diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index fff1931ae..c697c699f 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -387,7 +387,7 @@ jobs:
       - name: Check version sync
         run: |
           VERSION="${{ needs.check-release.outputs.version }}"
-          for pkg in packages/runtime packages/runtime-* packages/llvm-* packages/compiler packages/experimental packages/threads packages/types packages/cli packages/cli-*; do
+          for pkg in packages/runtime packages/runtime-* packages/llvm-* packages/compiler packages/experimental packages/node packages/threads packages/types packages/cli packages/cli-*; do
             if [ "$(node -p "require('./$pkg/package.json').private === true")" = "true" ]; then
               continue
             fi
@@ -485,6 +485,7 @@ jobs:
           for pkg in packages/cli-*; do publish_dir "$pkg"; done
           publish_dir packages/compiler
           publish_dir packages/experimental
+          publish_dir packages/node
           publish_dir packages/threads
           publish_dir packages/types
           publish_dir packages/cli
diff --git a/RELEASING.md b/RELEASING.md
index 6cafe84a3..514f22429 100644
--- a/RELEASING.md
+++ b/RELEASING.md
@@ -1,11 +1,11 @@
 # Releasing
 
-Releases are manual, single-commit affairs. The maintainer controls the changelog voice and format. `@scriptc/runtime`, every platform helper/runtime pack, `@scriptc/compiler`, `@scriptc/experimental`, `@scriptc/threads`, and `scriptc` always publish together at the same version.
+Releases are manual, single-commit affairs. The maintainer controls the changelog voice and format. `@scriptc/runtime`, every platform helper/runtime pack, `@scriptc/compiler`, `@scriptc/experimental`, `@scriptc/node`, `@scriptc/threads`, and `scriptc` always publish together at the same version.
 
 To prepare a release:
 
 1. Bump the version in `packages/cli/package.json`
-2. Run `node scripts/sync-versions.mjs` to stamp the same version into the runtime, helper, compiler, experimental, and threads packages, then `pnpm manifest` to restamp `packages/compiler/surface-manifest.json` with the new version, and commit both (the test suite's staleness guard fails on a version drift)
+2. Run `node scripts/sync-versions.mjs` to stamp the same version into the runtime, helper, compiler, experimental, node, and threads packages, then `pnpm manifest` to restamp `packages/compiler/surface-manifest.json` with the new version, and commit both (the test suite's staleness guard fails on a version drift)
 3. Fold the `## Unreleased` section of `CHANGELOG.md` into a new `## <version>` entry (newest first, below `## Unreleased`), and leave `## Unreleased` empty for the next cycle
 4. Wrap the new entry in `<!-- release:start -->` and `<!-- release:end -->` markers; this marked block is also the GitHub release body
 5. Remove the `<!-- release:start -->` and `<!-- release:end -->` markers from the previous release entry; only the latest release should have markers
diff --git a/package.json b/package.json
index ff4c84dc2..88709a137 100644
--- a/package.json
+++ b/package.json
@@ -35,6 +35,7 @@
   },
   "devDependencies": {
     "@scriptc/experimental": "workspace:*",
+    "@scriptc/node": "workspace:*",
     "@scriptc/threads": "workspace:*",
     "@scriptc/types": "workspace:*",
     "@types/node": "^24.0.0",
diff --git a/packages/compiler/src/frontend/lowering/expressions/identifiers.ts b/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
index b5f99d682..6f13af366 100644
--- a/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
+++ b/packages/compiler/src/frontend/lowering/expressions/identifiers.ts
@@ -59,6 +59,7 @@ import {
 import { dirname } from "node:path";
 import { funcTypeFromParamShapes } from "../call-signatures.js";
 import { threadsImportOf } from "../../threads-import.js";
+import { nodeApiBindingOf } from "../../node-api-import.js";
 import { experimentalImportOf } from "../../experimental-import.js";
 import { lowerWorkerMetadata } from "../builtins/workers.js";
 import { esmImportBindingKind } from "../builtins/module-bindings.js";
@@ -460,6 +461,19 @@ export function lowerIdentifierExpr(lowerer: Lowerer, expr: ts.Identifier, loc:
         expr,
         "call publish(value) directly",
       );
+    const nodeApi = nodeApiBindingOf(lowerer.program, expr);
+    if (nodeApi === "namespace")
+      lowerer.noLowering(
+        "the @scriptc/node namespace as a value",
+        expr,
+        "call its call and callSync members directly",
+      );
+    if (nodeApi !== null)
+      lowerer.noLowering(
+        `${nodeApi} (@scriptc/node) as a value`,
+        expr,
+        `call ${nodeApi}(specifier, name, ...args) directly`,
+      );
     if (experimentalImportOf(lowerer.program, expr) === "LifetimeRegion")
       lowerer.noLowering(
         "LifetimeRegion (@scriptc/experimental) as a value",
diff --git a/packages/compiler/src/frontend/lowering/lower-calls.ts b/packages/compiler/src/frontend/lowering/lower-calls.ts
index d768cec9b..1f368e07f 100644
--- a/packages/compiler/src/frontend/lowering/lower-calls.ts
+++ b/packages/compiler/src/frontend/lowering/lower-calls.ts
@@ -14,6 +14,8 @@ import { lowerArrayCallbackCall } from "./containers/array-callback-call.js";
 import { dynUndefinedExpr, nodeThrowExpr, countedFor, numLit, varRef } from "../../ir/build.js";
 import { lowerBuiltinCall } from "./builtin-calls.js";
 import { threadsImportOf } from "../threads-import.js";
+import { nodeApiCalleeOf } from "../node-api-import.js";
+import { lowerNodeApiCall } from "./lower-node-island.js";
 import {
   adaptZeroArgTimerCallback,
   lowerTimersMemberCall,
@@ -286,6 +288,12 @@ export function lowerCall(lowerer: Lowerer, expr: ts.CallExpression): IrExpr {
     const codeGeneration = codeGenerationCalleeOf(lowerer, expr.expression);
     if (codeGeneration !== null) return lowerCodeGenerationCall(lowerer, expr, codeGeneration);
   }
+  // @scriptc/node call/callSync: a call into the Node island helper
+  // (lower-node-island.ts).
+  {
+    const nodeApi = nodeApiCalleeOf(lowerer.program, expr.expression);
+    if (nodeApi !== null) return lowerNodeApiCall(lowerer, expr, nodeApi);
+  }
   // Inline require() of a program module (cjs-inline-require.ts): a
   // member call over its export table resolves like a binding's member
   // call after the module's %init at this position; the require itself
diff --git a/packages/compiler/src/frontend/lowering/lower-modules.ts b/packages/compiler/src/frontend/lowering/lower-modules.ts
index 6ca21ddaa..5bd0a2800 100644
--- a/packages/compiler/src/frontend/lowering/lower-modules.ts
+++ b/packages/compiler/src/frontend/lowering/lower-modules.ts
@@ -1,4 +1,5 @@
 import { THREADS_MODULE } from "../threads-import.js";
+import { NODE_API_MODULE } from "../node-api-import.js";
 import { EXPERIMENTAL_MODULE } from "../experimental-import.js";
 import { dynUndefinedExpr } from "../../ir/build.js";
 import { everyStmtList, everyTypeChild } from "../../ir/traverse.js";
@@ -663,7 +664,12 @@ export function collectNpmImports(lowerer: Lowerer, parts: FileParts[]): void {
       // scriptc's own @scriptc/threads and @scriptc/experimental: their
       // exports lower at their use sites (threads-import.ts,
       // experimental-import.ts); their Node.js bodies never run.
-      if (npm?.packageName === THREADS_MODULE || npm?.packageName === EXPERIMENTAL_MODULE) continue;
+      if (
+        npm?.packageName === THREADS_MODULE ||
+        npm?.packageName === EXPERIMENTAL_MODULE ||
+        npm?.packageName === NODE_API_MODULE
+      )
+        continue;
       // An edge Node's RUNTIME resolution refuses at startup (types
       // resolved, but the exports target ships no JS — the types-only
       // package shape): preflight registered Node's startup crash for
diff --git a/packages/compiler/src/frontend/lowering/lower-node-island.ts b/packages/compiler/src/frontend/lowering/lower-node-island.ts
new file mode 100644
index 000000000..080a6862c
--- /dev/null
+++ b/packages/compiler/src/frontend/lowering/lower-node-island.ts
@@ -0,0 +1,129 @@
+/* Calls into Node islands. Milestone NI-1 of the scope-B plan has one kind:
+ * the explicit @scriptc/node API, `callSync(specifier, name, ...args)` and
+ * `call(...)`, which run an export of a module in Node.js loaded into the
+ * program (scr_node_island.c, libnode) and copy JSON data both ways. The
+ * libCalls are the only `nodeIsland.*` operations, so a program without
+ * them links none of that runtime (the `nodeIsland` runtime feature).
+ *
+ * Semantics, shared with packages/node/index.js (the Node implementation):
+ * the arguments are copied with JSON.stringify of the argument array; the
+ * module loads with require() from the calling module, so relative
+ * specifiers resolve from it; the result crosses as its JSON copy and is
+ * checked against the declared result type, like `JSON.parse(s) as T`; a
+ * thrown Error crosses as its nearest intrinsic class with its message and
+ * string `code`. */
+import { realpathSync } from "node:fs";
+import * as ts from "../ts7/adapter.js";
+import { locOf } from "../program.js";
+import type { NodeApiMember } from "../node-api-import.js";
+import { type Lowerer } from "./lowerer.js";
+import { DYN, STRING, type IrExpr, type IrType } from "../../ir/ir.js";
+
+const JSON_HINT =
+  "only JSON data (numbers, strings, booleans, null, arrays, plain objects of those, and unknown) crosses into Node.js in this version";
+
+/** The first part of `t` that is not JSON data, or null. `seen` holds the
+ * records and unions already being checked, so a recursive type (a JSON
+ * value type that contains arrays or records of itself) ends there. */
+function nonJsonPart(lowerer: Lowerer, t: IrType, seen: Set<string>): IrType | null {
+  switch (t.kind) {
+    case "f64":
+    case "string":
+    case "bool":
+    case "nullT":
+    case "undefinedT":
+    case "dyn":
+      return null;
+    case "array":
+      return nonJsonPart(lowerer, t.elem, seen);
+    case "record": {
+      if (seen.has(`record:${t.shapeId}`)) return null;
+      seen.add(`record:${t.shapeId}`);
+      const shape = lowerer.shapes.get(t.shapeId);
+      if (shape === undefined) return t;
+      for (const field of shape.fields) {
+        const bad = nonJsonPart(lowerer, field.type, seen);
+        if (bad !== null) return bad;
+      }
+      return shape.indexValue === undefined ? null : nonJsonPart(lowerer, shape.indexValue, seen);
+    }
+    case "union": {
+      if (seen.has(`union:${t.unionId}`)) return null;
+      seen.add(`union:${t.unionId}`);
+      const def = lowerer.unions.get(t.unionId);
+      if (def === undefined) return t;
+      for (const arm of def.arms) {
+        const bad = nonJsonPart(lowerer, arm, seen);
+        if (bad !== null) return bad;
+      }
+      return null;
+    }
+    default:
+      return t;
+  }
+}
+
+/** The calling module's real path: relative specifiers resolve from it,
+ * as Node's own loader resolves them from the real path of the module. */
+function callerPath(node: ts.Node): string {
+  const file = ts.getSourceFileOfNode(node).fileName;
+  try {
+    return realpathSync(file);
+  } catch {
+    return file;
+  }
+}
+
+export function lowerNodeApiCall(
+  lowerer: Lowerer,
+  call: ts.CallExpression,
+  member: NodeApiMember,
+): IrExpr {
+  const loc = locOf(call);
+  const surface = `${member} (@scriptc/node)`;
+  const argNodes = call.arguments.nodes;
+  if (call.questionDotToken || argNodes.length < 2 || argNodes.some(ts.isSpreadElement)) {
+    lowerer.noLowering(
+      `${surface} without a specifier and an export name, or with spread arguments`,
+      call,
+      "pass the module specifier, the export name and each argument explicitly",
+    );
+  }
+  const specifier = lowerer.lowerExprExpecting(argNodes[0]!, STRING);
+  const name = lowerer.lowerExprExpecting(argNodes[1]!, STRING);
+  const values = argNodes.slice(2).map((arg) => {
+    const value = lowerer.lowerExpr(arg);
+    const bad = nonJsonPart(lowerer, value.type, new Set());
+    if (bad !== null)
+      lowerer.noLowering(`passing '${lowerer.fmt(bad)}' values to ${surface}`, arg, JSON_HINT);
+    return lowerer.coerceToExpected(value, DYN);
+  });
+  const declared = lowerer.mapTypeOf(lowerer.typeOf(call));
+  const result = member === "call" && declared?.kind === "promise" ? declared.inner : declared;
+  if (declared === null || result === null || result === undefined) {
+    lowerer.noLowering(`${surface} with an unrepresentable result type`, call, JSON_HINT);
+  }
+  if (result.kind !== "void") {
+    const bad = nonJsonPart(lowerer, result, new Set());
+    if (bad !== null)
+      lowerer.noLowering(`'${lowerer.fmt(bad)}' results of ${surface}`, call, JSON_HINT);
+  }
+  lowerer.usesNodeIsland = true;
+  const raw: IrExpr = {
+    kind: "libCall",
+    fn: member === "call" ? "nodeIsland.call" : "nodeIsland.callSync",
+    args: [
+      { kind: "strLit", value: callerPath(call), type: STRING, loc },
+      specifier,
+      name,
+      { kind: "dynArrLit", elems: values, type: DYN, loc },
+    ],
+    type: member === "call" ? { kind: "promise", inner: DYN } : DYN,
+    loc,
+  };
+  // A void result is discarded, unchecked like any void call's value.
+  if (declared.kind === "void") return raw;
+  // The JSON copy meets the declared type through the checked boundary of
+  // `JSON.parse(s) as T`: types don't lie, a mismatch throws.
+  return lowerer.coerceToExpected(raw, declared);
+}
diff --git a/packages/compiler/src/frontend/lowering/lowerer.ts b/packages/compiler/src/frontend/lowering/lowerer.ts
index 543149f83..cdb738617 100644
--- a/packages/compiler/src/frontend/lowering/lowerer.ts
+++ b/packages/compiler/src/frontend/lowering/lowerer.ts
@@ -2937,6 +2937,9 @@ export class Lowerer {
   usesWasmCustomSections = false;
   /** The program constructs a LifetimeRegion (lifetime-regions.ts). */
   usesLifetimeRegions = false;
+  /** The program calls into Node.js (@scriptc/node): the module carries
+   * the nodeIsland record, which the executable build fills in. */
+  usesNodeIsland = false;
   /** 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. */
@@ -7285,6 +7288,7 @@ export class Lowerer {
             entry: ENTRY_NAME,
             ...(this.usesWorkers ? { workers: true } : {}),
             ...(this.usesLifetimeRegions ? { lifetimeRegions: true as const } : {}),
+            ...(this.usesNodeIsland ? { nodeIsland: { libnode: "", nodeVersion: "" } } : {}),
             ...(this.threadSlotKeys.size > 0
               ? { threadSlotKeys: [...this.threadSlotKeys].sort() }
               : {}),
diff --git a/packages/compiler/src/frontend/node-api-import.ts b/packages/compiler/src/frontend/node-api-import.ts
new file mode 100644
index 000000000..04db2489b
--- /dev/null
+++ b/packages/compiler/src/frontend/node-api-import.ts
@@ -0,0 +1,60 @@
+/* Provenance of the @scriptc/node exports. The package is scriptc's own
+ * (packages/node): Node.js runs its JavaScript implementation in-process,
+ * and scriptc builds lower its calls to calls into Node loaded into the
+ * program (lowering/lower-node-island.ts) and never compile its body. */
+import * as ts from "./ts7/adapter.js";
+
+export const NODE_API_MODULE = "@scriptc/node";
+
+export type NodeApiMember = "call" | "callSync";
+
+function moduleSpecifierText(decl: ts.Node | undefined): string | null {
+  return ts.isImportDeclaration(decl) && ts.isStringLiteral(decl.moduleSpecifier)
+    ? decl.moduleSpecifier.text
+    : null;
+}
+
+/** What an identifier binds from @scriptc/node: a named import of one of
+ * its functions, the namespace import (`import * as node`), or nothing. */
+export function nodeApiBindingOf(
+  program: ts.Program,
+  ident: ts.Identifier,
+): NodeApiMember | "namespace" | null {
+  const symbol = program.getTypeChecker().getSymbolAtLocation(ident);
+  const decl = symbol ? symbol.declarations[0] : undefined;
+  if (decl === undefined) return null;
+  if (ts.isNamespaceImport(decl))
+    return moduleSpecifierText(decl.parent?.parent) === NODE_API_MODULE ? "namespace" : null;
+  if (!ts.isImportSpecifier(decl)) return null;
+  if (moduleSpecifierText(decl.parent?.parent?.parent) !== NODE_API_MODULE) return null;
+  const member = decl.propertyName?.text ?? decl.name.text;
+  return member === "call" || member === "callSync" ? member : null;
+}
+
+/** The @scriptc/node export an identifier is a named-import binding of. */
+export function nodeApiImportOf(program: ts.Program, ident: ts.Identifier): NodeApiMember | null {
+  const binding = nodeApiBindingOf(program, ident);
+  return binding === "namespace" ? null : binding;
+}
+
+/** Whether an identifier is a namespace-import binding of @scriptc/node
+ * (`import * as node from "@scriptc/node"`). */
+export function isNodeApiNamespace(program: ts.Program, ident: ts.Identifier): boolean {
+  return nodeApiBindingOf(program, ident) === "namespace";
+}
+
+/** The @scriptc/node function a call's callee names: a named import
+ * (`callSync(...)`, also renamed) or a namespace member
+ * (`node.callSync(...)`). */
+export function nodeApiCalleeOf(program: ts.Program, callee: ts.Expression): NodeApiMember | null {
+  if (ts.isIdentifier(callee)) return nodeApiImportOf(program, callee);
+  if (
+    !ts.isPropertyAccessExpression(callee) ||
+    !ts.isIdentifier(callee.name) ||
+    !ts.isIdentifier(callee.expression)
+  )
+    return null;
+  const member = callee.name.text;
+  if (member !== "call" && member !== "callSync") return null;
+  return isNodeApiNamespace(program, callee.expression) ? member : null;
+}
diff --git a/packages/compiler/src/frontend/pipeline.ts b/packages/compiler/src/frontend/pipeline.ts
index 193e8adc0..cbd8c0cdd 100644
--- a/packages/compiler/src/frontend/pipeline.ts
+++ b/packages/compiler/src/frontend/pipeline.ts
@@ -44,6 +44,7 @@ import {
 import { moduleSourceCandidates } from "./module-source-candidates.js";
 import { CONTRACT_TYPES_MODULE } from "./contract-types.js";
 import { THREADS_MODULE } from "./threads-import.js";
+import { NODE_API_MODULE } from "./node-api-import.js";
 import { erasedTypeOnlyImport } from "./type-only-imports.js";
 import { EXPERIMENTAL_MODULE } from "./experimental-import.js";
 
@@ -251,7 +252,12 @@ function detectAutoPackages(
       // declarations only, and @scriptc/threads and @scriptc/experimental
       // exports lower at their use sites (threads-import.ts,
       // experimental-import.ts), typed by their declarations.
-      if (spec === CONTRACT_TYPES_MODULE || spec === THREADS_MODULE || spec === EXPERIMENTAL_MODULE)
+      if (
+        spec === CONTRACT_TYPES_MODULE ||
+        spec === THREADS_MODULE ||
+        spec === EXPERIMENTAL_MODULE ||
+        spec === NODE_API_MODULE
+      )
         continue;
       // Attested entries already resolve to program sources, so the
       // published package's declaration eligibility does not apply.
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6800-node-call-sync/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6800-node-call-sync/main.ts.json
new file mode 100644
index 000000000..94cb098e3
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6800-node-call-sync/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6800-node-call-sync/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6801-node-call-errors/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6801-node-call-errors/main.ts.json
new file mode 100644
index 000000000..3ee43a3a7
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6801-node-call-errors/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6801-node-call-errors/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6802-node-call-async/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6802-node-call-async/main.ts.json
new file mode 100644
index 000000000..675680664
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6802-node-call-async/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6802-node-call-async/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6803-node-call-exit/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6803-node-call-exit/main.ts.json
new file mode 100644
index 000000000..a835c1e1d
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6803-node-call-exit/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6803-node-call-exit/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/node/README.md b/packages/node/README.md
new file mode 100644
index 000000000..77002db49
--- /dev/null
+++ b/packages/node/README.md
@@ -0,0 +1,15 @@
+# @scriptc/node
+
+Call into Node.js from a scriptc program. `callSync` and `call` run a function exported by a JavaScript module and copy JSON data both ways. In scriptc builds the function runs in Node.js, which the program loads into its own process on the first call (libnode); under Node.js it runs directly, so the program prints the same either way.
+
+```ts
+import { call, callSync } from "@scriptc/node";
+
+const sum = callSync<number>("./math.cjs", "add", 1, 2);
+const config = await call<{ regions: string[] }>("config-parser", "parse", source);
+```
+
+- The module loads with `require()` from the calling module: relative specifiers resolve from its directory, bare ones from its `node_modules`.
+- Arguments and results cross as JSON copies; scriptc checks the result against the declared type.
+- A thrown `Error` crosses as its nearest intrinsic error class with its `message` and string `code`.
+- The executable loads Node from the libnode pack recorded at build time (`SCRIPTC_LIBNODE` or `scriptc build --libnode=<pack directory>`; `--libnode=beside` copies the pack next to the executable). `SCRIPTC_LIBNODE` overrides it at run time. A program that never calls into Node never loads it.
diff --git a/packages/node/index.d.ts b/packages/node/index.d.ts
new file mode 100644
index 000000000..10642b098
--- /dev/null
+++ b/packages/node/index.d.ts
@@ -0,0 +1,36 @@
+/** Calls the function `name` exported by the module `specifier` and returns
+ * its result.
+ *
+ * In scriptc builds the call runs in Node.js loaded into the program on
+ * the first call (the libnode pack recorded at build time, or
+ * SCRIPTC_LIBNODE). Under Node.js it runs in the same process too. Either
+ * way:
+ *
+ * - the module loads with require() from the calling module, so a relative
+ *   specifier resolves from the caller's directory and a bare one from its
+ *   node_modules (ES modules load through require(esm));
+ * - the arguments cross as a copy, `JSON.parse(JSON.stringify(args))`, and
+ *   the function runs with the module namespace as `this`;
+ * - the result crosses as its JSON copy (undefined stays undefined), and
+ *   scriptc checks it against `T` like `JSON.parse(text) as T`;
+ * - a thrown Error crosses as a new error of its nearest intrinsic class
+ *   (Error, TypeError, RangeError, SyntaxError, ReferenceError, EvalError,
+ *   URIError) with its message and string `code`; other thrown values cross
+ *   as JSON copies.
+ *
+ * A function that returns a promise cannot be called synchronously: the
+ * call throws a TypeError. Use {@link call}. */
+export declare function callSync<T = unknown>(
+  specifier: string,
+  name: string,
+  ...args: unknown[]
+): T;
+
+/** Like {@link callSync}, asynchronously: the function may return a
+ * promise, whose result is copied when it settles. The returned promise
+ * rejects instead of throwing, also when the arguments cannot be copied. */
+export declare function call<T = unknown>(
+  specifier: string,
+  name: string,
+  ...args: unknown[]
+): Promise<T>;
diff --git a/packages/node/index.js b/packages/node/index.js
new file mode 100644
index 000000000..ed5fd6870
--- /dev/null
+++ b/packages/node/index.js
@@ -0,0 +1,137 @@
+// @scriptc/node — the Node.js implementation.
+//
+// scriptc builds lower call() and callSync() to calls into Node.js loaded
+// into the program (packages/runtime/src/scr_node_island.c and its
+// bootstrap, scr_node_island_host.cjs). Under Node.js they run directly,
+// with the same copies at the boundary, so a program prints the same
+// either way. Keep the two in step: every message and copy rule here has
+// its twin in the bootstrap.
+
+import { createRequire } from "node:module";
+import { fileURLToPath } from "node:url";
+
+// Error classes that cross as copies, at the host's kind index.
+const ERROR_CLASSES = [
+  Error,
+  TypeError,
+  RangeError,
+  SyntaxError,
+  undefined,
+  ReferenceError,
+  EvalError,
+  URIError,
+];
+const ERROR_KINDS = [
+  [TypeError, 1],
+  [RangeError, 2],
+  [SyntaxError, 3],
+  [ReferenceError, 5],
+  [EvalError, 6],
+  [URIError, 7],
+];
+
+/** The file of the code that called `api`. */
+function callerFile(api) {
+  const savedPrepare = Error.prepareStackTrace;
+  const savedLimit = Error.stackTraceLimit;
+  let sites;
+  try {
+    Error.stackTraceLimit = 1;
+    Error.prepareStackTrace = (_error, callSites) => callSites;
+    const holder = {};
+    Error.captureStackTrace(holder, api);
+    sites = holder.stack;
+  } finally {
+    Error.prepareStackTrace = savedPrepare;
+    Error.stackTraceLimit = savedLimit;
+  }
+  const name = Array.isArray(sites) && sites.length > 0 ? sites[0].getFileName() : undefined;
+  if (typeof name !== "string")
+    throw new Error("@scriptc/node: cannot determine the calling module");
+  return name.startsWith("file:") ? fileURLToPath(name) : name;
+}
+
+const requires = new Map();
+
+function exportedFunction(file, specifier, name) {
+  let load = requires.get(file);
+  if (load === undefined) {
+    load = createRequire(file);
+    requires.set(file, load);
+  }
+  const namespace = load(specifier);
+  const fn = namespace === null || namespace === undefined ? undefined : namespace[name];
+  if (typeof fn !== "function")
+    throw new TypeError(`'${name}' exported by '${specifier}' is not a function`);
+  return { fn, namespace };
+}
+
+function isThenable(value) {
+  return (
+    value !== null &&
+    (typeof value === "object" || typeof value === "function") &&
+    typeof value.then === "function"
+  );
+}
+
+function errorKind(error) {
+  for (const [constructor, kind] of ERROR_KINDS) if (error instanceof constructor) return kind;
+  return 0;
+}
+
+/** The copy of a thrown value that the caller sees. */
+function copyThrown(error) {
+  if (error instanceof Error) {
+    const copy = new ERROR_CLASSES[errorKind(error)](String(error.message));
+    if (typeof error.code === "string") copy.code = error.code;
+    return copy;
+  }
+  let text;
+  try {
+    text = JSON.stringify(error);
+  } catch {
+    text = undefined;
+  }
+  return text === undefined ? undefined : JSON.parse(text);
+}
+
+/** The JSON copy of a result; throws what JSON.stringify throws. */
+function copyResult(value) {
+  const text = JSON.stringify(value);
+  return text === undefined ? undefined : JSON.parse(text);
+}
+
+function copyArgs(args) {
+  return JSON.parse(JSON.stringify(args));
+}
+
+export function callSync(specifier, name, ...args) {
+  const file = callerFile(callSync);
+  const copied = copyArgs(args);
+  let result;
+  try {
+    const { fn, namespace } = exportedFunction(file, specifier, name);
+    result = Reflect.apply(fn, namespace, copied);
+    if (isThenable(result)) {
+      // The promise is dropped: its rejection must not end the process.
+      Promise.resolve(result).catch(() => {});
+      throw new TypeError(
+        `callSync: '${name}' exported by '${specifier}' returned a promise; use call() for asynchronous functions`,
+      );
+    }
+    return copyResult(result);
+  } catch (error) {
+    throw copyThrown(error);
+  }
+}
+
+export async function call(specifier, name, ...args) {
+  const file = callerFile(call);
+  const copied = copyArgs(args);
+  try {
+    const { fn, namespace } = exportedFunction(file, specifier, name);
+    return copyResult(await Reflect.apply(fn, namespace, copied));
+  } catch (error) {
+    throw copyThrown(error);
+  }
+}
diff --git a/packages/node/package.json b/packages/node/package.json
new file mode 100644
index 000000000..6f588445a
--- /dev/null
+++ b/packages/node/package.json
@@ -0,0 +1,29 @@
+{
+  "name": "@scriptc/node",
+  "version": "0.4.1",
+  "description": "Call into Node.js from scriptc programs: run an export of a JavaScript module in a Node.js helper process and copy JSON data both ways. Under Node.js the calls run in-process.",
+  "license": "Apache-2.0",
+  "homepage": "https://scriptc.dev",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vercel-labs/scriptc.git",
+    "directory": "packages/node"
+  },
+  "type": "module",
+  "main": "index.js",
+  "types": "index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./index.d.ts",
+      "default": "./index.js"
+    }
+  },
+  "files": [
+    "index.js",
+    "index.d.ts",
+    "README.md"
+  ],
+  "engines": {
+    "node": ">=24.13.1"
+  }
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 3974f346e..b211b2e31 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -17,6 +17,9 @@ importers:
       '@scriptc/experimental':
         specifier: workspace:*
         version: link:packages/experimental
+      '@scriptc/node':
+        specifier: workspace:*
+        version: link:packages/node
       '@scriptc/threads':
         specifier: workspace:*
         version: link:packages/threads
@@ -191,6 +194,8 @@ importers:
 
   packages/llvm-win32-x64-msvc: {}
 
+  packages/node: {}
+
   packages/runtime: {}
 
   packages/runtime-android-arm64: {}
diff --git a/scripts/sync-versions.mjs b/scripts/sync-versions.mjs
index 044f812f9..57d6c4ec0 100644
--- a/scripts/sync-versions.mjs
+++ b/scripts/sync-versions.mjs
@@ -31,6 +31,7 @@ for (const pkg of [
   "runtime-android-arm64",
   "compiler",
   "experimental",
+  "node",
   "threads",
   "types",
   "cli-darwin-arm64",
diff --git a/tests/corpus/6800-node-call-sync/main.ts b/tests/corpus/6800-node-call-sync/main.ts
new file mode 100644
index 000000000..8f6f336ad
--- /dev/null
+++ b/tests/corpus/6800-node-call-sync/main.ts
@@ -0,0 +1,39 @@
+// @requires-libnode
+// Synchronous calls into Node.js through @scriptc/node: arguments and
+// results cross as JSON copies, module state lives on between calls, and
+// output from both sides interleaves in program order.
+import { callSync } from "@scriptc/node";
+import * as node from "@scriptc/node";
+import { callSync as runInNode } from "@scriptc/node";
+
+interface Point {
+  x: number;
+  y: number;
+  label: string;
+}
+
+console.log("before");
+const sum = callSync<number>("./math.cjs", "add", 2, 3);
+console.log("sum", sum, sum + 1);
+console.log(callSync<string>("./math.cjs", "greet", "wörld ☃ 🌍"));
+const p = callSync<Point>("./math.cjs", "point", 1.5, -2);
+console.log(p.x + p.y, p.label, JSON.stringify(p));
+const squares = callSync<number[]>("./math.cjs", "squares", 5);
+console.log(squares.length, squares.join(","));
+const nothing = callSync<undefined>("./math.cjs", "nothing");
+console.log(nothing === undefined);
+const echoed = callSync(
+  "./math.cjs",
+  "echo",
+  { a: [1, "two", null, true], b: { c: "d" } },
+  undefined,
+  [undefined, 0.1],
+);
+console.log(JSON.stringify(echoed));
+const flags = callSync<boolean[]>("./math.cjs", "flags", 3);
+console.log(flags.map((f) => (f ? "y" : "n")).join(""));
+console.log(node.callSync<string>("pkg-esm", "shout", "an es module, loaded with require"));
+console.log(runInNode<number>("./math.cjs", "add", 40, 2));
+console.log(callSync<number>("./math.cjs", "count"), callSync<number>("./math.cjs", "count"));
+callSync("./math.cjs", "say", "from node");
+console.log("after");
diff --git a/tests/corpus/6800-node-call-sync/math.cjs b/tests/corpus/6800-node-call-sync/math.cjs
new file mode 100644
index 000000000..dfdef5ffe
--- /dev/null
+++ b/tests/corpus/6800-node-call-sync/math.cjs
@@ -0,0 +1,13 @@
+"use strict";
+let calls = 0;
+exports.add = (a, b) => a + b;
+exports.greet = (name) => `hello, ${name}`;
+exports.point = (x, y) => ({ x, y, label: `(${x}, ${y})` });
+exports.squares = (n) => Array.from({ length: n }, (_, i) => i * i);
+exports.nothing = () => {};
+exports.echo = (...args) => args;
+exports.flags = (n) => Array.from({ length: n }, (_, i) => i % 2 === 0);
+exports.count = () => ++calls;
+exports.say = (text) => {
+  console.log(text);
+};
diff --git a/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/index.js b/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/index.js
new file mode 100644
index 000000000..bd890e132
--- /dev/null
+++ b/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/index.js
@@ -0,0 +1,3 @@
+export function shout(text) {
+  return `${text.toUpperCase()}!`;
+}
diff --git a/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/package.json b/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/package.json
new file mode 100644
index 000000000..b390c305d
--- /dev/null
+++ b/tests/corpus/6800-node-call-sync/node_modules/pkg-esm/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "pkg-esm",
+  "version": "1.0.0",
+  "type": "module",
+  "exports": "./index.js"
+}
diff --git a/tests/corpus/6801-node-call-errors/main.ts b/tests/corpus/6801-node-call-errors/main.ts
new file mode 100644
index 000000000..36064789b
--- /dev/null
+++ b/tests/corpus/6801-node-call-errors/main.ts
@@ -0,0 +1,45 @@
+// @requires-libnode
+// Errors thrown in Node.js cross into the program as copies: an Error as
+// its nearest intrinsic class with its message and string code, any other
+// thrown value as its JSON copy.
+import { callSync } from "@scriptc/node";
+
+function attempt(label: string, run: () => unknown): void {
+  try {
+    run();
+    console.log(label, "returned");
+  } catch (e) {
+    if (e instanceof Error) {
+      const code = (e as NodeJS.ErrnoException).code;
+      console.log(
+        label,
+        e.name,
+        e instanceof TypeError,
+        e instanceof RangeError,
+        JSON.stringify(e.message),
+        code ?? "-",
+      );
+    } else {
+      console.log(label, "value", JSON.stringify(e));
+    }
+  }
+}
+
+attempt("type", () => callSync("./throws.cjs", "typeError"));
+attempt("range", () => callSync("./throws.cjs", "rangeError"));
+attempt("syntax", () => callSync("./throws.cjs", "syntaxError"));
+attempt("coded", () => callSync("./throws.cjs", "coded"));
+attempt("custom class", () => callSync("./throws.cjs", "custom"));
+attempt("string", () => callSync("./throws.cjs", "string"));
+attempt("object", () => callSync("./throws.cjs", "object"));
+attempt("not a function", () => callSync("./throws.cjs", "notAFunction"));
+attempt("missing export", () => callSync("./throws.cjs", "missing"));
+attempt("promise", () => callSync("./throws.cjs", "later"));
+attempt("bigint result", () => callSync("./throws.cjs", "big"));
+attempt("returns", () => callSync("./throws.cjs", "fine"));
+try {
+  callSync("./does-not-exist.cjs", "anything");
+} catch (e) {
+  console.log("missing module", (e as NodeJS.ErrnoException).code);
+}
+console.log("done");
diff --git a/tests/corpus/6801-node-call-errors/throws.cjs b/tests/corpus/6801-node-call-errors/throws.cjs
new file mode 100644
index 000000000..98a3cf89f
--- /dev/null
+++ b/tests/corpus/6801-node-call-errors/throws.cjs
@@ -0,0 +1,32 @@
+"use strict";
+class ValidationError extends Error {
+  constructor(message) {
+    super(message);
+    this.name = "ValidationError";
+  }
+}
+exports.typeError = () => {
+  throw new TypeError("not a number: 'x'");
+};
+exports.rangeError = () => {
+  [].length = -1;
+};
+exports.syntaxError = () => JSON.parse("{oops");
+exports.coded = () => {
+  const error = new Error("no such thing");
+  error.code = "ENOTHING";
+  throw error;
+};
+exports.custom = () => {
+  throw new ValidationError("bad input");
+};
+exports.string = () => {
+  throw "boom";
+};
+exports.object = () => {
+  throw { reason: "nope", retry: false };
+};
+exports.notAFunction = 42;
+exports.later = () => Promise.reject(new Error("never seen"));
+exports.big = () => 10n;
+exports.fine = () => "ok";
diff --git a/tests/corpus/6802-node-call-async/main.ts b/tests/corpus/6802-node-call-async/main.ts
new file mode 100644
index 000000000..009d2da1f
--- /dev/null
+++ b/tests/corpus/6802-node-call-async/main.ts
@@ -0,0 +1,48 @@
+// @requires-libnode
+// Asynchronous calls into Node.js: results of promises cross when they
+// settle, rejections reject, and synchronous calls work while asynchronous
+// ones are outstanding and from promise reactions.
+import { call, callSync } from "@scriptc/node";
+
+interface Weather {
+  city: string;
+  temperature: number;
+  tags: string[];
+}
+
+async function main(): Promise<void> {
+  console.log("start");
+  const weather = await call<Weather>("./service.mjs", "weather", "Berlin");
+  console.log(weather.city, weather.temperature, weather.tags.join("+"));
+  console.log(await call<string>("./service.mjs", "slow", 20));
+  const doubled: number[] = await Promise.all([
+    call<number>("./service.mjs", "double", 1),
+    call<number>("./service.mjs", "double", 2),
+    call<number>("./service.mjs", "double", 3),
+  ]);
+  console.log(doubled.join(" "));
+  const pending = call<string>("./service.mjs", "slow", 30);
+  console.log("meanwhile", callSync<number>("./service.mjs", "plain", 7));
+  console.log(await pending);
+  await call<number>("./service.mjs", "double", 21).then((n) => {
+    console.log("then", n, callSync<number>("./service.mjs", "plain", n));
+  });
+  try {
+    await call("./service.mjs", "fails", "on purpose");
+  } catch (e) {
+    if (e instanceof Error)
+      console.log("rejected", e.name, e.message, (e as NodeJS.ErrnoException).code ?? "-");
+  }
+  try {
+    await call("./service.mjs", "missing");
+  } catch (e) {
+    if (e instanceof Error) console.log("rejected", e.name, e.message);
+  }
+  const nothing = await call<undefined>("./service.mjs", "nothing");
+  console.log(nothing === undefined);
+  // Node's own pending work keeps the program alive after main returns.
+  callSync("./service.mjs", "later", 15);
+  console.log("end");
+}
+
+main();
diff --git a/tests/corpus/6802-node-call-async/service.mjs b/tests/corpus/6802-node-call-async/service.mjs
new file mode 100644
index 000000000..568fa01a2
--- /dev/null
+++ b/tests/corpus/6802-node-call-async/service.mjs
@@ -0,0 +1,27 @@
+export function weather(city) {
+  return Promise.resolve({ city, temperature: 21.5, tags: ["sunny", "dry"] });
+}
+
+export function slow(ms) {
+  return new Promise((resolve) => setTimeout(() => resolve(`slept ${ms}`), ms));
+}
+
+export async function double(n) {
+  return n * 2;
+}
+
+export function plain(n) {
+  return n + 1;
+}
+
+export async function fails(why) {
+  const error = new RangeError(`failed ${why}`);
+  error.code = "ERR_FAILED";
+  throw error;
+}
+
+export async function nothing() {}
+
+export function later(ms) {
+  setTimeout(() => console.log(`island timer after ${ms} ms`), ms);
+}
diff --git a/tests/corpus/6803-node-call-exit/leave.cjs b/tests/corpus/6803-node-call-exit/leave.cjs
new file mode 100644
index 000000000..283f09baa
--- /dev/null
+++ b/tests/corpus/6803-node-call-exit/leave.cjs
@@ -0,0 +1,5 @@
+"use strict";
+exports.leave = (code) => {
+  console.log("leaving with", code);
+  process.exit(code);
+};
diff --git a/tests/corpus/6803-node-call-exit/main.ts b/tests/corpus/6803-node-call-exit/main.ts
new file mode 100644
index 000000000..4e19499be
--- /dev/null
+++ b/tests/corpus/6803-node-call-exit/main.ts
@@ -0,0 +1,12 @@
+// @exit: 3
+// @requires-libnode
+// process.exit in Node.js ends the whole program with its code, after the
+// program's own exit listeners ran.
+import { callSync } from "@scriptc/node";
+
+process.on("exit", (code) => {
+  console.log("exit listener", code);
+});
+console.log("before");
+callSync("./leave.cjs", "leave", 3);
+console.log("not reached");
diff --git a/tests/fixtures/node-island/helper.cjs b/tests/fixtures/node-island/helper.cjs
new file mode 100644
index 000000000..903532b0c
--- /dev/null
+++ b/tests/fixtures/node-island/helper.cjs
@@ -0,0 +1,3 @@
+"use strict";
+exports.answer = () => 42;
+exports.echo = (value) => value;
diff --git a/tests/fixtures/node-island/lifecycle.ts b/tests/fixtures/node-island/lifecycle.ts
new file mode 100644
index 000000000..f18ec640d
--- /dev/null
+++ b/tests/fixtures/node-island/lifecycle.ts
@@ -0,0 +1,19 @@
+// Loading Node on first use (tests/harness/node-island.test.ts): the
+// argument selects whether and how the program calls into Node.
+import { readFileSync } from "node:fs";
+import { callSync } from "@scriptc/node";
+
+const mode = process.argv[2] ?? "call";
+// Whether libnode is mapped into the process, from /proc/self/maps; other
+// platforms report "unknown".
+const mapped = (): boolean | string =>
+  process.platform === "linux"
+    ? readFileSync("/proc/self/maps", "utf8").includes("libnode")
+    : "unknown";
+console.log("mapped before", mapped());
+if (mode !== "never") {
+  console.log(callSync<number>("./helper.cjs", "answer"));
+  console.log("mapped after", mapped());
+}
+if (mode === "exit") process.exit(5);
+console.log("done");
diff --git a/tests/fixtures/node-island/package.json b/tests/fixtures/node-island/package.json
new file mode 100644
index 000000000..3dbc1ca59
--- /dev/null
+++ b/tests/fixtures/node-island/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/tests/fixtures/node-island/recursive-json.ts b/tests/fixtures/node-island/recursive-json.ts
new file mode 100644
index 000000000..90d9c757f
--- /dev/null
+++ b/tests/fixtures/node-island/recursive-json.ts
@@ -0,0 +1,9 @@
+// A recursive JSON value type as an argument and a result of a Node island
+// call (tests/harness/node-island.test.ts).
+import { callSync } from "@scriptc/node";
+
+type Json = number | string | boolean | null | Json[] | { [key: string]: Json };
+
+const input: Json = { list: [1, "two", [true, null]] };
+const output = callSync<Json>("./helper.cjs", "echo", input);
+console.log(JSON.stringify(output));
diff --git a/tests/harness/differential.test.ts b/tests/harness/differential.test.ts
index b70e59c86..3732f185e 100644
--- a/tests/harness/differential.test.ts
+++ b/tests/harness/differential.test.ts
@@ -23,6 +23,7 @@ import ts5 from "typescript";
 import { compile } from "@scriptc/compiler";
 import { corpusSelect, shardSuffix } from "./shard.js";
 import { oracleEnvKey } from "./oracle-env.js";
+import { libnodePack, requiresLibnode } from "./libnode.js";
 
 const execFileAsync = promisify(execFile);
 const repoRoot = join(import.meta.dirname, "../..");
@@ -405,7 +406,10 @@ describe(`differential corpus (${files.length} programs${sanitize ? ", sanitized
   test.for(files.map((f) => [f.slice(corpusDir.length + 1), f] as const))(
     "%s",
     { retry: 1 },
-    async ([, file]) => {
+    async ([, file], { skip }) => {
+      // `// @requires-libnode`: the binary loads Node from a libnode pack,
+      // required in the Linux CI lanes (libnode.ts), else skipped without one.
+      if (requiresLibnode(file) && libnodePack() === null) skip();
       const [nodeRes, nativeRes] = await Promise.all([runNode(file), compileAndRun(file)]);
       // Compare as bytes; decode only for the failure diff.
       if (!nodeRes.stdout.equals(nativeRes.stdout)) {
diff --git a/tests/harness/linux-differential.test.ts b/tests/harness/linux-differential.test.ts
index 9730623cd..24c86aed9 100644
--- a/tests/harness/linux-differential.test.ts
+++ b/tests/harness/linux-differential.test.ts
@@ -9,6 +9,7 @@ import { compile } from "@scriptc/compiler";
 import { npmCases } from "./npm-cases.js";
 import { normalizeNodeTestOutput } from "./node-test-normalize.js";
 import { eventLoopCases, type StdinScript } from "./event-loop-cases.js";
+import { requiresLibnode } from "./libnode.js";
 
 const execFileAsync = promisify(execFile);
 const enabled = process.env["SCRIPTC_LINUX"] === "1";
@@ -123,6 +124,9 @@ const files = enabled
     ])
       .sort()
       .filter((f) => filter === undefined || new RegExp(filter).test(f))
+      // Calls into Node load a libnode pack for the host, not for this
+      // cross target (libnode.ts).
+      .filter((f) => !requiresLibnode(f))
   : [];
 
 if (enabled) {
diff --git a/tests/harness/llvm-differential.test.ts b/tests/harness/llvm-differential.test.ts
index 792fdb1d2..390c1116a 100644
--- a/tests/harness/llvm-differential.test.ts
+++ b/tests/harness/llvm-differential.test.ts
@@ -11,6 +11,7 @@ import { describe, expect, test } from "vitest";
 import ts5 from "typescript";
 import { compile } from "@scriptc/compiler";
 import { corpusSelect, shardSuffix } from "./shard.js";
+import { libnodePack, requiresLibnode } from "./libnode.js";
 
 const execFileAsync = promisify(execFile);
 const repoRoot = join(import.meta.dirname, "../..");
@@ -192,7 +193,9 @@ async function build(file: string, optimization: "release" | "dev") {
 describe(`llvm differential corpus (${files.length} programs, ${optimizationModes.join("+")}${sanitize ? ", sanitized" : ""}${shardSuffix()})`, () => {
   test.for(files.map((f) => [f.slice(corpusDir.length + 1), f] as const))(
     "%s",
-    async ([rel, file]) => {
+    async ([rel, file], { skip }) => {
+      // Programs that call into Node need a libnode pack (libnode.ts).
+      if (requiresLibnode(file) && libnodePack() === null) skip();
       const oracle = await runBinary(process.execPath, nodeOracleArgs(file));
       const expectedExit = expectedExitCode(file);
       expect(oracle.exitCode).toBe(expectedExit);
diff --git a/tests/harness/node-island.test.ts b/tests/harness/node-island.test.ts
new file mode 100644
index 000000000..47a68e290
--- /dev/null
+++ b/tests/harness/node-island.test.ts
@@ -0,0 +1,208 @@
+/* Node islands loaded in-process (scope-B milestone NI-1), where it cannot
+ * be a differential corpus program: a run that never calls into Node never
+ * maps libnode, the beside packaging carries its own pack, a missing or
+ * mismatched pack fails the first call with a message, and the executable
+ * links no Node and exports nothing libnode could bind to. The corpus
+ * (6800-6803) pins the call semantics against Node. Needs a libnode pack
+ * in SCRIPTC_LIBNODE; required in the Linux x64 CI lanes (libnode.ts). */
+import { execFile } from "node:child_process";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { promisify } from "node:util";
+import { beforeAll, describe, expect, test } from "vitest";
+import { compile, deserializeModule } from "@scriptc/compiler";
+import { definedFunctionNames, nodeIslandSymbols } from "../../scripts/zero-cost-compare.mjs";
+import { libnodePack } from "./libnode.js";
+
+const execFileAsync = promisify(execFile);
+const repoRoot = join(import.meta.dirname, "../..");
+const fixture = join(repoRoot, "tests/fixtures/node-island/lifecycle.ts");
+const outDir = join(repoRoot, "node_modules/.cache/scriptc-tests/node-island");
+const sanitize = process.env["SCRIPTC_SAN"] === "1";
+// Required in the Linux x64 CI lanes, where a missing pack fails here.
+const pack = libnodePack();
+const skip = pack === null;
+
+interface Run {
+  stdout: string;
+  stderr: string;
+  code: number | null;
+}
+
+let binary = "";
+
+// The fixture reads whether libnode is mapped from /proc/self/maps; other
+// platforms print "unknown".
+const before = `mapped before ${process.platform === "linux" ? "false" : "unknown"}`;
+const after = `mapped after ${process.platform === "linux" ? "true" : "unknown"}`;
+
+async function run(
+  path: string,
+  args: string[],
+  env: NodeJS.ProcessEnv = process.env,
+): Promise<Run> {
+  try {
+    const { stdout, stderr } = await execFileAsync(path, args, { env, encoding: "utf8" });
+    return { stdout, stderr: comparable(stderr), code: 0 };
+  } catch (err) {
+    const e = err as { stdout?: string; stderr?: string; code?: unknown };
+    if (typeof e.code !== "number") throw err;
+    return { stdout: e.stdout ?? "", stderr: comparable(e.stderr ?? ""), code: e.code };
+  }
+}
+
+/** Linux ASan's once-per-process warning at the first context switch (the
+ * switch to Node's stack), dropped as differential.test.ts drops it. */
+function comparable(stderr: string): string {
+  if (!sanitize) return stderr;
+  return stderr
+    .split("\n")
+    .filter((l) => !/^==\d+==WARNING: ASan doesn't fully support makecontext\/swapcontext/.test(l))
+    .join("\n");
+}
+
+async function build(name: string, libnode?: string): Promise<string> {
+  const dir = join(outDir, name);
+  mkdirSync(dir, { recursive: true });
+  const result = await compile(fixture, {
+    outPath: join(dir, "lifecycle"),
+    outDir: dir,
+    sanitize,
+    ...(libnode === undefined ? {} : { libnode }),
+  });
+  if (!result.ok)
+    throw new Error(result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"));
+  return result.binaryPath;
+}
+
+/** A bridge library that answers the ABI handshake and nothing else. */
+async function fakePack(name: string, abi: string, version: string): Promise<string> {
+  const dir = join(outDir, name);
+  mkdirSync(dir, { recursive: true });
+  const source = join(dir, "fake-bridge.c");
+  writeFileSync(
+    source,
+    `#include "scr_node_bridge.h"
+static const ScrNodeBridge bridge = {${abi}, "${version}", 127};
+__attribute__((visibility("default"))) const ScrNodeBridge *scr_node_bridge_v1(void) { return &bridge; }
+`,
+  );
+  const library =
+    process.platform === "darwin" ? "libscr_node_bridge.dylib" : "libscr_node_bridge.so";
+  await execFileAsync("clang", [
+    "-shared",
+    "-fPIC",
+    "-I",
+    join(repoRoot, "packages/runtime/src"),
+    source,
+    "-o",
+    join(dir, library),
+  ]);
+  return dir;
+}
+
+describe.skipIf(skip)("Node islands in-process", () => {
+  beforeAll(async () => {
+    binary = await build("recorded");
+  }, 300_000);
+
+  test("loads Node on the first call, and only then", async () => {
+    expect(await run(binary, [])).toEqual({
+      stdout: `${before}\n42\n${after}\ndone\n`,
+      stderr: "",
+      code: 0,
+    });
+    expect(await run(binary, ["never"])).toEqual({
+      stdout: `${before}\ndone\n`,
+      stderr: "",
+      code: 0,
+    });
+  });
+
+  test("process.exit after loading Node keeps its code", async () => {
+    const result = await run(binary, ["exit"]);
+    expect(result.code).toBe(5);
+    expect(result.stdout).toBe(`${before}\n42\n${after}\n`);
+  });
+
+  test("beside packaging carries its own pack", async () => {
+    const beside = await build("beside", "beside");
+    expect(existsSync(join(outDir, "beside/lifecycle.libnode/manifest.json"))).toBe(true);
+    const env = { ...process.env };
+    delete env["SCRIPTC_LIBNODE"];
+    const result = await run(beside, [], env);
+    expect(result.stdout).toBe(`${before}\n42\n${after}\ndone\n`);
+    expect(result.code).toBe(0);
+  }, 300_000);
+
+  test("a missing pack fails the first call", async () => {
+    const result = await run(binary, [], { ...process.env, SCRIPTC_LIBNODE: "/nonexistent/pack" });
+    expect(result.code).toBe(1);
+    expect(result.stdout).toBe(`${before}\n`);
+    expect(result.stderr).toMatch(
+      /^scriptc: cannot load Node\.js for this program's Node islands: .*\/nonexistent\/pack\/libscr_node_bridge\.(so|dylib).*\n$/,
+    );
+  });
+
+  test("a pack of another Node version fails the first call", async () => {
+    const dir = await fakePack("old-node", "SCR_NODE_BRIDGE_ABI", "22.11.0");
+    const result = await run(binary, [], { ...process.env, SCRIPTC_LIBNODE: dir });
+    expect(result.code).toBe(1);
+    expect(result.stderr).toMatch(
+      new RegExp(
+        `^scriptc: this program's Node islands need libnode \\d+\\.\\d+\\.\\d+; found 22\\.11\\.0 \\(NODE_MODULE_VERSION 127\\) at ${dir}\\n$`,
+      ),
+    );
+  });
+
+  test("a bridge of another ABI fails the first call", async () => {
+    const dir = await fakePack("other-abi", "999u", "24.22.0");
+    const result = await run(binary, [], { ...process.env, SCRIPTC_LIBNODE: dir });
+    expect(result.code).toBe(1);
+    expect(result.stderr).toBe(
+      `scriptc: the libnode pack at ${dir} has an incompatible bridge (ABI 999; this program needs 2)\n`,
+    );
+  });
+
+  test("links no Node and exports nothing libnode binds to", async () => {
+    if (process.platform !== "linux" || sanitize) return;
+    const { stdout } = await execFileAsync("nm", [binary], {
+      encoding: "utf8",
+      maxBuffer: 1 << 28,
+    });
+    const defined = definedFunctionNames(stdout);
+    expect(nodeIslandSymbols(defined)).toContain("scr_node_island_call_sync");
+    expect(defined.filter((name) => /^(napi_|_ZN2v8|_ZN4node|uv_)/.test(name))).toEqual([]);
+    // libnode joins the global scope (RTLD_GLOBAL): the executable must not
+    // export a name it would bind to instead of its own.
+    const dynamic = await execFileAsync("nm", ["-D", "--defined-only", binary], {
+      encoding: "utf8",
+    });
+    const conflicting = dynamic.stdout
+      .split("\n")
+      .map((line) => line.trim().split(/\s+/).at(-1) ?? "")
+      .filter((name) =>
+        /^(napi_|node_|uv_|_ZN2v8|_ZN4node|SSL|EVP_|ERR_|deflate|inflate|crc32|adler32|mbedtls_|ares_|nghttp2_)/.test(
+          name,
+        ),
+      );
+    expect(conflicting).toEqual([]);
+  });
+});
+
+// Lowering checks every argument and result type for JSON data; IR output
+// needs no libnode pack.
+test("recursive JSON types cross into Node", async () => {
+  const dir = join(outDir, "recursive-json");
+  mkdirSync(dir, { recursive: true });
+  const outPath = join(dir, "main.ir.json");
+  const result = await compile(join(repoRoot, "tests/fixtures/node-island/recursive-json.ts"), {
+    outPath,
+    outDir: dir,
+    outputKind: "ir",
+  });
+  if (!result.ok)
+    throw new Error(result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"));
+  const ir = JSON.stringify(deserializeModule(readFileSync(outPath, "utf8")));
+  expect(ir).toContain("nodeIsland.callSync");
+}, 300_000);
diff --git a/tests/harness/windows-differential.test.ts b/tests/harness/windows-differential.test.ts
index 366820420..87b8b162a 100644
--- a/tests/harness/windows-differential.test.ts
+++ b/tests/harness/windows-differential.test.ts
@@ -52,6 +52,7 @@ import { promisify } from "node:util";
 import { afterAll, beforeAll, describe, expect, test } from "vitest";
 import ts5 from "typescript";
 import { compile } from "@scriptc/compiler";
+import { requiresLibnode } from "./libnode.js";
 
 const execFileAsync = promisify(execFile);
 const enabled = process.env["SCRIPTC_WIN"] === "1";
@@ -265,6 +266,9 @@ const files = enabled
     ])
       .sort()
       .filter((f) => filter === undefined || new RegExp(filter).test(f))
+      // Calls into Node load a libnode pack for the host, not for this
+      // cross target (libnode.ts).
+      .filter((f) => !requiresLibnode(f))
   : [];
 
 if (enabled) {