test: harden threaded channel follow-ups

src/infra/file-lock.ts

@@ -1,6 +1,7 @@
 export type { FileLockHandle, FileLockOptions } from "../plugin-sdk/file-lock.js";
 export {
   acquireFileLock,
+  drainFileLockStateForTest,
   resetFileLockStateForTest,
   withFileLock,
 } from "../plugin-sdk/file-lock.js";

src/plugin-sdk/file-lock.ts

@@ -40,6 +40,14 @@ function releaseAllLocksSync(): void {
   }
 }
 
+async function drainAllLocks(): Promise<void> {
+  for (const [normalizedFile, held] of Array.from(HELD_LOCKS.entries())) {
+    HELD_LOCKS.delete(normalizedFile);
+    await held.handle.close().catch(() => undefined);
+    await fs.rm(held.lockPath, { force: true }).catch(() => undefined);
+  }
+}
+
 function rmLockPathSync(lockPath: string): void {
   try {
     fsSync.rmSync(lockPath, { force: true });
@@ -133,6 +141,10 @@ export function resetFileLockStateForTest(): void {
   releaseAllLocksSync();
 }
 
+export async function drainFileLockStateForTest(): Promise<void> {
+  await drainAllLocks();
+}
+
 /** Acquire a re-entrant process-local file lock backed by a `.lock` sidecar file. */
 export async function acquireFileLock(
   filePath: string,

src/test-utils/session-state-cleanup.ts

@@ -1,7 +1,9 @@
 import { drainSessionWriteLockStateForTest } from "../agents/session-write-lock.js";
 import { clearSessionStoreCacheForTest } from "../config/sessions/store.js";
+import { drainFileLockStateForTest } from "../infra/file-lock.js";
 
 export async function cleanupSessionStateForTest(): Promise<void> {
   clearSessionStoreCacheForTest();
+  await drainFileLockStateForTest();
   await drainSessionWriteLockStateForTest();
 }