@@ -82,6 +82,25 @@ extension RunnerTests {
     RunnerSnapshotBridgeDrainForTest()
     let admitted = RunnerSnapshotBridgeReadForTest(request, 1000, { ["ok": true] }, 16)
     XCTAssertEqual(admitted["ok"] as? Bool, true)
+
+    let started = DispatchSemaphore(value: 0)
+    let secondRelease = DispatchSemaphore(value: 0)
+    let finished = expectation(description: "second read outlives its budget")
+    DispatchQueue.global().async {
+      let second = RunnerSnapshotBridgeReadForTest(request, 1000, {
+        started.signal()
+        secondRelease.wait()
+        return ["ok": true]
+      }, 100)
+      XCTAssertEqual(second["error_code"] as? String, "bridge-read-abandoned")
+      finished.fulfill()
+    }
+    started.wait()
+    let secondBusy = RunnerSnapshotBridgeReadForTest(request, 100, { ["ok": true] }, 100)
+    XCTAssertEqual(secondBusy["error_code"] as? String, "bridge-read-in-flight")
+    wait(for: [finished], timeout: 5)
+    secondRelease.signal()
+    RunnerSnapshotBridgeDrainForTest()
   }
 
   func testReaderDoesNotRefuseTheBoundsOfAFirstRead() throws {
 
@@ -335,7 +335,7 @@ async function heartbeatLease(
         phase: 'lease_provider_ended_session_teardown_failed',
         data: {
           leaseId: lease.leaseId,
-          error: error instanceof Error ? error.message : String(error),
+          error: errorMessage(error),
         },
       });
     }
 
@@ -39,13 +39,15 @@ type RunnerProcess = { pid: number; processStartTime: string };
  * foreground process, and `describe` reads it unless the host planned another process, or answers
  * the refusal `refuseDescribe` names. A describe given `holdNextDescribe` reads until that promise
  * settles, and, like the runner, it keeps reading after the daemon stops waiting: a describe that
- * arrives meanwhile is refused as `bridge-read-in-flight`. A describe that names surface hosts is
- * refused as `system-surface-host-unverified`, as a sandbox that refuses the process table does.
+ * arrives meanwhile is refused as `bridge-read-in-flight`. With `refuseSurfaceHostCheck`, a describe that
+ * names surface hosts is refused as `system-surface-host-unverified`, as a sandbox that refuses the
+ * process table does.
  */
 function bridgeRunner(state: {
   process: RunnerProcess;
   refuseDescribe?: string;
   refuseTarget?: string;
+  refuseSurfaceHostCheck?: boolean;
   holdNextDescribe?: Promise<void>;
 }) {
   const sent: RunnerCommand[] = [];
@@ -86,7 +88,7 @@ function bridgeRunner(state: {
       ) {
         return refusal('stale_target', 'target-process-changed');
       }
-      if (request.surfaceHostExecutables)
+      if (request.surfaceHostExecutables && state.refuseSurfaceHostCheck)
         return refusal('unsupported', 'system-surface-host-unverified');
       if (state.refuseDescribe) return refusal('application_not_responding', state.refuseDescribe);
       if (reading) return refusal('application_not_responding', 'bridge-read-in-flight');
@@ -142,7 +144,7 @@ function verbs(sent: readonly RunnerCommand[]): string[] {
   return sent.map((command) => command.snapshotBridge?.verb ?? command.command);
 }
 
-/** The bridge route of a runner whose foreground read proves no system surface covers the app. */
+/** The bridge route of a runner with an optional foreground session. */
 function bridgeRoute(provider: AppleRunnerProvider, runnerSessionId?: string) {
   const bridge = createRunnerSnapshotBridge({ device: IOS_SIMULATOR, provider });
   const presented: SnapshotRuntimeAcquiredResult[] = [];
@@ -165,7 +167,9 @@ function bridgeRoute(provider: AppleRunnerProvider, runnerSessionId?: string) {
       ...(runnerSessionId ? { sessionChanged: bridge.resetTargets } : {}),
     },
     async () =>
-      runnerSessionId ? { foreground: 'background', sessionId: runnerSessionId } : 'background',
+      runnerSessionId
+        ? { foreground: 'background', sessionId: runnerSessionId }
+        : { foreground: 'unknown' },
   );
   const snapshot = (signal = new AbortController().signal) =>
     route.capture(
@@ -427,6 +431,7 @@ test('the runner runtime reads a remote Simulator through the bridge once its fo
 
 test('a runner whose foreground read cannot answer asks the bridge read to check the surface hosts', async () => {
   const { provider, sent } = bridgeRunner({
+    refuseSurfaceHostCheck: true,
     process: { pid: 41, processStartTime: '1700000000.000001' },
   });
   const { snapshot, fallbacks } = runtimeSnapshots(withHostStates(provider, undefined));
@@ -478,6 +483,7 @@ test('the foreground proof starts the runner when none is live, then reads only
 test('a runner whose session id cannot be read answers the foreground proof as unknown', async () => {
   registry.session = undefined;
   const { provider, sent } = bridgeRunner({
+    refuseSurfaceHostCheck: true,
     process: { pid: 41, processStartTime: '1700000000.000001' },
   });
   const { snapshot, fallbacks } = runtimeSnapshots(withHostStates(provider, 'notRunning'));
@@ -650,7 +656,7 @@ test('a wedge before the runner id is known does not disable a newly identified
       targetFreshness: 'cached',
       sessionChanged: bridge.resetTargets,
     },
-    async () => (sessionId ? { foreground: 'background', sessionId } : 'background'),
+    async () => (sessionId ? { foreground: 'background', sessionId } : { foreground: 'unknown' }),
   );
   const snapshot = () =>
     route.capture(
 
@@ -132,11 +132,12 @@ test.for([
   async ({ runner, host, acquired, checked, served }) => {
     const source = sourceReturning(host === 'present' ? surfaceHostPresent : bridgeAcquisition());
     const fallback = vi.fn(async () => runnerResult());
-    const systemSurfaceForeground = vi.fn(async () =>
-      runner === 'foreground'
-        ? ({ kind: 'foreground', host: presentSurface.host } as const)
-        : runner,
-    );
+    const systemSurfaceForeground = vi.fn(async () => ({
+      foreground:
+        runner === 'foreground'
+          ? ({ kind: 'foreground', host: presentSurface.host } as const)
+          : runner,
+    }));
     const route = createAppleSnapshotRoute(bridgePresentingHost(), {
       source,
       resolveTarget: vi.fn(async () => target),
 
@@ -211,10 +211,7 @@ function createSnapshotBridgeRouteCore<Target extends SnapshotBridgeRouteTarget>
     probeResult: Awaited<ReturnType<SystemSurfaceForegroundProbe>>,
     device: DeviceInfo,
   ): typeof currentCircuit => {
-    const probedSessionId =
-      channel.sessionChanged && typeof probeResult === 'object' && 'sessionId' in probeResult
-        ? probeResult.sessionId
-        : undefined;
+    const probedSessionId = channel.sessionChanged ? probeResult.sessionId : undefined;
     if (probedSessionId === undefined) return startingCircuit;
     if (currentCircuit !== startingCircuit) {
       return probedSessionId === currentCircuit.sessionId ? currentCircuit : startingCircuit;
@@ -264,10 +261,7 @@ function createSnapshotBridgeRouteCore<Target extends SnapshotBridgeRouteTarget>
       const startingCircuit = currentCircuit;
       const probeResult = await readSurfaceForeground(device, input, signal, surfaceForeground);
       const circuit = circuitForProbe(startingCircuit, probeResult, device);
-      const foreground =
-        typeof probeResult === 'object' && 'sessionId' in probeResult
-          ? probeResult.foreground
-          : probeResult;
+      const { foreground } = probeResult;
       const captureBridgeDisabled = (target: SnapshotBridgeRouteTarget) =>
         isDisabledIn(circuit, target);
       if (foreground !== 'background' && foreground !== 'unknown') {
@@ -460,12 +454,7 @@ async function readSurfaceForeground(
 ): Promise<Awaited<ReturnType<SystemSurfaceForegroundProbe>>> {
   const requestId = input.execution?.requestId;
   const foreground = await probe(device, { signal, ...(requestId ? { requestId } : {}) });
-  if (
-    foreground === 'background' ||
-    (typeof foreground === 'object' &&
-      'sessionId' in foreground &&
-      foreground.foreground === 'background')
-  ) {
+  if (foreground.foreground === 'background') {
     emitDiagnostic({
       level: 'debug',
       phase: 'ios_snapshot_route_surface_host_background',
 
@@ -96,7 +96,7 @@ test.for([
 ] as const)('%s is unknown and sends no command', async ([, liveness]) => {
   runner.readRunnerSessionLiveness.mockReturnValue(liveness);
 
-  await expect(probe()).resolves.toBe('unknown');
+  await expect(probe()).resolves.toEqual({ foreground: 'unknown' });
   expect(runner.runAppleRunnerCommand).not.toHaveBeenCalled();
 });
 
 
@@ -26,9 +26,7 @@ export type SystemSurfaceForeground =
 export type SystemSurfaceForegroundProbe = (
   device: DeviceInfo,
   input: Readonly<{ signal: AbortSignal; requestId?: string }>,
-) => Promise<
-  SystemSurfaceForeground | Readonly<{ foreground: SystemSurfaceForeground; sessionId: string }>
->;
+) => Promise<Readonly<{ foreground: SystemSurfaceForeground; sessionId?: string }>>;
 
 /**
  * Bounds each read below the read-only resend window, so a runner busy draining abandoned XCTest
@@ -65,7 +63,7 @@ export function createSystemSurfaceForegroundProbe(
 ): SystemSurfaceForegroundProbe {
   return async (device, input) => {
     const session = await readySession(device, input);
-    if (!session) return 'unknown';
+    if (!session) return { foreground: 'unknown' };
     // The reads go out together: each one is a runner round trip, which costs a network hop to a
     // remote Simulator. The answer reads them in registry order, so a decisive state settles it
     // without waiting for the hosts after it.
Original file line number	Diff line number	Diff line change
`@@ -335,7 +335,7 @@ async function heartbeatLease(`
`335`	`335`	`phase: 'lease_provider_ended_session_teardown_failed',`
`336`	`336`	`data: {`
`337`	`337`	`leaseId: lease.leaseId,`
`338`		`- error: error instanceof Error ? error.message : String(error),`
	`338`	`+ error: errorMessage(error),`
`339`	`339`	`},`
`340`	`340`	`});`
`341`	`341`	`}`