@@ -54,6 +54,20 @@ test('publication is atomic, binds identity and paths, and excludes a second acq
   assert.deepEqual(readDaemonShutdownReport(paths.baseDir), report);
 });
 
+test('publication truncates the log the daemon is already appending to', async () => {
+  const { paths, owner } = await acquire();
+  const daemonOutput = fs.openSync(paths.logPath, 'a');
+  try {
+    fs.writeSync(daemonOutput, 'previous run\n');
+    owner.publish(fields);
+    fs.writeSync(daemonOutput, 'listening\n');
+  } finally {
+    fs.closeSync(daemonOutput);
+  }
+  assert.equal(fs.readFileSync(paths.logPath, 'utf8'), 'listening\n');
+  await owner.finish(report);
+});
+
 for (const [pid, startTime, reason] of [
   [999_999_999, 'successor-start', 'replaced'],
   [process.pid, 'recycled-start', 'replaced'],
 
@@ -64,7 +64,7 @@ export async function tryAcquireDaemonRegistration(
     owner: Object.freeze({
       publish({ socketPort, httpPort, ...fields }: DaemonRegistrationFields) {
         acquisition.assertHeld();
-        publishFileSync({ destination: boundPaths.logPath, contents: '', mode: 0o600 });
+        truncateDaemonLog(boundPaths.logPath);
         const transport = socketPort && httpPort ? 'dual' : httpPort ? 'http' : 'socket';
         acquisition.assertHeld();
         publishFileSync({
@@ -153,3 +153,13 @@ function writeShutdownReport(
     return;
   }
 }
+
+/** The daemon's stdout and stderr append to this inode, so it is emptied in place, never replaced. */
+function truncateDaemonLog(logPath: string): void {
+  const descriptor = fs.openSync(logPath, 'a', 0o600);
+  try {
+    fs.ftruncateSync(descriptor, 0);
+  } finally {
+    fs.closeSync(descriptor);
+  }
+}
@@ -6,6 +6,11 @@ import { setActiveProviderDeviceRuntimes } from '../../provider-device-runtime.t
 import { IOS_SIMULATOR } from '../../__tests__/test-utils/device-fixtures.ts';
 import { mkdtempForTestSync } from '../../__tests__/test-utils/tmp-dir.ts';
 import { createDaemonProviderRuntimeComposition } from '../../provider-device-runtimes.ts';
+import {
+  DAEMON_STARTUP_EXIT_CODES,
+  tryAcquireDaemonRegistration,
+} from '../../daemon-registration-owner.ts';
+import { resolveDaemonPaths } from '../../daemon-resolution.ts';
 import { interactorResolution } from '../interactor-resolution.ts';
 
 vi.mock('../../platform-runtime.ts', () => ({
@@ -85,7 +90,9 @@ test('daemon startup composes the interactor resolution the daemon resolves thro
 });
 
 test('a daemon attempt losing the lock shuts down every constructed provider', async () => {
-  vi.spyOn(await import('./server-lifecycle.ts'), 'acquireDaemonLock').mockReturnValueOnce(false);
+  const stateDir = mkdtempForTestSync('daemon-held-lock-');
+  const held = await tryAcquireDaemonRegistration(resolveDaemonPaths(stateDir));
+  if (held.status !== 'acquired') throw new Error('registration fixture refused');
   const shutdown = vi.fn(() => {
     throw new Error('cleanup failed');
   });
@@ -103,7 +110,7 @@ test('a daemon attempt losing the lock shuts down every constructed provider', a
   });
   const exit = vi.fn();
   const runtime = await startDaemonRuntime({
-    env: { AGENT_DEVICE_STATE_DIR: mkdtempForTestSync('daemon-held-lock-') },
+    env: { AGENT_DEVICE_STATE_DIR: stateDir },
     exit,
     registerProcessHandlers: false,
     stderr: { write: () => {} },
@@ -112,5 +119,6 @@ test('a daemon attempt losing the lock shuts down every constructed provider', a
   expect(runtime).toBeNull();
   expect(shutdown).toHaveBeenCalledOnce();
   expect(otherShutdown).toHaveBeenCalledOnce();
-  expect(exit).toHaveBeenCalledWith(0);
+  expect(exit).toHaveBeenCalledWith(DAEMON_STARTUP_EXIT_CODES.busy);
+  await held.owner.finish();
 });