diff --git a/packages/compiler/src/frontend/lowering/lowerer.ts b/packages/compiler/src/frontend/lowering/lowerer.ts
index 94d526831..e19c4785d 100644
--- a/packages/compiler/src/frontend/lowering/lowerer.ts
+++ b/packages/compiler/src/frontend/lowering/lowerer.ts
@@ -9872,27 +9872,21 @@ 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/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/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/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/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/corpus-costs.json b/tests/harness/corpus-costs.json
index e211a263b..b91073f87 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,
@@ -5247,7 +5246,6 @@
     "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/npm.test.ts b/tests/harness/npm.test.ts
index c4e70294e..a6cdee2b5 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": { build: "SC2013" },
   "workspace-copied": { build: "SC2013" },