diff --git a/packages/compiler/src/frontend/lowering/lower-classes.ts b/packages/compiler/src/frontend/lowering/lower-classes.ts
index 16760e061..17bc4f7ac 100644
--- a/packages/compiler/src/frontend/lowering/lower-classes.ts
+++ b/packages/compiler/src/frontend/lowering/lower-classes.ts
@@ -4362,6 +4362,7 @@ export function lowerStaticFieldInits(lowerer: Lowerer, info: ClassInfo): IrStmt
   // instantiation's bindings/context (a no-op for everything else —
   // generic FAMILIES own their statics and carry no genericInstance).
   const diagsBefore = lowerer.diags.length;
+  const sinkMark = lowerer.diagSinkMark();
   try {
     return withInstanceBindings(lowerer, info, () => lowerStaticFieldInitsInner(lowerer, info));
   } catch (error) {
@@ -4369,8 +4370,11 @@ export function lowerStaticFieldInits(lowerer: Lowerer, info: ClassInfo): IrStmt
     // Keep their refusal attached to the class declaration instead of
     // letting a poisoned initializer escape the module lowering pass.
     if (!(error instanceof PoisonError)) throw error;
-    if (info.decl && isJsSourceFile(info.decl.getSourceFile()) && lowerer.diagSink === null) {
-      const fence = lowerer.deferToRuntimeFence(diagsBefore, info.decl, { kind: "statement" });
+    if (info.decl && isJsSourceFile(info.decl.getSourceFile())) {
+      const fence =
+        lowerer.diagSink === null
+          ? lowerer.deferToRuntimeFence(diagsBefore, info.decl, { kind: "statement" })
+          : lowerer.capturedRuntimeFence(sinkMark, info.decl);
       if (fence) return [fence];
     }
     return [];
@@ -4507,6 +4511,7 @@ function lowerStaticFieldInitsInner(lowerer: Lowerer, info: ClassInfo): IrStmt[]
     lowerer.stats.statementsTotal++;
     lowerer.bumpFileStat(locOf(f.initializer).file, "total");
     const diagsBefore = lowerer.diags.length;
+    const sinkMark = lowerer.diagSinkMark();
     try {
       const previousThis = lowerer.ctx.thisLocal;
       const receiver =
@@ -4542,10 +4547,11 @@ function lowerStaticFieldInitsInner(lowerer: Lowerer, info: ClassInfo): IrStmt[]
       if (!(e instanceof PoisonError)) throw e;
       lowerer.stats.statementsFailed++;
       lowerer.bumpFileStat(locOf(f.initializer).file, "failed");
-      if (isJsSourceFile(f.initializer.getSourceFile()) && lowerer.diagSink === null) {
-        const fence = lowerer.deferToRuntimeFence(diagsBefore, f.initializer, {
-          kind: "statement",
-        });
+      if (isJsSourceFile(f.initializer.getSourceFile())) {
+        const fence =
+          lowerer.diagSink === null
+            ? lowerer.deferToRuntimeFence(diagsBefore, f.initializer, { kind: "statement" })
+            : lowerer.capturedRuntimeFence(sinkMark, f.initializer);
         if (fence) out.push(fence);
       }
     }
@@ -7619,6 +7625,7 @@ export function fieldInitStmts(lowerer: Lowerer, info: ClassInfo, thisLocal: IrL
     lowerer.stats.statementsTotal++;
     lowerer.bumpFileStat(locOf(f.initializer).file, "total");
     const diagsBefore = lowerer.diags.length;
+    const sinkMark = lowerer.diagSinkMark();
     try {
       const value = lowerer.lowerExprExpecting(f.initializer, f.type);
       out.push({
@@ -7633,10 +7640,11 @@ export function fieldInitStmts(lowerer: Lowerer, info: ClassInfo, thisLocal: IrL
       if (!(e instanceof PoisonError)) throw e;
       lowerer.stats.statementsFailed++;
       lowerer.bumpFileStat(locOf(f.initializer).file, "failed");
-      if (isJsSourceFile(f.initializer.getSourceFile()) && lowerer.diagSink === null) {
-        const fence = lowerer.deferToRuntimeFence(diagsBefore, f.initializer, {
-          kind: "statement",
-        });
+      if (isJsSourceFile(f.initializer.getSourceFile())) {
+        const fence =
+          lowerer.diagSink === null
+            ? lowerer.deferToRuntimeFence(diagsBefore, f.initializer, { kind: "statement" })
+            : lowerer.capturedRuntimeFence(sinkMark, f.initializer);
         if (fence) out.push(fence);
       }
     }
diff --git a/packages/compiler/src/frontend/lowering/lower-stmts.ts b/packages/compiler/src/frontend/lowering/lower-stmts.ts
index 0f1b606ef..f35df085c 100644
--- a/packages/compiler/src/frontend/lowering/lower-stmts.ts
+++ b/packages/compiler/src/frontend/lowering/lower-stmts.ts
@@ -672,6 +672,7 @@ export function lowerStmts(lowerer: Lowerer, stmts: readonly ts.Statement[]): Ir
         if (sf !== undefined) lowerer.bumpFileStat(sf.fileName, "total");
       }
       const diagsBefore = lowerer.diags.length;
+      const sinkMark = lowerer.diagSinkMark();
       try {
         let lowered: IrStmt | IrStmt[] | null;
         let appended = false;
@@ -756,6 +757,11 @@ export function lowerStmts(lowerer: Lowerer, stmts: readonly ts.Statement[]): Ir
             },
           });
           if (fence) out.push(fence);
+        } else if (deferFences) {
+          // Inside a capture buffer the owner keeps the diagnostics, but
+          // the statement still must not vanish from a result it keeps.
+          const fence = lowerer.capturedRuntimeFence(sinkMark, stmt);
+          if (fence) out.push(fence);
         }
       }
     }
diff --git a/packages/compiler/src/frontend/lowering/lowerer.ts b/packages/compiler/src/frontend/lowering/lowerer.ts
index 3c6cfe962..f71047de8 100644
--- a/packages/compiler/src/frontend/lowering/lowerer.ts
+++ b/packages/compiler/src/frontend/lowering/lowerer.ts
@@ -7194,23 +7194,8 @@ export class Lowerer {
     }
     this.runtimeFences.push(...captured);
 
-    const first = captured[0];
+    const fence = this.runtimeFenceStmt(captured[0], node, target.fallback, target.bareMessage);
     const loc = locOf(node);
-    const code = first?.code ?? target.fallback!.code;
-    const baseMessage = first?.message ?? target.fallback!.message;
-    const messageLoc = first?.loc ?? loc;
-    const source = first
-      ? (this.program.getSourceFile(messageLoc.file) ?? node.getSourceFile())
-      : node.getSourceFile();
-    const pos = ts.getLineAndCharacterOfPosition(source, messageLoc.start);
-    const fence: IrStmt = {
-      kind: "runtimeFence",
-      code,
-      message: target.bareMessage
-        ? baseMessage
-        : `${baseMessage} [${code} at ${messageLoc.file}:${pos.line + 1}]`,
-      loc,
-    };
     if (target.kind === "statement") return fence;
 
     const params = target.params ?? [];
@@ -7238,6 +7223,54 @@ export class Lowerer {
     return { kind: "closure", fnName: fn.name, captures: [], type: target.type, loc };
   }
 
+  /** The runtimeFence statement that throws `first`'s message (or the
+   * fallback's) at `node`. */
+  private runtimeFenceStmt(
+    first: ScrDiagnostic | undefined,
+    node: ts.Node,
+    fallback: { code: string; message: string } | undefined,
+    bareMessage = false,
+  ): IrStmt & { kind: "runtimeFence" } {
+    const loc = locOf(node);
+    const code = first?.code ?? fallback?.code ?? "SC1090";
+    const baseMessage =
+      first?.message ??
+      fallback?.message ??
+      "this statement uses a construct with no static lowering";
+    const messageLoc = first?.loc ?? loc;
+    const source = first
+      ? (this.program.getSourceFile(messageLoc.file) ?? node.getSourceFile())
+      : node.getSourceFile();
+    const pos = ts.getLineAndCharacterOfPosition(source, messageLoc.start);
+    return {
+      kind: "runtimeFence",
+      code,
+      message: bareMessage
+        ? baseMessage
+        : `${baseMessage} [${code} at ${messageLoc.file}:${pos.line + 1}]`,
+      loc,
+    };
+  }
+
+  /** The current length of the capture buffer (diagSink), or 0 without one:
+   * the mark capturedRuntimeFence reads the refusal from. */
+  diagSinkMark(): number {
+    return this.diagSink?.length ?? 0;
+  }
+
+  /** The runtimeFence for a JavaScript statement refused while a capture
+   * buffer (diagSink) is active. The buffer's owner decides whether its
+   * diagnostics report, and some owners keep the lowered result (a
+   * successful tryLowerExpression candidate, a computed class base whose
+   * diagnostics defer to the class). Without a fence the refused statement
+   * would vanish from that result; with one it throws the refusal when it
+   * runs, exactly like the fence lowerStmts emits outside a buffer. The
+   * diagnostics stay in the buffer for its owner. Null without a buffer. */
+  capturedRuntimeFence(sinkMark: number, node: ts.Node): IrStmt | null {
+    if (this.diagSink === null) return null;
+    return this.runtimeFenceStmt(this.diagSink[sinkMark], node, undefined);
+  }
+
   /** All diagnostics land here; while a generic instance body is lowering,
    * the instantiation context is appended so the user knows which concrete
    * types made the (source-anchored) construct fail. */
@@ -9872,27 +9905,21 @@ export class Lowerer {
    * instance type. Collection and body lowering own a refusal of that
    * class: the poison reaches the declaration or statement that asked, as
    * before. A speculative whole-program analysis owns none, so there the
-   * class is unmappable for the query and its diagnostics are dropped;
-   * lowering the class's own declaration collects it again and reports
-   * them if the program reaches it. */
+   * refusal stays reported (the build fails with it, as it did where such
+   * an analysis already caught the poison) and the class is unmappable for
+   * the query instead of the poison escaping the compiler. */
   collectLocalClassForType(decl: ts.ClassLikeDeclaration): boolean {
     if (this.speculativeTypeQueryDepth === 0 || this.fnStack.length > 0) {
       this.lowerClassExpressionInfo(decl);
       return true;
     }
-    const sink: ScrDiagnostic[] = [];
-    const previousSink = this.diagSink;
-    this.diagSink = sink;
     try {
       this.lowerClassExpressionInfo(decl);
+      return true;
     } catch (e) {
       if (e instanceof PoisonError) return false;
       throw e;
-    } finally {
-      this.diagSink = previousSink;
     }
-    for (const d of sink) this.pushDiag(d);
-    return true;
   }
 
   lowerClassExpression(expr: ts.ClassLikeDeclaration): IrExpr {
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6102-local-class-type-query.js.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6102-local-class-type-query.js.json
deleted file mode 100644
index 86c6ba9e8..000000000
--- a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6102-local-class-type-query.js.json
+++ /dev/null
@@ -1,6 +0,0 @@
-{
- "order": [
-  "<repo>/tests/corpus/6102-local-class-type-query.js"
- ],
- "diags": []
-}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs.json
new file mode 100644
index 000000000..0a5ce66b0
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/local-class-type-query-js.js.json b/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/local-class-type-query-js.js.json
new file mode 100644
index 000000000..6bf774cd8
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/local-class-type-query-js.js.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/diagnostics/local-class-type-query-js.js"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/speculative-function-refusal.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/speculative-function-refusal.ts.json
new file mode 100644
index 000000000..e24349766
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/diagnostics/speculative-function-refusal.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/diagnostics/speculative-function-refusal.ts"
+ ],
+ "diags": []
+}
diff --git a/tests/corpus/6102-local-class-type-query.js b/tests/corpus/6102-local-class-type-query.js
deleted file mode 100644
index 92fe35725..000000000
--- a/tests/corpus/6102-local-class-type-query.js
+++ /dev/null
@@ -1,42 +0,0 @@
-// A whole-program analysis that queries types before reachability is known
-// (the computed-key write census here) can name a function-local class whose
-// collection is refused. That query has no owner for the refusal: the class
-// stays unmapped for it, and the refusal belongs to the class's own
-// declaration, which this program never executes (it used to crash the
-// compiler with an uncaught PoisonError).
-function main(run) {
-  if (!run) return "skipped";
-  const Project = class {
-    constructor() {
-      this.name = "p";
-    }
-    close() {
-      if (this.missingFilesMap) {
-        this.missingFilesMap.clear();
-        this.missingFilesMap = void 0;
-      }
-    }
-    add(k) {
-      (this.missingFilesMap || (this.missingFilesMap = new Map())).set(k, 1);
-    }
-  };
-  const holder = { p: new Project() };
-  const key = String(run);
-  holder.p[key] = "q";
-  return holder.p.name;
-}
-
-class Counter {
-  constructor() {
-    this.counts = {};
-  }
-  bump(key) {
-    this.counts[key] = (this.counts[key] || 0) + 1;
-    return this.counts[key];
-  }
-}
-
-const counter = new Counter();
-const word = process.argv.length > 99 ? "unused" : "word";
-counter.bump(word);
-console.log(main(0), counter.bump(word));
diff --git a/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs b/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs
new file mode 100644
index 000000000..6040f009c
--- /dev/null
+++ b/tests/corpus/6110-cjs-speculative-wrapper-fences.cjs
@@ -0,0 +1,27 @@
+// @deferred-fences: 9
+// Function expressions lowered speculatively — the `.call(this)` and
+// `.apply` receivers of CommonJS wrappers, and a computed class base — keep
+// every statement of their bodies. A statement with no static lowering
+// (here `module.exports` read as a value) compiles to its runtime fence
+// instead of vanishing; these never run, so the binary matches Node.
+const verbose = process.argv.length > 99;
+(function () {
+  var root = this;
+  console.log("call wrapper");
+  if (verbose) console.log(root === module.exports);
+  console.log("call wrapper done");
+}).call(this);
+(function (label) {
+  console.log("apply wrapper", label);
+  if (verbose) console.log(typeof module.exports);
+}).apply(null, ["ok"]);
+class Base {
+  hello() {
+    return "hello";
+  }
+}
+class Derived extends (function () {
+  if (verbose) console.log(module.exports);
+  return Base;
+})() {}
+console.log(new Derived().hello());
diff --git a/tests/diagnostics/local-class-type-query-js.js b/tests/diagnostics/local-class-type-query-js.js
new file mode 100644
index 000000000..2da619133
--- /dev/null
+++ b/tests/diagnostics/local-class-type-query-js.js
@@ -0,0 +1,26 @@
+// A whole-program analysis that queries types before reachability is known
+// (the computed-key write census here, through `holder.p`) names a
+// function-local class whose collection is refused. The refusal is reported,
+// once, at the class; it used to crash the compiler with an uncaught
+// PoisonError.
+function main() {
+  const Project = class _Project {
+    constructor() {
+      this.name = "p";
+    }
+    close() {
+      if (this.missingFilesMap) {
+        this.missingFilesMap.clear();
+        this.missingFilesMap = void 0;
+      }
+    }
+    add(k) {
+      (this.missingFilesMap || (this.missingFilesMap = new Map())).set(k, 1);
+    }
+  };
+  const holder = { p: new Project() };
+  const key = process.argv.length > 5 ? String(process.argv.length) : "name";
+  holder.p[key] = "q";
+  console.log(holder.p.name);
+}
+main();
diff --git a/tests/diagnostics/speculative-function-refusal.ts b/tests/diagnostics/speculative-function-refusal.ts
new file mode 100644
index 000000000..fc48d9935
--- /dev/null
+++ b/tests/diagnostics/speculative-function-refusal.ts
@@ -0,0 +1,14 @@
+// Function expressions lowered speculatively — an `.apply` receiver and a
+// computed class base — report a refused statement in their body like any
+// other function: the statement never disappears from the build.
+(function () {
+  console.log("wrapper");
+  console.log(eval("1 + 1"));
+}).apply(null, []);
+
+class Base {}
+class Derived extends (function () {
+  console.log(new Function("return 1")());
+  return Base;
+})() {}
+console.log(typeof Derived);
diff --git a/tests/harness/__snapshots__/local-class-type-query-js.js.txt b/tests/harness/__snapshots__/local-class-type-query-js.js.txt
new file mode 100644
index 000000000..60422a5dc
--- /dev/null
+++ b/tests/harness/__snapshots__/local-class-type-query-js.js.txt
@@ -0,0 +1,6 @@
+local-class-type-query-js.js:14:9 - error SC1090: fields assigned outside the constructor's top level ('this.missingFilesMap' would be undefined until the first assignment runs — assign it unconditionally at the top of the constructor) is not supported yet
+
+  13 |         this.missingFilesMap.clear();
+  14 |         this.missingFilesMap = void 0;
+     |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  15 |       }
\ No newline at end of file
diff --git a/tests/harness/__snapshots__/speculative-function-refusal.ts.txt b/tests/harness/__snapshots__/speculative-function-refusal.ts.txt
new file mode 100644
index 000000000..c8b0cd28c
--- /dev/null
+++ b/tests/harness/__snapshots__/speculative-function-refusal.ts.txt
@@ -0,0 +1,17 @@
+speculative-function-refusal.ts:6:15 - error SC2020: 'eval' is part of the standard library types but has no scriptc lowering yet
+
+  5 |   console.log("wrapper");
+  6 |   console.log(eval("1 + 1"));
+    |               ^~~~
+  7 | }).apply(null, []);
+
+  hint: runtime code evaluation cannot be compiled ahead of time
+
+speculative-function-refusal.ts:11:15 - error SC2020: 'new Function' is part of the standard library types but has no scriptc lowering yet
+
+  10 | class Derived extends (function () {
+  11 |   console.log(new Function("return 1")());
+     |               ^~~~~~~~~~~~~~~~~~~~~~~~
+  12 |   return Base;
+
+  hint: runtime code generation cannot be compiled ahead of time (the eval stance) — write the function
\ No newline at end of file
diff --git a/tests/harness/corpus-costs.json b/tests/harness/corpus-costs.json
index f04b08154..5eeb6ffc8 100644
--- a/tests/harness/corpus-costs.json
+++ b/tests/harness/corpus-costs.json
@@ -2210,7 +2210,6 @@
     "605-closures-forward-capture-tdz.ts": 3277,
     "6100-record-get-or-create.ts": 3771,
     "6101-record-get-or-create-unchecked/main.ts": 2107,
-    "6102-local-class-type-query.js": 2600,
     "6103-typeof-builtin-bindings.cjs": 2202,
     "6104-typeof-builtin-bindings.mjs": 2031,
     "6105-cjs-top-level-this/main.js": 1371,
@@ -5258,7 +5257,6 @@
     "605-closures-forward-capture-tdz.ts": 4638,
     "6100-record-get-or-create.ts": 3173,
     "6101-record-get-or-create-unchecked/main.ts": 3228,
-    "6102-local-class-type-query.js": 1967,
     "6103-typeof-builtin-bindings.cjs": 1796,
     "6104-typeof-builtin-bindings.mjs": 1715,
     "6105-cjs-top-level-this/main.js": 3213,
diff --git a/tests/harness/errors.test.ts b/tests/harness/errors.test.ts
index 28daa88d3..51f04d310 100644
--- a/tests/harness/errors.test.ts
+++ b/tests/harness/errors.test.ts
@@ -960,3 +960,56 @@ for (const input of [ciphertext, Buffer.from("forged data"), Buffer.alloc(0)]) {
     expect(r.stderr).toBe("");
   });
 });
+
+// Function expressions the frontend lowers speculatively (the receiver of
+// `.call`/`.apply`, a computed class base) keep their refused statements as
+// runtime fences. They used to vanish: the capture buffer held the refusal,
+// the candidate was kept, and the statement was simply missing from it.
+describe("refused statements in speculatively lowered JavaScript functions", () => {
+  test.each([
+    [
+      "speculative-call-this",
+      `(function () {
+  var root = this;
+  console.log("before");
+  console.log(root === module.exports);
+  console.log("after");
+}).call(this);
+`,
+      "before\n",
+      4,
+    ],
+    [
+      "speculative-apply",
+      `(function () {
+  console.log("before");
+  console.log(typeof module.exports);
+}).apply(null, []);
+`,
+      "before\n",
+      3,
+    ],
+    [
+      "speculative-class-base",
+      `class Base {}
+class Derived extends (function () {
+  console.log("before");
+  console.log(typeof module.exports);
+  return Base;
+})() {}
+console.log(typeof Derived);
+`,
+      "before\n",
+      4,
+    ],
+  ] as const)("%s", async (name, source, stdout, line) => {
+    const r = await compileAndRun(name, source, "cjs");
+    expect(r.exitCode).toBe(1);
+    expect(r.stdout).toBe(stdout);
+    expect(r.stderr).toMatch(
+      new RegExp(
+        `^Uncaught Error: 'module\\.exports' is part of the standard library types but has no scriptc lowering yet \\[SC2020 at .*${name}\\.cjs:${line}\\]\\n$`,
+      ),
+    );
+  });
+});
diff --git a/tests/harness/npm.test.ts b/tests/harness/npm.test.ts
index ad10a25f4..976f9c525 100644
--- a/tests/harness/npm.test.ts
+++ b/tests/harness/npm.test.ts
@@ -73,7 +73,7 @@ const KNOWN: Record<string, Known> = {
   "node24-env": { run: "SC1090" },
   "node24-esm-metadata": { run: "SC1090" },
   "node24-event-emitter": { run: "SC2020" },
-  "node24-file-url-conversion": { run: "SC2020" },
+  "node24-file-url-conversion": { build: "SC1090" },
   "node24-fs-descriptors": { run: "SC1090" },
   "node24-mime": { run: "SC2020" },
   "node24-mime-errors": { run: "SC1090" },
@@ -104,7 +104,7 @@ const KNOWN: Record<string, Known> = {
   "package-imports": { build: "SC2013" },
   "promise-bridge": { build: "SC1090" },
   "self-name": { build: "SC2013" },
-  "stream-shims": { run: "SC1090" },
+  "stream-shims": { build: "SC1090" },
   "util-shims": { run: "SC2020" },
   "web-streams": { run: "SC1090" },
   "workspace-copied": { build: "SC2013" },