn_new_str(text);
+  scr_str_release(text);
+  free(buf);
+  memset(out, 0, sizeof *out);
+  out->tag = SCR_NV_STRING;
+  out->u.str.data = json->v.str->data;
+  out->u.str.len = json->v.str->len;
+  ni_keep_set(json);
+}
+
+static void ni_shared_bind(NiShared *m, uint32_t slot, ScrDyn *value, uint8_t how) {
+  if (m->bound[slot] == 0) {
+    m->nbound++;
+    ni_shared_bound++;
+  }
+  m->bound[slot] = how;
+  scr_dyn_release(m->last[slot]);
+  m->last[slot] = value != NULL ? scr_dyn_retain(value) : NULL;
+}
+
+int scr_ni_host_shared_get(uint32_t mod, uint32_t slot, int mode, ScrNodeValue *out) {
+  ni_keep_set(NULL);
+  memset(out, 0, sizeof *out);
+  if (mod >= ni_nshared || slot >= ni_shared[mod].nslots) return 3;
+  NiShared *m = &ni_shared[mod];
+  ScrDyn *values = ni_shared_values(m);
+  if (values == NULL) return 3;
+  ScrDyn *v = scr_dyn_arr_at(values, slot);
+  scr_dyn_release(values);
+  if (v == ni_tdz) {
+    scr_dyn_release(v);
+    if (mode == 2) ni_shared_bind(m, slot, NULL, 2);
+    return 3;
+  }
+  /* Arrays still cross as copies (NI-5): a copy of shared state would
+   * diverge silently, so the island read throws instead. */
+  if (v->kind == SCR_DYN_ARR ||
+      (v->kind == SCR_DYN_TYPED_REF && scr_dyn_typed_ref_array_ops(v) != NULL)) {
+    scr_dyn_release(v);
+    static const char message[] =
+        "scriptc: an array exported by a shared module cannot cross into a Node island yet";
+    scr_throw_error_msg(SCR_ERR_TYPE, message, sizeof message - 1);
+    return ni_threw(out);
+  }
+  if (mode == 1 || mode == 2) ni_shared_bind(m, slot, v, 1);
+  return ni_returned(v, out);
+}
+
+void scr_ni_host_shared_tdz(ScrNodeValue *out) {
+  ni_keep_set(NULL);
+  size_t cap = 64, at = 0;
+  char *buf = malloc(cap);
+  if (buf == NULL) ni_export_oom();
+  buf[at++] = '[';
+  for (uint32_t i = 0; i < ni_nshared; i++) {
+    NiShared *m = &ni_shared[i];
+    ScrDyn *values = ni_shared_values(m);
+    if (values == NULL) continue;
+    for (uint32_t j = 0; j < m->nslots; j++) {
+      ScrDyn *v = scr_dyn_arr_at(values, j);
+      if (v == ni_tdz) {
+        if (at + 32 > cap) {
+          cap *= 2;
+          char *grown = realloc(buf, cap);
+          if (grown == NULL) ni_export_oom();
+          buf = grown;
+        }
+        at += (size_t)sprintf(buf + at, "%s[%u,%u]", at > 1 ? "," : "", i, j);
+      }
+      scr_dyn_release(v);
+    }
+    scr_dyn_release(values);
+  }
+  buf[at++] = ']';
+  ScrStr *text = scr_str_new(buf, at);
+  ScrDyn *json = scr_dyn_new_str(text);
+  scr_str_release(text);
+  free(buf);
+  memset(out, 0, sizeof *out);
+  out->tag = SCR_NV_STRING;
+  out->u.str.data = json->v.str->data;
+  out->u.str.len = json->v.str->len;
+  ni_keep_set(json);
+}
+
+typedef struct {
+  uint32_t mod, slot;
+  const ScrNodeValue *value;
+} NiPush;
+
+static void ni_push_job(void *p) {
+  NiPush *a = p;
+  scr_ni_bridge_loaded()->shared_push(a->mod, a->slot, a->value);
+}
+
+/* Pushes the bound exports whose native values changed since the last
+ * push. Cheap when nothing is bound. */
+void scr_ni_shared_refresh(void) {
+  if (ni_shared_bound == 0 || ni_refreshing || scr_ni_bridge_loaded() == NULL) return;
+  ni_refreshing = true;
+  bool pending = scr_exc_pending();
+  ScrCaught *saved = pending ? scr_exc_take() : NULL;
+  for (uint32_t i = 0; i < ni_nshared; i++) {
+    NiShared *m = &ni_shared[i];
+    if (m->nbound == 0) continue;
+    ScrDyn *values = ni_shared_values(m);
+    if (values == NULL) continue;
+    for (uint32_t j = 0; j < m->nslots; j++) {
+      if (m->bound[j] == 0) continue;
+      ScrDyn *v = scr_dyn_arr_at(values, j);
+      if (v == ni_tdz || (m->bound[j] == 1 && m->last[j] != NULL && scr_dyn_strict_eq(v, m->last[j]))) {
+        scr_dyn_release(v);
+        continue;
+      }
+      ScrNodeValue nv;
+      bool ok = false;
+      void *keep = scr_ni_value_out_begin(v, &nv, &ok);
+      if (ok) {
+        NiPush a = {i, j, &nv};
+        scr_ni_on_node_stack(ni_push_job, &a);
+      } else {
+        scr_exc_clear();
+      }
+      scr_ni_value_out_end(keep);
+      scr_dyn_release(m->last[j]);
+      m->last[j] = v;
+      m->bound[j] = 1;
+    }
+    scr_dyn_release(values);
+  }
+  if (saved != NULL) {
+    scr_rethrow(saved);
+    scr_caught_release(saved);
+  }
+  ni_refreshing = false;
+}
+
+/* At exit, once Node stopped: everything the export table, the class
+ * tables and the shared modules hold (the RC audit counts them). */
 void scr_ni_exports_release_all(void) {
   ni_keep_set(NULL);
   for (uint32_t i = 1; i < ni_exports_len; i++) {
@@ -595,8 +938,24 @@ void scr_ni_exports_release_all(void) {
   free(ni_ids);
   ni_ids = NULL;
   ni_ids_cap = ni_ids_len = ni_ids_dead = 0;
-  for (size_t i = 0; i < ni_nmethods; i++) scr_dyn_release(ni_methods[i].table);
+  for (size_t i = 0; i < ni_nmethods; i++) {
+    scr_dyn_release(ni_methods[i].table);
+    scr_dyn_release(ni_methods[i].ctor);
+  }
   ni_nmethods = 0;
+  for (uint32_t i = 0; i < ni_nshared; i++) {
+    NiShared *m = &ni_shared[i];
+    for (uint32_t j = 0; j < m->nslots; j++) scr_dyn_release(m->last[j]);
+    free(m->last);
+    free(m->bound);
+    scr_str_release(m->path);
+    scr_str_release(m->exports);
+    scr_dyn_release(m->accessor);
+  }
+  ni_nshared = 0;
+  ni_shared_bound = 0;
+  scr_dyn_release(ni_tdz);
+  ni_tdz = NULL;
 }
 
 #endif
diff --git a/packages/runtime/src/scr_node_island_handle.c b/packages/runtime/src/scr_node_island_handle.c
index b9f8c7178..78b016355 100644
--- a/packages/runtime/src/scr_node_island_handle.c
+++ b/packages/runtime/src/scr_node_island_handle.c
@@ -572,7 +572,10 @@ static bool nh_export_value(ScrDyn *v, ScrNodeValue *out, NhKeep *keep) {
     scr_ni_export_out(v, out);
     return true;
   }
-  if (v->kind == SCR_DYN_OBJ || v->kind == SCR_DYN_ARR) {
+  /* Arrays (dyn, and typed array capsules: NI-6 shortcut, as for dyn
+   * arrays) keep NI-4's JSON copy. */
+  if (v->kind == SCR_DYN_OBJ || v->kind == SCR_DYN_ARR ||
+      (v->kind == SCR_DYN_TYPED_REF && scr_dyn_typed_ref_array_ops(v) != NULL)) {
     ScrStr *gap = scr_str_new("", 0);
     ScrDyn *json = scr_json_stringify_replacer(v, scr_dyn_undefined(), gap);
     scr_str_release(gap);
@@ -752,6 +755,7 @@ static void nh_call_job(void *p) {
 }
 
 static int nh_run(NhCall *c) {
+  scr_ni_shared_refresh();
   scr_ni_on_node_stack(nh_call_job, c);
   return c->threw;
 }
@@ -1133,6 +1137,20 @@ bool scr_ni_value_out(ScrDyn *v, ScrNodeValue *out) {
   return nh_to_node(v, out, &nh_out_keep);
 }
 
+/* NI-6: a conversion whose keep belongs to the caller, for values the
+ * runtime pushes into Node between other conversions (shared modules). */
+void *scr_ni_value_out_begin(ScrDyn *v, ScrNodeValue *out, bool *ok) {
+  NhKeep *k = calloc(1, sizeof *k);
+  if (k == NULL) nh_oom();
+  *ok = nh_to_node(v, out, k);
+  return k;
+}
+
+void scr_ni_value_out_end(void *keep) {
+  nh_keep_done(keep);
+  free(keep);
+}
+
 ScrDyn *scr_ni_value_in(const ScrNodeValue *v) {
   ScrDyn *d = nh_from_node(v);
   return d != NULL ? d : scr_dyn_retain(scr_dyn_undefined());
@@ -1216,6 +1234,21 @@ static bool nh_op_set(void *h, const char *key, size_t key_len, const ScrDyn *va
   return true; /* handled; a throw stays pending */
 }
 
+/* A member that reads back as one of the program's own functions (a
+ * module the program shares with its islands gives them its native
+ * exports): called natively, with the island object as the receiver. */
+static bool nh_is_native_function(const ScrDyn *fn) {
+  return !scr_ni_is_handle(fn) && scr_dyn_is_callable(fn);
+}
+
+static ScrDyn *nh_call_native(ScrDyn *fn, ScrDyn *this_, ScrDyn *const *args, size_t argc,
+                              const char *what) {
+  scr_dyn_this_push_dyn(this_);
+  ScrDyn *result = scr_dyn_call(fn, args, argc, what);
+  scr_dyn_this_pop();
+  return result;
+}
+
 /* obj.m(...) from dynamic code: the member read, then the call with obj
  * as the receiver; a member that is not a function throws Node's TypeError
  * with the call site's text (`what`), as V8 words it. */
@@ -1224,6 +1257,11 @@ static ScrDyn *nh_op_invoke(void *h, ScrDyn *self, const char *method, ScrDyn *c
   (void)h;
   ScrDyn *fn = scr_ni_get_str(self, method, strlen(method));
   if (fn == NULL) return NULL;
+  if (nh_is_native_function(fn)) {
+    ScrDyn *result = nh_call_native(fn, self, args, argc, what != NULL ? what : method);
+    scr_dyn_release(fn);
+    return result;
+  }
   if (!scr_ni_is_function(fn)) {
     scr_dyn_release(fn);
     char message[512];
@@ -1327,6 +1365,7 @@ ScrDyn *scr_node_island_apply(ScrDyn *fn, ScrDyn *args) {
 ScrDyn *scr_node_island_apply_to(ScrDyn *fn, ScrDyn *this_, ScrDyn *args) {
   ScrDyn *const *items;
   size_t argc = ni_libcall_args(args, &items);
+  if (nh_is_native_function(fn)) return nh_call_native(fn, this_, items, argc, "value");
   return scr_ni_call(fn, this_, items, argc);
 }
 
diff --git a/packages/runtime/src/scr_node_island_hooks.cjs b/packages/runtime/src/scr_node_island_hooks.cjs
new file mode 100644
index 000000000..b587132cf
--- /dev/null
+++ b/packages/runtime/src/scr_node_island_hooks.cjs
@@ -0,0 +1,149 @@
+// ── shared modules (scope-B NI-6) ──────────────────────────────────────
+// The design's hooks.mjs. scripts/node-island-host.mjs appends this file to
+// scr_node_island_host.cjs, so it runs in the bootstrap's scope (CommonJS:
+// the bootstrap is Node's main script).
+//
+// A module the program compiled that island code imports must exist once.
+// Synchronous, in-thread loader hooks (module.registerHooks) resolve every
+// island import or require() of such a module to a generated ES module
+// (served at the module's own file URL) whose bindings hold the live native exports: the
+// natives sharedGet/sharedTable/sharedTdz ask the runtime directly. An
+// export that can change (an exported let, var or function declaration,
+// whose binding JavaScript allows reassigning, or a binding still in its
+// temporal dead zone when the module linked) is bound: the runtime pushes
+// each new native value (sharedPush) before island code can observe it.
+//
+// Temporal dead zone across a cycle: when an island module loads while a
+// shared module's bindings are not yet initialized (the native module is
+// still evaluating, as in `core` -> island `ext` -> `core`), the load goes
+// through an entry module that imports the island module and declares
+// those bindings after the import. The generated module re-exports them
+// from the entry, so while the island module evaluates they are in their
+// temporal dead zone exactly as in Node (V8 throws its own ReferenceError
+// with the importer's binding name), and they are pushed once the native
+// declarations ran.
+// oxlint-disable-next-line no-unused-vars -- called by scr_node_island_host.cjs, which this file is appended to
+function scriptcSharedModules(nativeHost) {
+  const { registerHooks } = require("node:module");
+  const { fileURLToPath, pathToFileURL } = require("node:url");
+  const { dirname, join } = require("node:path");
+  const table = JSON.parse(nativeHost.sharedTable());
+  const none = { entry: (path, load) => load(null), push() {} };
+  if (table.length === 0) return none;
+  const byUrl = new Map();
+  table.forEach((m, id) => byUrl.set(pathToFileURL(m.path).href, id));
+  const TDZ = Symbol("scriptc.tdz");
+  const setters = new Map(); // `${mod}:${slot}` -> [(value) => void]
+  const entries = new Map(); // entry URL -> { target, late: [[mod, slot]] }
+  let entrySeq = 0;
+  let current = null; // the entry being loaded
+
+  function addSetter(mod, slot, set) {
+    const key = `${mod}:${slot}`;
+    const list = setters.get(key);
+    if (list === undefined) setters.set(key, [set]);
+    else list.push(set);
+  }
+
+  const shared = {
+    get(mod, slot) {
+      return nativeHost.sharedGet(mod, slot, 0, TDZ);
+    },
+    bind(mod, slot, set) {
+      addSetter(mod, slot, set);
+      return nativeHost.sharedGet(mod, slot, 1, TDZ);
+    },
+    late(mod, slot, set) {
+      addSetter(mod, slot, set);
+      const v = nativeHost.sharedGet(mod, slot, 2, TDZ);
+      return v === TDZ ? undefined : v;
+    },
+  };
+  Object.defineProperty(globalThis, Symbol.for("scriptc.shared"), { value: shared });
+
+  const lateName = (mod, slot) => `__scriptc_${mod}_${slot}`;
+
+  function sharedSource(mod) {
+    const m = table[mod];
+    const lines = ['const __s = globalThis[Symbol.for("scriptc.shared")];'];
+    const lateIn = current === null ? null : entries.get(current);
+    m.exports.forEach((e, slot) => {
+      const name = JSON.stringify(e.name);
+      const local = `__e${slot}`;
+      const tdz = nativeHost.sharedGet(mod, slot, 0, TDZ) === TDZ;
+      if (tdz && lateIn !== null && lateIn.late.some(([a, b]) => a === mod && b === slot)) {
+        lines.push(`export { ${lateName(mod, slot)} as ${name} } from ${JSON.stringify(current)};`);
+      } else if (tdz) {
+        // Reached outside an island load (a lazy require): no entry can hold
+        // the dead zone; the binding reads undefined until its declaration
+        // runs (NOTES.md shortcut).
+        lines.push(`let ${local} = __s.late(${mod}, ${slot}, (v) => { ${local} = v; });`);
+        lines.push(`export { ${local} as ${name} };`);
+      } else if (e.kind === "let" || e.kind === "var" || e.kind === "function") {
+        // A function declaration's binding is reassignable, like `var`:
+        // the island must see the current function, not the first one.
+        lines.push(`let ${local} = __s.bind(${mod}, ${slot}, (v) => { ${local} = v; });`);
+        lines.push(`export { ${local} as ${name} };`);
+      } else {
+        lines.push(`const ${local} = __s.get(${mod}, ${slot});`);
+        lines.push(`export { ${local} as ${name} };`);
+      }
+    });
+    return lines.join("\n");
+  }
+
+  function entrySource(url) {
+    const e = entries.get(url);
+    const lines = [`import ${JSON.stringify(e.target)};`];
+    lines.push('const __s = globalThis[Symbol.for("scriptc.shared")];');
+    for (const [mod, slot] of e.late) {
+      const n = lateName(mod, slot);
+      lines.push(`export let ${n} = __s.late(${mod}, ${slot}, (v) => { ${n} = v; });`);
+    }
+    return lines.join("\n");
+  }
+
+  registerHooks({
+    resolve(specifier, context, nextResolve) {
+      const asUrl = specifier.startsWith("/") ? pathToFileURL(specifier).href : specifier;
+      if (entries.has(asUrl)) return { url: asUrl, shortCircuit: true };
+      const resolved = nextResolve(specifier, context);
+      // A shared module keeps its own file URL (require() and import key
+      // their module records alike only for file URLs); load answers it.
+      if (resolved.url.startsWith("file:") && byUrl.has(resolved.url))
+        return { url: resolved.url, format: "module", shortCircuit: true };
+      return resolved;
+    },
+    load(url, context, nextLoad) {
+      const mod = byUrl.get(url);
+      if (mod !== undefined)
+        return { format: "module", source: sharedSource(mod), shortCircuit: true };
+      if (entries.has(url))
+        return { format: "module", source: entrySource(url), shortCircuit: true };
+      return nextLoad(url, context);
+    },
+  });
+
+  return {
+    /** The entry to load the island module at `path` through, or null when
+     * no shared binding is in its temporal dead zone. Run `load` with it. */
+    entry(path, load) {
+      const late = JSON.parse(nativeHost.sharedTdz());
+      if (late.length === 0) return load(null);
+      // A file URL beside the island module (never on disk: the load hook
+      // answers it), so require() and import key it alike.
+      const url = pathToFileURL(join(dirname(path), `__scriptc_entry_${++entrySeq}.mjs`)).href;
+      entries.set(url, { target: pathToFileURL(path).href, late });
+      const outer = current;
+      current = url;
+      try {
+        return load(fileURLToPath(url));
+      } finally {
+        current = outer;
+      }
+    },
+    push(mod, slot, value) {
+      for (const set of setters.get(`${mod}:${slot}`) ?? []) set(value);
+    },
+  };
+}
diff --git a/packages/runtime/src/scr_node_island_host.cjs b/packages/runtime/src/scr_node_island_host.cjs
index b9f148e75..e114f7235 100644
--- a/packages/runtime/src/scr_node_island_host.cjs
+++ b/packages/runtime/src/scr_node_island_host.cjs
@@ -222,11 +222,24 @@ function call(id, sync, file, specifier, name, argsJson) {
 // answers a promise of the namespace.
 const { pathToFileURL } = require("node:url");
 
+// Island imports of modules the program shares resolve to their native
+// exports (NI-6, scr_node_island_hooks.cjs, appended to this file).
+let sharedModules = null;
+
 function load(path, esm) {
   // A built-in module's name, with or without the node: prefix.
   if (isBuiltin(path)) return require(path);
+  if (sharedModules === null) sharedModules = scriptcSharedModules(nativeHost);
   if (esm) return import(pathToFileURL(path).href);
-  return createRequire(path)(path);
+  const load = createRequire(path);
+  return sharedModules.entry(path, (entry) => {
+    if (entry !== null) load(entry);
+    return load(path);
+  });
+}
+
+function sharedPush(mod, slot, value) {
+  if (sharedModules !== null) sharedModules.push(mod, slot, value);
 }
 
 // ── the hosted loop (scope-B NI-3) ─────────────────────────────────────
@@ -495,4 +508,5 @@ globalThis.__scriptcNodeIsland = {
   nextTick,
   emit,
   load,
+  sharedPush,
 };
diff --git a/packages/runtime/src/scr_node_island_host.h b/packages/runtime/src/scr_node_island_host.h
index bdcd41892..23209bcda 100644
--- a/packages/runtime/src/scr_node_island_host.h
+++ b/packages/runtime/src/scr_node_island_host.h
@@ -1,4 +1,5 @@
-/* Generated by scripts/node-island-host.mjs from scr_node_island_host.cjs.
+/* Generated by scripts/node-island-host.mjs from scr_node_island_host.cjs
+ * and scr_node_island_hooks.cjs.
  * Do not edit: change the .cjs file and rerun the script. */
 #ifndef SCR_NODE_ISLAND_HOST_H
 #define SCR_NODE_ISLAND_HOST_H
@@ -228,11 +229,24 @@ static const char scr_node_island_host_js[] =
     "// answers a promise of the namespace.\012"
     "const { pathToFileURL } = require(\"node:url\");\012"
     "\012"
+    "// Island imports of modules the program shares resolve to their native\012"
+    "// exports (NI-6, scr_node_island_hooks.cjs, appended to this file).\012"
+    "let sharedModules = null;\012"
+    "\012"
     "function load(path, esm) {\012"
     "  // A built-in module's name, with or without the node: prefix.\012"
     "  if (isBuiltin(path)) return require(path);\012"
+    "  if (sharedModules === null) sharedModules = scriptcSharedModules(nativeHost);\012"
     "  if (esm) return import(pathToFileURL(path).href);\012"
-    "  return createRequire(path)(path);\012"
+    "  const load = createRequire(path);\012"
+    "  return sharedModules.entry(path, (entry) => {\012"
+    "    if (entry !== null) load(entry);\012"
+    "    return load(path);\012"
+    "  });\012"
+    "}\012"
+    "\012"
+    "function sharedPush(mod, slot, value) {\012"
+    "  if (sharedModules !== null) sharedModules.push(mod, slot, value);\012"
     "}\012"
     "\012"
     "// \342\224\200\342\224\200 the hosted loop (scope-B NI-3) \342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\012"
@@ -501,6 +515,157 @@ static const char scr_node_island_host_js[] =
     "  nextTick,\012"
     "  emit,\012"
     "  load,\012"
-    "};\012";
+    "  sharedPush,\012"
+    "};\012"
+    "\012"
+    "// \342\224\200\342\224\200 shared modules (scope-B NI-6) \342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\342\224\200\012"
+    "// The design's hooks.mjs. scripts/node-island-host.mjs appends this file to\012"
+    "// scr_node_island_host.cjs, so it runs in the bootstrap's scope (CommonJS:\012"
+    "// the bootstrap is Node's main script).\012"
+    "//\012"
+    "// A module the program compiled that island code imports must exist once.\012"
+    "// Synchronous, in-thread loader hooks (module.registerHooks) resolve every\012"
+    "// island import or require() of such a module to a generated ES module\012"
+    "// (served at the module's own file URL) whose bindings hold the live native exports: the\012"
+    "// natives sharedGet/sharedTable/sharedTdz ask the runtime directly. An\012"
+    "// export that can change (an exported let, var or function declaration,\012"
+    "// whose binding JavaScript allows reassigning, or a binding still in its\012"
+    "// temporal dead zone when the module linked) is bound: the runtime pushes\012"
+    "// each new native value (sharedPush) before island code can observe it.\012"
+    "//\012"
+    "// Temporal dead zone across a cycle: when an island module loads while a\012"
+    "// shared module's bindings are not yet initialized (the native module is\012"
+    "// still evaluating, as in `core` -> island `ext` -> `core`), the load goes\012"
+    "// through an entry module that imports the island module and declares\012"
+    "// those bindings after the import. The generated module re-exports them\012"
+    "// from the entry, so while the island module evaluates they are in their\012"
+    "// temporal dead zone exactly as in Node (V8 throws its own ReferenceError\012"
+    "// with the importer's binding name), and they are pushed once the native\012"
+    "// declarations ran.\012"
+    "// oxlint-disable-next-line no-unused-vars -- called by scr_node_island_host.cjs, which this file is appended to\012"
+    "function scriptcSharedModules(nativeHost) {\012"
+    "  const { registerHooks } = require(\"node:module\");\012"
+    "  const { fileURLToPath, pathToFileURL } = require(\"node:url\");\012"
+    "  const { dirname, join } = require(\"node:path\");\012"
+    "  const table = JSON.parse(nativeHost.sharedTable());\012"
+    "  const none = { entry: (path, load) => load(null), push() {} };\012"
+    "  if (table.length === 0) return none;\012"
+    "  const byUrl = new Map();\012"
+    "  table.forEach((m, id) => byUrl.set(pathToFileURL(m.path).href, id));\012"
+    "  const TDZ = Symbol(\"scriptc.tdz\");\012"
+    "  const setters = new Map(); // `${mod}:${slot}` -> [(value) => void]\012"
+    "  const entries = new Map(); // entry URL -> { target, late: [[mod, slot]] }\012"
+    "  let entrySeq = 0;\012"
+    "  let current = null; // the entry being loaded\012"
+    "\012"
+    "  function addSetter(mod, slot, set) {\012"
+    "    const key = `${mod}:${slot}`;\012"
+    "    const list = setters.get(key);\012"
+    "    if (list === undefined) setters.set(key, [set]);\012"
+    "    else list.push(set);\012"
+    "  }\012"
+    "\012"
+    "  const shared = {\012"
+    "    get(mod, slot) {\012"
+    "      return nativeHost.sharedGet(mod, slot, 0, TDZ);\012"
+    "    },\012"
+    "    bind(mod, slot, set) {\012"
+    "      addSetter(mod, slot, set);\012"
+    "      return nativeHost.sharedGet(mod, slot, 1, TDZ);\012"
+    "    },\012"
+    "    late(mod, slot, set) {\012"
+    "      addSetter(mod, slot, set);\012"
+    "      const v = nativeHost.sharedGet(mod, slot, 2, TDZ);\012"
+    "      return v === TDZ \077 undefined : v;\012"
+    "    },\012"
+    "  };\012"
+    "  Object.defineProperty(globalThis, Symbol.for(\"scriptc.shared\"), { value: shared });\012"
+    "\012"
+    "  const lateName = (mod, slot) => `__scriptc_${mod}_${slot}`;\012"
+    "\012"
+    "  function sharedSource(mod) {\012"
+    "    const m = table[mod];\012"
+    "    const lines = ['const __s = globalThis[Symbol.for(\"scriptc.shared\")];'];\012"
+    "    const lateIn = current === null \077 null : entries.get(current);\012"
+    "    m.exports.forEach((e, slot) => {\012"
+    "      const name = JSON.stringify(e.name);\012"
+    "      const local = `__e${slot}`;\012"
+    "      const tdz = nativeHost.sharedGet(mod, slot, 0, TDZ) === TDZ;\012"
+    "      if (tdz && lateIn !== null && lateIn.late.some(([a, b]) => a === mod && b === slot)) {\012"
+    "        lines.push(`export { ${lateName(mod, slot)} as ${name} } from ${JSON.stringify(current)};`);\012"
+    "      } else if (tdz) {\012"
+    "        // Reached outside an island load (a lazy require): no entry can hold\012"
+    "        // the dead zone; the binding reads undefined until its declaration\012"
+    "        // runs (NOTES.md shortcut).\012"
+    "        lines.push(`let ${local} = __s.late(${mod}, ${slot}, (v) => { ${local} = v; });`);\012"
+    "        lines.push(`export { ${local} as ${name} };`);\012"
+    "      } else if (e.kind === \"let\" || e.kind === \"var\" || e.kind === \"function\") {\012"
+    "        // A function declaration's binding is reassignable, like `var`:\012"
+    "        // the island must see the current function, not the first one.\012"
+    "        lines.push(`let ${local} = __s.bind(${mod}, ${slot}, (v) => { ${local} = v; });`);\012"
+    "        lines.push(`export { ${local} as ${name} };`);\012"
+    "      } else {\012"
+    "        lines.push(`const ${local} = __s.get(${mod}, ${slot});`);\012"
+    "        lines.push(`export { ${local} as ${name} };`);\012"
+    "      }\012"
+    "    });\012"
+    "    return lines.join(\"\\n\");\012"
+    "  }\012"
+    "\012"
+    "  function entrySource(url) {\012"
+    "    const e = entries.get(url);\012"
+    "    const lines = [`import ${JSON.stringify(e.target)};`];\012"
+    "    lines.push('const __s = globalThis[Symbol.for(\"scriptc.shared\")];');\012"
+    "    for (const [mod, slot] of e.late) {\012"
+    "      const n = lateName(mod, slot);\012"
+    "      lines.push(`export let ${n} = __s.late(${mod}, ${slot}, (v) => { ${n} = v; });`);\012"
+    "    }\012"
+    "    return lines.join(\"\\n\");\012"
+    "  }\012"
+    "\012"
+    "  registerHooks({\012"
+    "    resolve(specifier, context, nextResolve) {\012"
+    "      const asUrl = specifier.startsWith(\"/\") \077 pathToFileURL(specifier).href : specifier;\012"
+    "      if (entries.has(asUrl)) return { url: asUrl, shortCircuit: true };\012"
+    "      const resolved = nextResolve(specifier, context);\012"
+    "      // A shared module keeps its own file URL (require() and import key\012"
+    "      // their module records alike only for file URLs); load answers it.\012"
+    "      if (resolved.url.startsWith(\"file:\") && byUrl.has(resolved.url))\012"
+    "        return { url: resolved.url, format: \"module\", shortCircuit: true };\012"
+    "      return resolved;\012"
+    "    },\012"
+    "    load(url, context, nextLoad) {\012"
+    "      const mod = byUrl.get(url);\012"
+    "      if (mod !== undefined)\012"
+    "        return { format: \"module\", source: sharedSource(mod), shortCircuit: true };\012"
+    "      if (entries.has(url))\012"
+    "        return { format: \"module\", source: entrySource(url), shortCircuit: true };\012"
+    "      return nextLoad(url, context);\012"
+    "    },\012"
+    "  });\012"
+    "\012"
+    "  return {\012"
+    "    /** The entry to load the island module at `path` through, or null when\012"
+    "     * no shared binding is in its temporal dead zone. Run `load` with it. */\012"
+    "    entry(path, load) {\012"
+    "      const late = JSON.parse(nativeHost.sharedTdz());\012"
+    "      if (late.length === 0) return load(null);\012"
+    "      // A file URL beside the island module (never on disk: the load hook\012"
+    "      // answers it), so require() and import key it alike.\012"
+    "      const url = pathToFileURL(join(dirname(path), `__scriptc_entry_${++entrySeq}.mjs`)).href;\012"
+    "      entries.set(url, { target: pathToFileURL(path).href, late });\012"
+    "      const outer = current;\012"
+    "      current = url;\012"
+    "      try {\012"
+    "        return load(fileURLToPath(url));\012"
+    "      } finally {\012"
+    "        current = outer;\012"
+    "      }\012"
+    "    },\012"
+    "    push(mod, slot, value) {\012"
+    "      for (const set of setters.get(`${mod}:${slot}`) \077\077 []) set(value);\012"
+    "    },\012"
+    "  };\012"
+    "}\012";
 
 #endif /* SCR_NODE_ISLAND_HOST_H */
diff --git a/packages/runtime/test/node-island-host.test.ts b/packages/runtime/test/node-island-host.test.ts
index 3fe28697f..8867a161f 100644
--- a/packages/runtime/test/node-island-host.test.ts
+++ b/packages/runtime/test/node-island-host.test.ts
@@ -8,6 +8,6 @@ const srcDir = join(import.meta.dirname, "../src");
 // scr_node_island.c starts `node -e` with the host embedded in this header;
 // a host edit without regenerating it would ship the old host.
 test("the embedded Node island host matches its source", () => {
-  const source = readFileSync(join(srcDir, "scr_node_island_host.cjs"), "utf8");
+  const source = `${readFileSync(join(srcDir, "scr_node_island_host.cjs"), "utf8")}\n${readFileSync(join(srcDir, "scr_node_island_hooks.cjs"), "utf8")}`;
   expect(readFileSync(join(srcDir, "scr_node_island_host.h"), "utf8")).toBe(renderHeader(source));
 });
diff --git a/scripts/node-island-host.mjs b/scripts/node-island-host.mjs
index 61b93c411..3dadaf26d 100644
--- a/scripts/node-island-host.mjs
+++ b/scripts/node-island-host.mjs
@@ -10,6 +10,8 @@ import { fileURLToPath } from "node:url";
 
 const srcDir = fileURLToPath(new URL("../packages/runtime/src/", import.meta.url));
 const SOURCE = `${srcDir}scr_node_island_host.cjs`;
+// The loader hooks of shared modules (NI-6) run in the bootstrap's scope.
+const HOOKS = `${srcDir}scr_node_island_hooks.cjs`;
 const HEADER = `${srcDir}scr_node_island_host.h`;
 
 /** One C string literal per source line, every byte outside printable
@@ -28,7 +30,8 @@ export function renderHeader(source) {
   const lines = source.split("\n");
   if (lines.at(-1) === "") lines.pop();
   const body = lines.map((line) => `    ${cLiteral(`${line}\n`)}`).join("\n");
-  return `/* Generated by scripts/node-island-host.mjs from scr_node_island_host.cjs.
+  return `/* Generated by scripts/node-island-host.mjs from scr_node_island_host.cjs
+ * and scr_node_island_hooks.cjs.
  * Do not edit: change the .cjs file and rerun the script. */
 #ifndef SCR_NODE_ISLAND_HOST_H
 #define SCR_NODE_ISLAND_HOST_H
@@ -41,7 +44,7 @@ ${body};
 }
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const expected = renderHeader(readFileSync(SOURCE, "utf8"));
+  const expected = renderHeader(`${readFileSync(SOURCE, "utf8")}\n${readFileSync(HOOKS, "utf8")}`);
   if (process.argv.includes("--check")) {
     if (readFileSync(HEADER, "utf8") !== expected) {
       console.error(`${HEADER} is stale: run node scripts/node-island-host.mjs`);
diff --git a/tests/corpus/6811-node-island-uncaught-listener/island.cjs b/tests/corpus/6811-node-island-uncaught-listener/island.cjs
index 650c7f3f3..ae988f8c0 100644
--- a/tests/corpus/6811-node-island-uncaught-listener/island.cjs
+++ b/tests/corpus/6811-node-island-uncaught-listener/island.cjs
@@ -1,4 +1,4 @@
 exports.timers = () => {
-  setTimeout(() => console.log("island timer 1"), 15);
-  setTimeout(() => console.log("island timer 2"), 40);
+  setTimeout(() => console.log("island timer 1"), 150);
+  setTimeout(() => console.log("island timer 2"), 250);
 };
diff --git a/tests/corpus/6811-node-island-uncaught-listener/main.mjs b/tests/corpus/6811-node-island-uncaught-listener/main.mjs
index 9195e7baa..05397c2e4 100644
--- a/tests/corpus/6811-node-island-uncaught-listener/main.mjs
+++ b/tests/corpus/6811-node-island-uncaught-listener/main.mjs
@@ -7,12 +7,14 @@ import { callSync } from "@scriptc/node";
 process.on("uncaughtException", (error) => {
   console.log("caught", error.message);
 });
+// The island's timers (150 and 250 ms) are scheduled before these (10 and
+// 50 ms), with gaps wide enough that a slow run keeps the delay order.
 callSync("./island.cjs", "timers");
 setTimeout(() => {
   console.log("native timer throws");
   throw new Error("native boom");
-}, 5);
-setTimeout(() => console.log("native timer after"), 10);
+}, 10);
+setTimeout(() => console.log("native timer after"), 50);
 setImmediate(() => {
   queueMicrotask(() => {
     throw new Error("from a microtask");
diff --git a/tests/corpus/6850-node-island-shared-singleton/main.mjs b/tests/corpus/6850-node-island-shared-singleton/main.mjs
new file mode 100644
index 000000000..ec3b76256
--- /dev/null
+++ b/tests/corpus/6850-node-island-shared-singleton/main.mjs
@@ -0,0 +1,46 @@
+// @requires-libnode
+// A module both the program and a Node island import exists once (scope-B
+// NI-6): island imports of the compiled `state.mjs` resolve to its live
+// native exports, so a write on either side is seen by the other, and an
+// exported `let` is a live binding in the island too.
+import { requireModule } from "@scriptc/node";
+import { config, count, entries, record, reset, describe, retitle } from "./state.mjs";
+import { bumpTally, tally } from "./tally.mjs";
+
+record("main-1");
+console.log("main before island", count, entries());
+
+const plugin = requireModule("./plugin.mjs");
+console.log("island start:", plugin.startup);
+console.log("main after island load", count, entries());
+
+console.log("island report:", plugin.report());
+record("main-2");
+console.log("island report after main write:", plugin.report());
+console.log("island bump:", plugin.bump("island-2"), "main sees", count);
+
+plugin.configure("island-mode");
+console.log("main sees config", config.mode, config.owner);
+config.owner = "main";
+console.log("island sees config", plugin.describeConfig());
+
+console.log("same functions", plugin.sameRecord(record), plugin.requireSees());
+reset();
+console.log("after reset", count, entries(), plugin.report());
+
+// A module loaded straight into Node is the program's own instance, and
+// its members called as methods are the program's functions.
+const direct = requireModule("./state.mjs");
+const { record: directRecord, entries: directEntries } = direct;
+directRecord("direct-1");
+console.log("direct load", count, entries(), directEntries() === entries());
+console.log("direct methods", direct.record("direct-2"), direct.record(String(count + 1)), direct.entries());
+bumpTally();
+const { bumpTally: islandBump } = requireModule("./tally.mjs");
+console.log("tally", islandBump(), tally);
+
+// A reassigned exported function declaration is a live binding too: the
+// island sees the function the program installed.
+console.log("describe", plugin.describeNow(), describe());
+retitle();
+console.log("retitled", plugin.describeNow(), describe());
diff --git a/tests/corpus/6850-node-island-shared-singleton/plugin.mjs b/tests/corpus/6850-node-island-shared-singleton/plugin.mjs
new file mode 100644
index 000000000..3d73ed191
--- /dev/null
+++ b/tests/corpus/6850-node-island-shared-singleton/plugin.mjs
@@ -0,0 +1,41 @@
+// Island code (loaded with requireModule): imports the shared module by
+// named imports, by namespace, and through require().
+import { createRequire } from "node:module";
+import * as ns from "./state.mjs";
+import { config, count, entries, record, describe } from "./state.mjs";
+
+const require = createRequire(import.meta.url);
+
+record("island-1");
+export const startup = `count=${count} ns=${ns.count} entries=${entries()}`;
+
+export function report() {
+  return `count=${count} ns=${ns.count} entries=${entries()}`;
+}
+
+export function bump(name) {
+  const before = count;
+  const after = record(name);
+  return `${before}->${after} live=${count}`;
+}
+
+export function configure(mode) {
+  config.mode = mode;
+}
+
+export function describeConfig() {
+  return `${config.mode}/${config.owner}`;
+}
+
+export function sameRecord(fn) {
+  return fn === record && fn === ns.record;
+}
+
+export function requireSees() {
+  const viaRequire = require("./state.mjs");
+  return viaRequire === ns && viaRequire.entries() === entries();
+}
+
+export function describeNow() {
+  return describe();
+}
diff --git a/tests/corpus/6850-node-island-shared-singleton/state.mjs b/tests/corpus/6850-node-island-shared-singleton/state.mjs
new file mode 100644
index 000000000..0bbf8989c
--- /dev/null
+++ b/tests/corpus/6850-node-island-shared-singleton/state.mjs
@@ -0,0 +1,31 @@
+// @ts-nocheck -- reassigning the exported function declaration below is the
+// behavior under test; a checked file rejects the write.
+// A stateful singleton: a module-level log and an exported counter.
+export let count = 0;
+const log = [];
+export const config = { mode: "default", owner: "state" };
+
+export function record(entry) {
+  log.push(entry);
+  count++;
+  return count;
+}
+
+export function entries() {
+  return log.join(",");
+}
+
+export function reset() {
+  log.length = 0;
+  count = 0;
+}
+
+// A function declaration whose binding this module reassigns: its export
+// is live, like a `let` (a function declaration binds like `var`).
+export function describe() {
+  return "first";
+}
+
+export function retitle() {
+  describe = () => "second";
+}
diff --git a/tests/corpus/6850-node-island-shared-singleton/tally.mjs b/tests/corpus/6850-node-island-shared-singleton/tally.mjs
new file mode 100644
index 000000000..cf6a39af0
--- /dev/null
+++ b/tests/corpus/6850-node-island-shared-singleton/tally.mjs
@@ -0,0 +1,8 @@
+// A program module no island code imports, loaded into Node only through
+// requireModule(): it is still the program's one instance.
+export let tally = 0;
+
+export function bumpTally() {
+  tally++;
+  return tally;
+}
diff --git a/tests/corpus/6851-node-island-shared-class/island.mjs b/tests/corpus/6851-node-island-shared-class/island.mjs
new file mode 100644
index 000000000..6b36626b6
--- /dev/null
+++ b/tests/corpus/6851-node-island-shared-class/island.mjs
@@ -0,0 +1,35 @@
+import { Point, isPoint, make, remember, remembered } from "./shapes.mjs";
+
+export function check(p) {
+  return `${p instanceof Point} ${isPoint(p)} ${p.describe()} norm=${p.norm()}`;
+}
+
+export function create(x, y) {
+  return new Point(x, y);
+}
+
+export function selfCheck() {
+  const p = new Point(1, 1);
+  return `${p instanceof Point} ${isPoint(p)} ${make(2, 2) instanceof Point}`;
+}
+
+export function plainIsPoint() {
+  return `${{ x: 1 } instanceof Point} ${isPoint({ x: 1 })}`;
+}
+
+export function keep(p) {
+  return remember(p);
+}
+
+export function firstIsNative(p) {
+  return remembered(0) === p;
+}
+
+export function viaFactory() {
+  const p = make(5, 12);
+  return `${p.describe()} ${p.norm()} ${p instanceof Point}`;
+}
+
+export function sameClass(c) {
+  return c === Point;
+}
diff --git a/tests/corpus/6851-node-island-shared-class/main.mjs b/tests/corpus/6851-node-island-shared-class/main.mjs
new file mode 100644
index 000000000..600b107f9
--- /dev/null
+++ b/tests/corpus/6851-node-island-shared-class/main.mjs
@@ -0,0 +1,23 @@
+// @requires-libnode
+// A class exported by a module both sides import is one class (scope-B
+// NI-6): instances made on either side answer instanceof on both, keep
+// their identity, and their methods run natively.
+import { requireModule } from "@scriptc/node";
+import { Point, describeAll, isPoint, make, remember, remembered } from "./shapes.mjs";
+
+const island = requireModule("./island.mjs");
+
+const native = new Point(3, 4);
+console.log("island sees native instance:", island.check(native));
+const fromIsland = island.create(6, 8);
+console.log("native instanceof:", fromIsland instanceof Point, isPoint(fromIsland));
+console.log("native reads:", fromIsland.x, fromIsland.y, fromIsland.norm());
+console.log("island instanceof:", island.selfCheck());
+console.log("plain object (island):", island.plainIsPoint());
+console.log("plain object (native):", isPoint({ x: 1, y: 2 }));
+
+remember(native);
+console.log("kept:", island.keep(fromIsland), describeAll());
+console.log("identity:", remembered(1) === fromIsland, island.firstIsNative(native));
+console.log("made by native factory in island:", island.viaFactory());
+console.log("class identity:", island.sameClass(Point), island.sameClass(make));
diff --git a/tests/corpus/6851-node-island-shared-class/shapes.mjs b/tests/corpus/6851-node-island-shared-class/shapes.mjs
new file mode 100644
index 000000000..cdc5dc77d
--- /dev/null
+++ b/tests/corpus/6851-node-island-shared-class/shapes.mjs
@@ -0,0 +1,35 @@
+export class Point {
+  constructor(x, y) {
+    this.x = x;
+    this.y = y;
+  }
+  norm() {
+    return Math.hypot(this.x, this.y);
+  }
+  describe() {
+    return `(${this.x},${this.y})`;
+  }
+}
+
+const kept = [];
+
+export function remember(p) {
+  kept.push(p);
+  return kept.length;
+}
+
+export function remembered(i) {
+  return kept[i];
+}
+
+export function describeAll() {
+  return kept.map((p) => p.describe()).join(" ");
+}
+
+export function make(x, y) {
+  return new Point(x, y);
+}
+
+export function isPoint(p) {
+  return p instanceof Point;
+}
diff --git a/tests/corpus/6852-node-island-shared-cycle/main.mjs b/tests/corpus/6852-node-island-shared-cycle/main.mjs
new file mode 100644
index 000000000..adf916dd6
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/main.mjs
@@ -0,0 +1,10 @@
+// @requires-libnode
+// An import cycle through a Node island (scope-B NI-6): the compiled package
+// `core` imports the island package `ext`, which imports `core` back. As in
+// Node, `ext` evaluates first and sees core's functions (hoisted) but its
+// let and const bindings in their temporal dead zone; once core's body ran,
+// the same bindings read core's live values.
+import { check, x } from "core";
+
+console.log("main:", check());
+console.log("main x:", x);
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.d.ts b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.d.ts
new file mode 100644
index 000000000..4bd83c41b
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.d.ts
@@ -0,0 +1,5 @@
+export let x: number;
+export const y: string;
+export function f(): string;
+export function bump(): number;
+export function check(): string;
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.js b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.js
new file mode 100644
index 000000000..6c6a56662
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/index.js
@@ -0,0 +1,16 @@
+import { early, later, bumpFromIsland } from "ext";
+
+console.log("core body starts; ext saw:", early);
+export let x = 1;
+export const y = "y";
+export function f() {
+  return "f";
+}
+export function bump() {
+  x++;
+  return x;
+}
+export function check() {
+  return `${later()} ${bumpFromIsland()} ${later()}`;
+}
+
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/core/package.json b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/package.json
new file mode 100644
index 000000000..5bbd96010
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/core/package.json
@@ -0,0 +1 @@
+{ "name": "core", "version": "1.0.0", "type": "module", "main": "index.js", "types": "index.d.ts" }
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.d.ts b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.d.ts
new file mode 100644
index 000000000..c081053df
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.d.ts
@@ -0,0 +1,3 @@
+export const early: string;
+export function later(): string;
+export function bumpFromIsland(): string;
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.js b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.js
new file mode 100644
index 000000000..efff5b9ab
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/index.js
@@ -0,0 +1,19 @@
+import { bump, f, x, y } from "core";
+
+console.log("ext evaluates; f() =", f());
+function probe(read) {
+  try {
+    return String(read());
+  } catch (e) {
+    return `${e.name}: ${e.message}`;
+  }
+}
+export const early = `${probe(() => x)} | ${probe(() => y)}`;
+
+export function later() {
+  return `x=${x} y=${y}`;
+}
+
+export function bumpFromIsland() {
+  return `bump=${bump()} x=${x}`;
+}
diff --git a/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/package.json b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/package.json
new file mode 100644
index 000000000..1e44518e2
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/node_modules/ext/package.json
@@ -0,0 +1 @@
+{ "name": "ext", "version": "1.0.0", "type": "module", "main": "index.js", "types": "index.d.ts" }
diff --git a/tests/corpus/6852-node-island-shared-cycle/package.json b/tests/corpus/6852-node-island-shared-cycle/package.json
new file mode 100644
index 000000000..a026108b2
--- /dev/null
+++ b/tests/corpus/6852-node-island-shared-cycle/package.json
@@ -0,0 +1 @@
+{ "name": "shared-cycle", "private": true, "type": "module", "scriptc": { "packages": { "ext": "node" } } }
diff --git a/tests/corpus/6853-node-island-shared-registry/main.mjs b/tests/corpus/6853-node-island-shared-registry/main.mjs
new file mode 100644
index 000000000..060c11671
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/main.mjs
@@ -0,0 +1,21 @@
+// @requires-libnode
+// The registry scenario of the Node delegation design (§13): a stateful
+// package — a module-level Map, an exported `let counter`, a class — that
+// the program and a Node island both import. Island code subclasses the
+// package's class, so the package is shared Node-owned (scope-B NI-6): one
+// instance, its state visible on both sides, live bindings, `require` and
+// `import` answering the same module, instanceof both ways, and an island
+// subclass whose override and `super` call cross the boundary.
+import fs from "node:fs";
+import { requireModule } from "@scriptc/node";
+import * as reg from "registry";
+import { show } from "banner";
+
+const { run } = requireModule("./scenario.mjs");
+const log = (s) => fs.writeSync(1, `${s}\n`);
+reg.register(new reg.Plugin("owner-a"));
+run(log);
+log(`owner banner: ${show()}`);
+log(`owner list: ${reg.list().join(",")}`);
+log(`owner counter: ${reg.counter}`);
+log(`owner describeAll: ${reg.describeAll()}`);
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.d.ts b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.d.ts
new file mode 100644
index 000000000..aeff6941f
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.d.ts
@@ -0,0 +1,2 @@
+export declare const label: string;
+export declare function show(): string;
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.js b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.js
new file mode 100644
index 000000000..599d9b538
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/index.js
@@ -0,0 +1,6 @@
+// Looks pure (a const and a function), but its initializer prints: one
+// instance must evaluate it once.
+export const label = (console.log("banner loaded"), "B");
+export function show() {
+  return label;
+}
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/banner/package.json b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/package.json
new file mode 100644
index 000000000..4c0c8670b
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/banner/package.json
@@ -0,0 +1 @@
+{"name": "banner", "version": "1.0.0", "type": "module", "main": "index.js", "types": "index.d.ts"}
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.d.ts b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.d.ts
new file mode 100644
index 000000000..5c8096332
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.d.ts
@@ -0,0 +1,13 @@
+export let counter: number;
+export function bump(): number;
+export class Plugin {
+  name: string;
+  constructor(name: string);
+  describe(): string;
+}
+export function register(p: { name: string; describe(): string }): number;
+// A handle (NI-4 copies no island arrays into typed native arrays).
+export function list(): any;
+export function find(name: string): Plugin | undefined;
+export function describeAll(): string;
+export function noop<T>(x: T): T;
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.js b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.js
new file mode 100644
index 000000000..e66af40bc
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/index.js
@@ -0,0 +1,13 @@
+// A stateful singleton: a plugin registry with a mutable exported binding.
+export let counter = 0;
+export function bump() { return ++counter; }
+const items = new Map();
+export class Plugin {
+  constructor(name) { this.name = name; }
+  describe() { return `plugin:${this.name}`; }
+}
+export function register(p) { items.set(p.name, p); bump(); return items.size; }
+export function list() { return [...items.keys()]; }
+export function find(name) { return items.get(name); }
+export function describeAll() { return [...items.values()].map((p) => p.describe()).join(' | '); }
+export function noop(x) { return x; }
diff --git a/tests/corpus/6853-node-island-shared-registry/node_modules/registry/package.json b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/package.json
new file mode 100644
index 000000000..c47a4f064
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/node_modules/registry/package.json
@@ -0,0 +1 @@
+{ "name": "registry", "version": "1.0.0", "type": "module", "exports": { "types": "./index.d.ts", "default": "./index.js" } }
diff --git a/tests/corpus/6853-node-island-shared-registry/scenario.mjs b/tests/corpus/6853-node-island-shared-registry/scenario.mjs
new file mode 100644
index 000000000..6e3be0db7
--- /dev/null
+++ b/tests/corpus/6853-node-island-shared-registry/scenario.mjs
@@ -0,0 +1,28 @@
+// Island code. Imports the shared module both as ESM (named + namespace) and via require().
+import { createRequire } from 'node:module';
+import * as ns from 'registry';
+import { counter, bump, Plugin, register, list, find, describeAll, noop } from 'registry';
+import { show } from 'banner';
+const require = createRequire(import.meta.url);
+
+export function run(log) {
+  log(`island banner: ${show()}`);
+  log(`island list: ${list().join(',')}`);
+  log(`island counter: named=${counter} ns=${ns.counter}`);
+  bump();
+  log(`after island bump: named=${counter} ns=${ns.counter}`);
+  log(`require() sees same instance: ${require('registry').list().join(',')}`);
+  const p = new Plugin('island-b');
+  register(p);
+  log(`instanceof (island-constructed): ${p instanceof Plugin}`);
+  log(`instanceof (owner-constructed): ${find('owner-a') instanceof Plugin}`);
+  log(`find returns same object twice: ${find('owner-a') === find('owner-a')}`);
+  class Sub extends Plugin { describe() { return `sub(${super.describe()})`; } }
+  const sub = new Sub('island-sub');
+  log(`subclass: proto ok=${Object.getPrototypeOf(sub) === Sub.prototype} describe=${sub.describe()} instanceof Plugin=${sub instanceof Plugin}`);
+  register(sub);
+  register({ name: 'island-plain', describe() { return 'plain-from-island'; } });
+  log(`describeAll from island: ${describeAll()}`);
+  log(`Object.keys(owner object): ${Object.keys(find('owner-a') ?? {}).join(',')}`);
+}
+
diff --git a/tests/corpus/6854-node-island-shared-registry-native/main.mjs b/tests/corpus/6854-node-island-shared-registry-native/main.mjs
new file mode 100644
index 000000000..9937676d7
--- /dev/null
+++ b/tests/corpus/6854-node-island-shared-registry-native/main.mjs
@@ -0,0 +1,18 @@
+// @requires-libnode
+// The registry scenario of the Node delegation design (§13) with the
+// registry as a program module, shared through the loader hooks over its
+// native exports (scope-B NI-6): one instance, its state visible on both
+// sides, live bindings, `require` and `import` answering the same module,
+// instanceof both ways, and island objects in the native registry. (The
+// design's island subclass is in 6843, where the registry is Node-owned.)
+import fs from "node:fs";
+import { requireModule } from "@scriptc/node";
+import * as reg from "./registry.mjs";
+
+const { run } = requireModule("./scenario.mjs");
+const log = (s) => fs.writeSync(1, `${s}\n`);
+reg.register(new reg.Plugin("owner-a"));
+run(log);
+log(`owner list: ${reg.list().join(",")}`);
+log(`owner counter: ${reg.counter}`);
+log(`owner describeAll: ${reg.describeAll()}`);
diff --git a/tests/corpus/6854-node-island-shared-registry-native/registry.mjs b/tests/corpus/6854-node-island-shared-registry-native/registry.mjs
new file mode 100644
index 000000000..e66af40bc
--- /dev/null
+++ b/tests/corpus/6854-node-island-shared-registry-native/registry.mjs
@@ -0,0 +1,13 @@
+// A stateful singleton: a plugin registry with a mutable exported binding.
+export let counter = 0;
+export function bump() { return ++counter; }
+const items = new Map();
+export class Plugin {
+  constructor(name) { this.name = name; }
+  describe() { return `plugin:${this.name}`; }
+}
+export function register(p) { items.set(p.name, p); bump(); return items.size; }
+export function list() { return [...items.keys()]; }
+export function find(name) { return items.get(name); }
+export function describeAll() { return [...items.values()].map((p) => p.describe()).join(' | '); }
+export function noop(x) { return x; }
diff --git a/tests/corpus/6854-node-island-shared-registry-native/scenario.mjs b/tests/corpus/6854-node-island-shared-registry-native/scenario.mjs
new file mode 100644
index 000000000..da85c3ec1
--- /dev/null
+++ b/tests/corpus/6854-node-island-shared-registry-native/scenario.mjs
@@ -0,0 +1,22 @@
+// Island code. Imports the shared module both as ESM (named + namespace) and via require().
+import { createRequire } from 'node:module';
+import * as ns from './registry.mjs';
+import { counter, bump, Plugin, register, list, find, describeAll, noop } from './registry.mjs';
+const require = createRequire(import.meta.url);
+
+export function run(log) {
+  log(`island list: ${list().join(',')}`);
+  log(`island counter: named=${counter} ns=${ns.counter}`);
+  bump();
+  log(`after island bump: named=${counter} ns=${ns.counter}`);
+  log(`require() sees same instance: ${require('./registry.mjs').list().join(',')}`);
+  const p = new Plugin('island-b');
+  register(p);
+  log(`instanceof (island-constructed): ${p instanceof Plugin}`);
+  log(`instanceof (owner-constructed): ${find('owner-a') instanceof Plugin}`);
+  log(`find returns same object twice: ${find('owner-a') === find('owner-a')}`);
+  register({ name: 'island-plain', describe() { return 'plain-from-island'; } });
+  log(`describeAll from island: ${describeAll()}`);
+  log(`Object.keys(owner object): ${Object.keys(find('owner-a') ?? {}).join(',')}`);
+}
+
diff --git a/tests/corpus/8412-module-namespace-untyped/main.ts b/tests/corpus/8412-module-namespace-untyped/main.ts
new file mode 100644
index 000000000..fcb84a729
--- /dev/null
+++ b/tests/corpus/8412-module-namespace-untyped/main.ts
@@ -0,0 +1,77 @@
+// A module namespace taken as a checked-dynamic value: Node's export keys,
+// live reads, function typeof, member calls, `in`, for-in, JSON, the
+// [object Module] tag, the read-only write TypeErrors and the "Cannot
+// convert object to primitive value" coercion, plus `Promise<namespace>`
+// widening into `Promise<unknown>` and `unknown`.
+import * as declared from "./mod.ts";
+import * as expressionDefault from "./mod-default.ts";
+
+function keys(value: unknown): string {
+  return Object.keys(value as any).join(",");
+}
+
+function describe(value: unknown): void {
+  const dyn = value as any;
+  console.log("keys", keys(value));
+  console.log("kinds", valueKinds(value));
+  console.log("names", Object.getOwnPropertyNames(dyn).join(","));
+  console.log("alpha", dyn.alpha, typeof dyn.beta, typeof dyn.default);
+  console.log("call", dyn.beta());
+  console.log("tag", Object.prototype.toString.call(dyn));
+  console.log("in", "alpha" in dyn, "toString" in dyn);
+  const forIn: string[] = [];
+  for (const key in dyn) forIn.push(key);
+  console.log("for-in", forIn.join(","));
+  console.log("json", JSON.stringify(dyn));
+  try {
+    console.log("string", String(dyn));
+  } catch (error) {
+    console.log("string threw", (error as Error).message);
+  }
+  try {
+    dyn.alpha = 2;
+    console.log("write", dyn.alpha);
+  } catch (error) {
+    console.log("write threw", (error as Error).message);
+  }
+  try {
+    dyn.gamma = 2;
+    console.log("add", dyn.gamma);
+  } catch (error) {
+    console.log("add threw", (error as Error).message);
+  }
+  console.log("live", dyn.alpha);
+}
+
+function valueKinds(value: unknown): string {
+  const dyn = value as any;
+  const kinds: string[] = [];
+  for (const key of Object.keys(dyn)) kinds.push(typeof dyn[key]);
+  return kinds.join(",");
+}
+
+function bump(value: unknown): void {
+  const dyn = value as any;
+  dyn.bump();
+  console.log("after bump", dyn.count);
+}
+
+async function main(): Promise<void> {
+  // An expression default is snapshotted once by the export statement;
+  // the boxed namespace's `default` read answers that value, like Node.
+  const boxedDefault: unknown = expressionDefault;
+  const dynDefault = boxedDefault as any;
+  console.log("expression default", dynDefault.default, typeof dynDefault.default);
+  console.log("expression keys", keys(boxedDefault), expressionDefault.default);
+  describe(declared);
+  bump(declared);
+  const loaded = await import("./mod.ts");
+  console.log("same", loaded === declared);
+  describe(loaded);
+  const widened: Promise<unknown> | undefined = import("./mod.ts");
+  if (widened) console.log("widened", keys(await widened));
+  const boxed: unknown = import("./mod.ts");
+  console.log("unknown", keys(await boxed));
+}
+
+main();
diff --git a/tests/corpus/8412-module-namespace-untyped/mod-default.ts b/tests/corpus/8412-module-namespace-untyped/mod-default.ts
new file mode 100644
index 000000000..a0af818a4
--- /dev/null
+++ b/tests/corpus/8412-module-namespace-untyped/mod-default.ts
@@ -0,0 +1,4 @@
+// An EXPRESSION default (`export default <expr>`): Node evaluates the
+// expression once, at the export statement, and the namespace object's
+// `default` property answers that snapshotted value.
+export default 42;
diff --git a/tests/corpus/8412-module-namespace-untyped/mod.ts b/tests/corpus/8412-module-namespace-untyped/mod.ts
new file mode 100644
index 000000000..be7be7d4a
--- /dev/null
+++ b/tests/corpus/8412-module-namespace-untyped/mod.ts
@@ -0,0 +1,12 @@
+export const alpha = 1;
+export let count = 0;
+export function beta(): string {
+  return "b" + String(count);
+}
+export function bump(): void {
+  count += 1;
+}
+export const obj = { k: alpha };
+export default class Gamma {
+  readonly tag = "g";
+}
diff --git a/tests/corpus/dynamic-method-receiver-statements.mjs b/tests/corpus/dynamic-method-receiver-statements.mjs
new file mode 100644
index 000000000..80c125475
--- /dev/null
+++ b/tests/corpus/dynamic-method-receiver-statements.mjs
@@ -0,0 +1,46 @@
+// Untyped methods that return their receiver, called as statements on
+// receivers whose class is known: side effects, throws, overrides, and
+// results that are used.
+class Builder {
+  constructor() {
+    this.parts = [];
+    this.count = 0;
+  }
+  add(part) {
+    if (part === "") throw new TypeError("empty part");
+    this.parts.push(part);
+    this.count++;
+    return this;
+  }
+  reset() {
+    this.parts.length = 0;
+    return this;
+  }
+}
+class LoudBuilder extends Builder {
+  add(part) {
+    super.add(part.toUpperCase());
+    return this;
+  }
+}
+const b = new Builder();
+for (let i = 0; i < 1000; i++) {
+  b.add("p" + (i % 3));
+  if (i % 100 === 99) b.reset();
+}
+console.log(b.count, b.parts.join(","));
+b.add("x").add("y");
+const same = b.add("z");
+console.log(same === b, b.parts.join(","));
+try {
+  b.add("");
+} catch (e) {
+  console.log(e instanceof TypeError, e.message, b.count);
+}
+const loud = new LoudBuilder();
+loud.add("a");
+loud.add("b").add("c");
+console.log(loud.parts.join(","), loud.count, loud instanceof Builder);
+const builders = [new Builder(), new LoudBuilder()];
+for (const each of builders) each.add("q");
+console.log(builders.map((each) => each.parts.join("")).join("|"));
diff --git a/tests/corpus/shorthand-builtin-values.cjs b/tests/corpus/shorthand-builtin-values.cjs
new file mode 100644
index 000000000..eeee0ff4e
--- /dev/null
+++ b/tests/corpus/shorthand-builtin-values.cjs
@@ -0,0 +1,97 @@
+// A builtin global in a shorthand property (`{ Uint8Array }`) holds the
+// value the long form (`{ Uint8Array: Uint8Array }`) and a plain read hold.
+
+const short = {
+  Uint8Array,
+  Int8Array,
+  Uint8ClampedArray,
+  Uint16Array,
+  Int16Array,
+  Uint32Array,
+  Int32Array,
+  Float32Array,
+  Float64Array,
+  NaN,
+  Infinity,
+  String,
+  Number,
+  Boolean,
+  BigInt,
+  ArrayBuffer,
+  Array,
+  Map,
+  JSON,
+  Math,
+  encodeURIComponent,
+  decodeURI,
+  crypto,
+  Buffer,
+  fetch,
+  console,
+  setTimeout,
+};
+const long = {
+  Uint8Array: Uint8Array,
+  Int8Array: Int8Array,
+  Uint8ClampedArray: Uint8ClampedArray,
+  Uint16Array: Uint16Array,
+  Int16Array: Int16Array,
+  Uint32Array: Uint32Array,
+  Int32Array: Int32Array,
+  Float32Array: Float32Array,
+  Float64Array: Float64Array,
+  NaN: NaN,
+  Infinity: Infinity,
+  String: String,
+  Number: Number,
+  Boolean: Boolean,
+  BigInt: BigInt,
+  ArrayBuffer: ArrayBuffer,
+  Array: Array,
+  Map: Map,
+  JSON: JSON,
+  Math: Math,
+  encodeURIComponent: encodeURIComponent,
+  decodeURI: decodeURI,
+  crypto: crypto,
+  Buffer: Buffer,
+  fetch: fetch,
+  console: console,
+  setTimeout: setTimeout,
+};
+
+for (const key of Object.keys(long)) {
+  const same = Number.isNaN(long[key]) ? Number.isNaN(short[key]) : short[key] === long[key];
+  console.log(key, same, typeof short[key]);
+}
+console.log(short.Uint8Array === Uint8Array, short.Float64Array === Float64Array);
+console.log(Object.keys(short).length, Object.keys(short)[0], Object.keys(short)[9]);
+
+// The typed-array constructors construct and keep their names.
+const bytes = new short.Uint8Array([1, 2, 300]);
+console.log(bytes, bytes instanceof Uint8Array, short.Uint8Array.name, short.Int32Array.BYTES_PER_ELEMENT);
+console.log(new short.Float64Array(2).length, short.Int16Array.from([1, -2]));
+console.log(short.NaN !== short.NaN, short.Infinity > 1e308, -short.Infinity);
+
+// Shorthand destructuring from the global object reads the same values.
+function fromGlobal() {
+  const { Uint8Array, Float32Array, NaN, Infinity, Buffer } = globalThis;
+  return [Uint8Array === long.Uint8Array, Float32Array === long.Float32Array, Number.isNaN(NaN), Infinity, Buffer === long.Buffer];
+}
+console.log(fromGlobal());
+
+// A local binding with a builtin's name is the local.
+function shadowed() {
+  const Uint8Array = "local";
+  const NaN = 5;
+  return { Uint8Array, NaN };
+}
+console.log(shadowed());
+
+// The global object's NaN and Infinity are numbers, read or destructured.
+function numbersFromGlobal() {
+  const { NaN: notANumber, Infinity: infinite } = globalThis;
+  return [typeof notANumber, notANumber !== notANumber, infinite, infinite === Infinity];
+}
+console.log(typeof globalThis.NaN, globalThis.NaN !== globalThis.NaN, globalThis.Infinity, -globalThis.Infinity);
+console.log(numbersFromGlobal());
diff --git a/tests/corpus/shorthand-builtin-values.ts b/tests/corpus/shorthand-builtin-values.ts
new file mode 100644
index 000000000..ad943b56e
--- /dev/null
+++ b/tests/corpus/shorthand-builtin-values.ts
@@ -0,0 +1,51 @@
+// A builtin global in a shorthand property (`{ Uint8Array }`) holds the
+// value the long form (`{ Uint8Array: Uint8Array }`) holds.
+
+const short: Record<string, unknown> = {
+  Uint8Array,
+  Int8Array,
+  Uint8ClampedArray,
+  Uint16Array,
+  Int16Array,
+  Uint32Array,
+  Int32Array,
+  Float32Array,
+  Float64Array,
+  NaN,
+  Infinity,
+  String,
+  ArrayBuffer,
+  encodeURIComponent,
+};
+const long: Record<string, unknown> = {
+  Uint8Array: Uint8Array,
+  Int8Array: Int8Array,
+  Uint8ClampedArray: Uint8ClampedArray,
+  Uint16Array: Uint16Array,
+  Int16Array: Int16Array,
+  Uint32Array: Uint32Array,
+  Int32Array: Int32Array,
+  Float32Array: Float32Array,
+  Float64Array: Float64Array,
+  NaN: NaN,
+  Infinity: Infinity,
+  String: String,
+  ArrayBuffer: ArrayBuffer,
+  encodeURIComponent: encodeURIComponent,
+};
+
+for (const key of Object.keys(long)) {
+  const value = long[key];
+  const same =
+    typeof value === "number" && Number.isNaN(value)
+      ? Number.isNaN(short[key])
+      : short[key] === value;
+  console.log(key, same, typeof short[key]);
+}
+
+const numbers = { NaN, Infinity };
+console.log(numbers.NaN !== numbers.NaN, numbers.Infinity > 1e308, -numbers.Infinity);
+
+const ctors = { Uint8Array, Float64Array };
+const bytes = new ctors.Uint8Array([1, 2, 300]);
+console.log(bytes, ctors.Uint8Array.name, new ctors.Float64Array(3).length);
diff --git a/tests/fixtures/node-test/cases/mock-timers.ts b/tests/fixtures/node-test/cases/mock-timers.ts
index 1e5e5883f..c31b16aa1 100644
--- a/tests/fixtures/node-test/cases/mock-timers.ts
+++ b/tests/fixtures/node-test/cases/mock-timers.ts
@@ -271,21 +271,24 @@ describe("imports", () => {
   it("named and namespace imports keep the loop's timers", async (t) => {
     t.mock.timers.enable({ apis: ["setTimeout"] });
     const log: string[] = [];
+    // The three timers are real and scheduled one after another, so their
+    // delays are 100 ms apart: a slow run (a sanitized build on a busy
+    // machine) still sees them fire in delay order.
     await Promise.all([
-      sleep(5).then(() => {
+      sleep(300).then(() => {
         log.push("named promise");
       }),
       new Promise<void>((resolve) =>
         namedSetTimeout(() => {
           log.push("named");
           resolve();
-        }, 2),
+        }, 100),
       ),
       new Promise<void>((resolve) =>
         timersNamespace.setTimeout(() => {
           log.push("namespace");
           resolve();
-        }, 3),
+        }, 200),
       ),
     ]);
     t.mock.timers.tick(10);
diff --git a/tests/harness/corpus-costs/6850-node-island-shared-singleton/main.mjs.json b/tests/harness/corpus-costs/6850-node-island-shared-singleton/main.mjs.json
new file mode 100644
index 000000000..6fb6039dd
--- /dev/null
+++ b/tests/harness/corpus-costs/6850-node-island-shared-singleton/main.mjs.json
@@ -0,0 +1 @@
+{ "plain": 2500 }
diff --git a/tests/harness/corpus-costs/6851-node-island-shared-class/main.mjs.json b/tests/harness/corpus-costs/6851-node-island-shared-class/main.mjs.json
new file mode 100644
index 000000000..6fb6039dd
--- /dev/null
+++ b/tests/harness/corpus-costs/6851-node-island-shared-class/main.mjs.json
@@ -0,0 +1 @@
+{ "plain": 2500 }
diff --git a/tests/harness/corpus-costs/6852-node-island-shared-cycle/main.mjs.json b/tests/harness/corpus-costs/6852-node-island-shared-cycle/main.mjs.json
new file mode 100644
index 000000000..6fb6039dd
--- /dev/null
+++ b/tests/harness/corpus-costs/6852-node-island-shared-cycle/main.mjs.json
@@ -0,0 +1 @@
+{ "plain": 2500 }
diff --git a/tests/harness/corpus-costs/6853-node-island-shared-registry/main.mjs.json b/tests/harness/corpus-costs/6853-node-island-shared-registry/main.mjs.json
new file mode 100644
index 000000000..6fb6039dd
--- /dev/null
+++ b/tests/harness/corpus-costs/6853-node-island-shared-registry/main.mjs.json
@@ -0,0 +1 @@
+{ "plain": 2500 }
diff --git a/tests/harness/corpus-costs/6854-node-island-shared-registry-native/main.mjs.json b/tests/harness/corpus-costs/6854-node-island-shared-registry-native/main.mjs.json
new file mode 100644
index 000000000..6fb6039dd
--- /dev/null
+++ b/tests/harness/corpus-costs/6854-node-island-shared-registry-native/main.mjs.json
@@ -0,0 +1 @@
+{ "plain": 2500 }
diff --git a/tests/harness/corpus-costs/8412-module-namespace-untyped/main.ts.json b/tests/harness/corpus-costs/8412-module-namespace-untyped/main.ts.json
new file mode 100644
index 000000000..6a0493eb5
--- /dev/null
+++ b/tests/harness/corpus-costs/8412-module-namespace-untyped/main.ts.json
@@ -0,0 +1 @@
+{ "plain": 4451, "san": 57918 }
diff --git a/tests/harness/corpus-costs/shorthand-builtin-values.cjs.json b/tests/harness/corpus-costs/shorthand-builtin-values.cjs.json
new file mode 100644
index 000000000..74a3101e8
--- /dev/null
+++ b/tests/harness/corpus-costs/shorthand-builtin-values.cjs.json
@@ -0,0 +1 @@
+{ "plain": 3100, "san": 4000 }
diff --git a/tests/harness/corpus-costs/shorthand-builtin-values.ts.json b/tests/harness/corpus-costs/shorthand-builtin-values.ts.json
new file mode 100644
index 000000000..f71f3eb98
--- /dev/null
+++ b/tests/harness/corpus-costs/shorthand-builtin-values.ts.json
@@ -0,0 +1 @@
+{ "plain": 1800, "san": 2400 }
diff --git a/tests/harness/node-island-shared-sources.test.ts b/tests/harness/node-island-shared-sources.test.ts
new file mode 100644
index 000000000..bdf091193
--- /dev/null
+++ b/tests/harness/node-island-shared-sources.test.ts
@@ -0,0 +1,75 @@
+/* Which program modules a program shares with its Node islands, and what
+ * of them the executable carries (scope-B NI-6). Builds to IR only: no
+ * libnode is needed. */
+import { mkdirSync, mkdtempSync, readFileSync, realpathSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterAll, describe, expect, test } from "vitest";
+import { compile, type ir } from "@scriptc/compiler";
+
+// Outside any node_modules directory: a program there would be a package.
+const cacheDir = realpathSync(mkdtempSync(join(tmpdir(), "scriptc-island-shared-")));
+
+const MAIN = `import { requireModule } from "@scriptc/node";
+import { tally } from "./tally.mjs";
+const plugin = requireModule("./plugin.mjs");
+console.log(tally(), plugin.name);
+`;
+const TALLY = `// tally: internal counting rules
+let n = 0;
+export function tally() { return ++n; }
+`;
+
+async function irOf(name: string, plugin: string): Promise<ir.IrModule> {
+  const dir = join(cacheDir, name);
+  mkdirSync(dir, { recursive: true });
+  writeFileSync(join(dir, "main.mjs"), MAIN);
+  writeFileSync(join(dir, "tally.mjs"), TALLY);
+  writeFileSync(join(dir, "plugin.mjs"), plugin);
+  const result = await compile(join(dir, "main.mjs"), {
+    outputKind: "ir",
+    outPath: join(dir, "program.ir.json"),
+    outDir: dir,
+    backend: "llvm",
+  });
+  if (!result.ok)
+    throw new Error(result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"));
+  return JSON.parse(readFileSync(result.artifact.path, "utf8")) as ir.IrModule;
+}
+
+function sharedPaths(mod: ir.IrModule): string[] {
+  const out: string[] = [];
+  JSON.stringify(mod, (_k, v: unknown) => {
+    const o = v as { kind?: string; fn?: string; args?: { kind?: string; value?: string }[] };
+    if (o !== null && typeof o === "object" && o.kind === "libCall" && o.fn === "nodeIsland.share")
+      for (const a of o.args ?? [])
+        if (a.kind === "strLit" && a.value !== undefined) out.push(a.value);
+    return v;
+  });
+  return out;
+}
+
+afterAll(() => rmSync(cacheDir, { recursive: true, force: true }));
+
+describe("program modules shared with Node islands", () => {
+  test("a specifier in a comment of island code shares nothing", async () => {
+    const mod = await irOf(
+      "comment",
+      `// This plugin never imports "./tally.mjs": import { tally } from "./tally.mjs";\nexport const name = "plugin";\n`,
+    );
+    expect(sharedPaths(mod).some((p) => p.endsWith("tally.mjs"))).toBe(false);
+  });
+
+  test("a shared module's source stays out of the shipped tree", async () => {
+    const mod = await irOf(
+      "import",
+      `import { tally } from "./tally.mjs";\nexport const name = "plugin:" + tally();\n`,
+    );
+    expect(sharedPaths(mod).some((p) => p.endsWith("tally.mjs"))).toBe(true);
+    const tree = mod.nodeIsland?.modules;
+    expect(tree).toBeDefined();
+    const entry = tree!.files.find((f) => f.path.endsWith("tally.mjs"));
+    expect(entry?.placeholder).toBe(true);
+    expect(tree!.files.map((f) => f.path).sort()).toEqual(["plugin.mjs", "tally.mjs"]);
+  });
+});
diff --git a/tests/harness/node-island.test.ts b/tests/harness/node-island.test.ts
index 971311d75..ea4d3e6c1 100644
--- a/tests/harness/node-island.test.ts
+++ b/tests/harness/node-island.test.ts
@@ -308,7 +308,7 @@ describe.skipIf(skip)("Node islands in-process", () => {
     });
     expect(result.code).toBe(1);
     expect(result.stderr).toBe(
-      `scriptc: the libnode pack at ${dir} has an incompatible bridge (ABI 999; this program needs 6)\n`,
+      `scriptc: the libnode pack at ${dir} has an incompatible bridge (ABI 999; this program needs 7)\n`,
     );
   });
 
diff --git a/tests/harness/static-spatial.test.ts b/tests/harness/static-spatial.test.ts
index b0f40ee4e..e9bb23b1c 100644
--- a/tests/harness/static-spatial.test.ts
+++ b/tests/harness/static-spatial.test.ts
@@ -29,6 +29,9 @@ const cases = [
 ].flatMap((fixture) => ["native", "wasm32-wasi"].map((target) => ({ fixture, target })));
 test.for(cases)(
   "published $fixture runs statically on $target",
+  // Bundling three.js and building it with the sanitizer can pass the
+  // default 300 s on a busy runner, as in three.test.ts.
+  { timeout: 1_200_000 },
   async ({ fixture, target }, context) => {
     if (target === "wasm32-wasi" && !hasZig) context.skip();
     const dir = await mkdtemp("/tmp/scriptc-spatial-");