fix(observability): avoid mutating captured error names

src/selfhost/sentry.ts

@@ -431,16 +431,21 @@ export async function buildSentryOpenTelemetryBridge(): Promise<OpenTelemetryBri
   };
 }
 
-/** Name a synthetic Error before capture so its Sentry issue title reads "eventName: message" instead of the
+/** Name a captured Error before capture so its Sentry issue title reads "eventName: message" instead of the
  *  generic "Error: message" (or a caught exception's own class name, e.g. "HttpError: ..."). Mirrors
- *  forwardStructuredLogToSentry's `errorEvent.name = event` below — same discipline, applied to the handful of
- *  call sites that construct their OWN `new Error(...)` purely to report a known condition, not to a genuinely
- *  caught exception (which keeps its real name/type — mislabeling those would hide what actually threw). Only
- *  renames when the caller opts in; every other captureError/captureReviewFailure call is unaffected. */
+ *  forwardStructuredLogToSentry's `errorEvent.name = event` below, but never mutates the caught value: some
+ *  runtime errors (notably DOMException from AbortSignal.timeout/fetch) expose a read-only `name` in strict mode. */
 function namedCaptureError(error: unknown, eventName?: string): Error {
   const err = error instanceof Error ? error : new Error(String(error));
-  if (eventName) err.name = eventName;
-  return err;
+  if (!eventName) return err;
+  const namedError = new Error(err.message, { cause: err });
+  namedError.name = eventName;
+  Object.defineProperty(namedError, "stack", {
+    value: err.stack,
+    configurable: true,
+    writable: true,
+  });
+  return namedError;
 }
 
 /** Capture an error with optional structured context. No-op when Sentry is off. `eventName`, when given, becomes

test/unit/selfhost-sentry.test.ts

@@ -621,6 +621,28 @@ describe("enabled when SENTRY_DSN is set", () => {
     expect(lastCapturedError().name).toBe("ai_review_failed");
   });
 
+  it("captureError/captureReviewFailure with an eventName never mutate caught errors that reject name writes", async () => {
+    await initSentry({ SENTRY_DSN: "d" } as unknown as NodeJS.ProcessEnv);
+
+    const timeoutError = new DOMException("signal timed out", "TimeoutError");
+    captureError(timeoutError, { kind: "fetch_timeout" }, "github_fetch_failed");
+
+    expect(timeoutError.name).toBe("TimeoutError");
+    expect(lastCapturedError()).not.toBe(timeoutError);
+    expect(lastCapturedError().name).toBe("github_fetch_failed");
+    expect(lastCapturedError().message).toBe("signal timed out");
+    expect(lastCapturedError().cause).toBe(timeoutError);
+
+    const frozenError = Object.freeze(new Error("review failed"));
+    captureReviewFailure(frozenError, { repo: "o/r" }, "ai_review_failed");
+
+    expect(frozenError.name).toBe("Error");
+    expect(lastCapturedError()).not.toBe(frozenError);
+    expect(lastCapturedError().name).toBe("ai_review_failed");
+    expect(lastCapturedError().message).toBe("review failed");
+    expect(lastCapturedError().cause).toBe(frozenError);
+  });
+
   it("adds active OTEL trace ids to captured Sentry events", async () => {
     await initSentry({ SENTRY_DSN: "d" } as unknown as NodeJS.ProcessEnv);
     otelMocks.currentOtelTraceIds.mockReturnValue({