diff --git a/packages/coding-agent/src/tools/browser/cmux/cmux-tab.ts b/packages/coding-agent/src/tools/browser/cmux/cmux-tab.ts
index 85e5e3619..f307cae69 100644
--- a/packages/coding-agent/src/tools/browser/cmux/cmux-tab.ts
+++ b/packages/coding-agent/src/tools/browser/cmux/cmux-tab.ts
@@ -10,7 +10,7 @@ import { resolveToCwd } from "../../path-utils";
 import { formatScreenshot } from "../../render-utils";
 import {
 	bindRunFacade,
-	isBrowserRunRejection,
+	isBrowserRunOwnedRejection,
 	markBrowserRunRejection,
 	observeBrowserRunPromise,
 	resolvePredicateTimeout,
@@ -1409,9 +1409,7 @@ export async function runCmuxCode(tab: CmuxTab, opts: RunCmuxCodeOptions): Promi
 		rejectFloatingFailure(error);
 	};
 	const uninstallRejectionInterceptor = postmortem.interceptUnhandledRejections(reason => {
-		const browserRunRejection = isBrowserRunRejection(reason, rejectionOwner);
-		const stack = reason instanceof Error && typeof reason.stack === "string" ? reason.stack : undefined;
-		if (!browserRunRejection && stack?.includes(`cmux-run-${runId}.js`) !== true) return false;
+		if (!isBrowserRunOwnedRejection(reason, rejectionOwner, `cmux-run-${runId}.js`)) return false;
 		recordFloatingFailure(reason);
 		return true;
 	});
diff --git a/packages/coding-agent/src/tools/browser/tab-worker.ts b/packages/coding-agent/src/tools/browser/tab-worker.ts
index cd50e8795..f8d442afe 100644
--- a/packages/coding-agent/src/tools/browser/tab-worker.ts
+++ b/packages/coding-agent/src/tools/browser/tab-worker.ts
@@ -24,7 +24,7 @@ import {
 	bindRunFacade,
 	CELL_BUDGET_SLACK_MS,
 	installBrowserWorkerRejectionGuard,
-	isBrowserRunRejection,
+	isBrowserRunOwnedRejection,
 	markBrowserRunRejection,
 	markHandled,
 	observeBrowserRunPromise,
@@ -784,10 +784,7 @@ export class WorkerCore {
 	#consumeUnhandledRejection(reason: unknown): boolean {
 		const active = this.#active;
 		if (!active) return false;
-		const browserRunRejection = isBrowserRunRejection(reason, active.rejectionOwner);
-		const stack = reason instanceof Error && typeof reason.stack === "string" ? reason.stack : undefined;
-		const fromRun = stack?.includes(`browser-run-${active.id}.js`) === true;
-		if (!browserRunRejection && !this.#isolated && !fromRun) return false;
+		if (!isBrowserRunOwnedRejection(reason, active.rejectionOwner, `browser-run-${active.id}.js`)) return false;
 		this.#recordFloatingRejection(active, reason);
 		return true;
 	}
diff --git a/packages/coding-agent/src/tools/run-scope.ts b/packages/coding-agent/src/tools/run-scope.ts
index f519565c8..db83e1bc7 100644
--- a/packages/coding-agent/src/tools/run-scope.ts
+++ b/packages/coding-agent/src/tools/run-scope.ts
@@ -22,6 +22,12 @@ export function isBrowserRunRejection(reason: unknown, owner: object): boolean {
 	);
 }
 
+/** Returns whether a rejection belongs to the marked browser run or its evaluated source file. */
+export function isBrowserRunOwnedRejection(reason: unknown, owner: object, filename: string): boolean {
+	if (isBrowserRunRejection(reason, owner)) return true;
+	return reason instanceof Error && typeof reason.stack === "string" && reason.stack.includes(filename);
+}
+
 type FloatingRejectionHandler = (reason: unknown) => void;
 
 interface ObservedPromiseState {
diff --git a/packages/coding-agent/test/tools/browser-run-cancellation.test.ts b/packages/coding-agent/test/tools/browser-run-cancellation.test.ts
index 5c85bf566..133a7bdd9 100644
--- a/packages/coding-agent/test/tools/browser-run-cancellation.test.ts
+++ b/packages/coding-agent/test/tools/browser-run-cancellation.test.ts
@@ -4,6 +4,7 @@ import { postmortem } from "@oh-my-pi/pi-utils";
 import { JsRuntime, type RuntimeHooks } from "../../src/eval/js/shared/runtime";
 import {
 	bindRunFacade,
+	isBrowserRunOwnedRejection,
 	isBrowserRunRejection,
 	markBrowserRunRejection,
 	markHandled,
@@ -147,6 +148,20 @@ describe("browser run cancellation", () => {
 		expect(isBrowserRunRejection(new Error("unrelated", { cause: browserFailure }), owner)).toBe(false);
 	});
 
+	it("keeps unrelated worker rejections outside the active browser run", () => {
+		const owner = {};
+		const workerFailure = new Error("transport failed");
+		workerFailure.stack = "Error: transport failed\n    at tab-worker.ts:1:1";
+		const evaluatedFailure = new Error("evaluated failure");
+		evaluatedFailure.stack = "Error: evaluated failure\n    at browser-run-run-1.js:1:1";
+
+		expect(isBrowserRunOwnedRejection(workerFailure, owner, "browser-run-run-1.js")).toBe(false);
+		expect(isBrowserRunOwnedRejection(evaluatedFailure, owner, "browser-run-run-1.js")).toBe(true);
+		expect(
+			isBrowserRunOwnedRejection(markBrowserRunRejection(workerFailure, owner), owner, "browser-run-run-1.js"),
+		).toBe(true);
+	});
+
 	it("keeps a later cause-wrapped rejection on the fatal path", async () => {
 		vi.useRealTimers();
 		const script = `