perf(fast-browser): compute scoped origin policy without worker dispatch

extensions/fast-browser/runtime.ts

@@ -449,6 +449,30 @@ export function createBrowserRuntime(
     return run;
   };
 
+  // Policy narrowing is a runtime concern, not a worker operation. Keep it
+  // on the same lane so it observes the same lifecycle and serialization
+  // boundaries without starting a transport or emitting JSONL.
+  const invokeLocal = <T>(
+    operation: BrowserRuntimeOperationName,
+    signal: AbortSignal,
+    action: () => T,
+  ): Promise<T> => {
+    const run = lane.then(() => {
+      if (closed && operation !== "close") throw operationError(operation, "lifecycle", "browser_closed", "browser session is closed", "not_attempted");
+      if (parentSignal.aborted && operation !== "close") throw operationError(operation, "lifecycle", "browser_closed", "browser session is unavailable", "not_attempted");
+      // Match invoke(): a pre-aborted operation signal is rejected before
+      // dispatch/error shaping, while lifecycle failures remain typed.
+      throwIfAborted(signal);
+      try {
+        return action();
+      } catch (error) {
+        throw asOperationError(error, operation, "dispatch", false);
+      }
+    });
+    lane = run.catch(() => undefined);
+    return run;
+  };
+
   const captureAfterFailure = async (operation: BrowserRuntimeOperationName, context?: RuntimeOperationContext): Promise<FailureCaptureSummary> => {
     if (parentSignal.aborted) return { status: "unavailable", reason: "browser session is unavailable" };
     if (operation === "captureEvidence" || operation === "close" || operation === "narrowOriginPolicy") {
@@ -500,6 +524,10 @@ export function createBrowserRuntime(
       const controller = new AbortController();
       const timed = timedSignal(controller.signal, OPERATION_BUDGETS.close);
       try {
+        // Wait for local-only operations too. A narrow policy must not race
+        // session teardown, and waiting here still keeps an unused transport
+        // unstarted.
+        await lane;
         if (transport) {
           await invoke("close", { op: "close" }, timed.signal, undefined, () => undefined).catch(() => undefined);
           await transport.close().catch(() => {});
@@ -612,11 +640,7 @@ export function createBrowserRuntime(
       const allowedOrigins = normalizePolicy(request.allowedOrigins);
       if (basePolicy !== "*" && (allowedOrigins === "*" || allowedOrigins.some((origin) => !basePolicy.includes(origin)))) throw operationError("narrowOriginPolicy", "policy", "policy_denied", "origin policy cannot be broadened", "not_attempted");
       const context = { allowedOrigins };
-      const result = await invoke("narrowOriginPolicy", { op: "narrowOriginPolicy", request: { allowedOrigins } }, signal, { allowedOrigins: basePolicy }, (raw) => {
-        if (!raw || typeof raw !== "object" || !("allowedOrigins" in raw)) throw new Error("worker returned invalid origin policy");
-        return context;
-      });
-      return result;
+      return invokeLocal("narrowOriginPolicy", signal, () => context);
     },
     close,
   };