FN-5840: harden test project teardown cleanup

Tighten test fixture cleanup so temporary test directories are reliably removed.

- track created test project directories and install process exit/beforeExit backstop cleanup hooks
- make destroyTestProject resilient with async rm plus rmSync fallback and tracked-dir removal
- add regression tests for sqlite wal/shm sibling cleanup and tracked-directory drain behavior
- make db lock-child teardown remove children from tracking during iteration

Files changed:
 packages/core/src/__tests__/db.test.ts           | 10 +++--
 packages/core/src/__tests__/test-project.test.ts | 34 ++++++++++++++-
 packages/core/src/__tests__/test-project.ts      | 54 +++++++++++++++++++++++-
 3 files changed, 92 insertions(+), 6 deletions(-)

Fusion-Task-Id: FN-5840

Fusion-Task-Lineage: 0977be1d-8334-413d-a652-318584d7058b

packages/core/src/__tests__/db.test.ts

@@ -71,14 +71,18 @@ function removeTrackedTmpDirSync(dir: string | undefined): void {
 const activeLockChildren = new Set<ChildProcessWithoutNullStreams>();
 
 function killLockChildrenSync(): void {
-  for (const child of activeLockChildren) {
+  const children = Array.from(activeLockChildren);
+  for (const child of children) {
     try {
-      if (child.exitCode === null && !child.killed) child.kill("SIGKILL");
+      if (child.exitCode === null && !child.killed) {
+        child.kill("SIGKILL");
+      }
     } catch {
       // best-effort
+    } finally {
+      activeLockChildren.delete(child);
     }
   }
-  activeLockChildren.clear();
 }
 
 function cleanupTmpDirsSync(): void {

packages/core/src/__tests__/test-project.test.ts

@@ -1,4 +1,4 @@
-import { mkdtempSync, existsSync, readdirSync } from "node:fs";
+import { mkdtempSync, existsSync, mkdirSync, readdirSync, writeFileSync } from "node:fs";
 import { rm, readFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { isAbsolute, join } from "node:path";
@@ -7,6 +7,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { TaskStore } from "../store.js";
 import {
+  __getTrackedTestProjectDirsForTests,
   createTestProject,
   destroyTestProject,
   seedTasks,
@@ -68,6 +69,22 @@ describe("test-project fixture", () => {
     expect(existsSync(fixture.rootDir)).toBe(false);
   });
 
+  it("destroyTestProject() removes directories containing sqlite wal/shm siblings", async () => {
+    const dir = mkdtempSync(join(tmpdir(), "fusion-test-project-wal-"));
+    extraDirs.add(dir);
+
+    const fusionDir = join(dir, ".fusion");
+    mkdirSync(fusionDir, { recursive: true });
+    writeFileSync(join(fusionDir, "fusion.db"), "db");
+    writeFileSync(join(fusionDir, "fusion.db-wal"), "wal");
+    writeFileSync(join(fusionDir, "fusion.db-shm"), "shm");
+
+    await destroyTestProject(dir);
+
+    extraDirs.delete(dir);
+    expect(existsSync(dir)).toBe(false);
+  });
+
   it(
     "supports multiple isolated projects without cross-interference",
     async () => {
@@ -160,4 +177,19 @@ describe("test-project fixture", () => {
 
     expect(tasks).toHaveLength(4);
   });
+
+  it("cleanup() drains tracked backstop directories", async () => {
+    const fixture = await createFixture();
+    const trackedDirs = __getTrackedTestProjectDirsForTests();
+
+    expect(trackedDirs.has(fixture.rootDir)).toBe(true);
+    expect(trackedDirs.has(fixture.globalDir)).toBe(true);
+
+    await fixture.cleanup();
+
+    expect(trackedDirs.has(fixture.rootDir)).toBe(false);
+    expect(trackedDirs.has(fixture.globalDir)).toBe(false);
+    expect(existsSync(fixture.rootDir)).toBe(false);
+    expect(existsSync(fixture.globalDir)).toBe(false);
+  });
 });

packages/core/src/__tests__/test-project.ts

@@ -1,4 +1,4 @@
-import { mkdtempSync } from "node:fs";
+import { mkdtempSync, rmSync } from "node:fs";
 import { mkdir, rm } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { isAbsolute, join } from "node:path";
@@ -26,6 +26,15 @@ export interface TestProjectFixture {
   cleanup: () => Promise<void>;
 }
 
+const TEST_PROJECT_RM_OPTIONS = {
+  recursive: true,
+  force: true,
+  maxRetries: 5,
+  retryDelay: 50,
+} as const;
+const TRACKED_TEST_PROJECT_DIRS = new Set<string>();
+const TEST_PROJECT_CLEANUP_HOOK_KEY = Symbol.for("fusion.core.test-project.cleanup-hooks-installed");
+
 function assertAbsolutePath(pathValue: string, label: string): void {
   if (!isAbsolute(pathValue)) {
     throw new Error(`${label} must be an absolute path`);
@@ -79,6 +88,11 @@ export async function createTestProject(
   assertAbsolutePath(rootDir, "rootDir");
   assertAbsolutePath(globalDir, "globalSettingsDir");
 
+  TRACKED_TEST_PROJECT_DIRS.add(rootDir);
+  if (ownsGlobalDir) {
+    TRACKED_TEST_PROJECT_DIRS.add(globalDir);
+  }
+
   let store: TaskStore | undefined;
 
   try {
@@ -199,5 +213,41 @@ export async function seedTasks(store: TaskStore, count = 3): Promise<Task[]> {
  */
 export async function destroyTestProject(dir: string): Promise<void> {
   assertAbsolutePath(dir, "dir");
-  await rm(dir, { recursive: true, force: true });
+  try {
+    await rm(dir, TEST_PROJECT_RM_OPTIONS);
+  } catch {
+    try {
+      rmSync(dir, TEST_PROJECT_RM_OPTIONS);
+    } catch {
+      // best-effort fallback during teardown
+    }
+  } finally {
+    TRACKED_TEST_PROJECT_DIRS.delete(dir);
+  }
+}
+
+function cleanupTrackedTestProjectDirsSync(): void {
+  const cleanup = Array.from(TRACKED_TEST_PROJECT_DIRS);
+  for (const dir of cleanup) {
+    try {
+      rmSync(dir, TEST_PROJECT_RM_OPTIONS);
+    } catch {
+      // best-effort fallback during process teardown
+    } finally {
+      TRACKED_TEST_PROJECT_DIRS.delete(dir);
+    }
+  }
+}
+
+const processWithCleanupFlag = process as typeof process & {
+  [TEST_PROJECT_CLEANUP_HOOK_KEY]?: boolean;
+};
+if (!processWithCleanupFlag[TEST_PROJECT_CLEANUP_HOOK_KEY]) {
+  process.once("beforeExit", cleanupTrackedTestProjectDirsSync);
+  process.once("exit", cleanupTrackedTestProjectDirsSync);
+  processWithCleanupFlag[TEST_PROJECT_CLEANUP_HOOK_KEY] = true;
+}
+
+export function __getTrackedTestProjectDirsForTests(): Set<string> {
+  return TRACKED_TEST_PROJECT_DIRS;
 }