feat(FN-3827): sweep stale autostashes after merge completion

Merger now properly cleans up autostash git refs that survive past their useful lifetime, fixing race conditions during restore/cleanup and adding scheduled stale-sweep runs in the engine. The feature includes docs for the autostash lifecycle, new test coverage for the cleanup and sweep paths, and a

Fusion-Task-Id: FN-3827

packages/engine/src/__tests__/merger-autostash-cleanup.test.ts

@@ -6,7 +6,7 @@ import { execSync } from "node:child_process";
 import type { TaskStore } from "@fusion/core";
 import { __test__ } from "../merger.js";
 
-const { sweepAutostashOrphans, parseAutostashTaskId } = __test__;
+const { sweepAutostashOrphans, parseAutostashTaskId, sweepStaleAutostashes, dropAutostashHandle } = __test__;
 
 function git(cwd: string, cmd: string): string {
   return execSync(cmd, { cwd, stdio: "pipe" }).toString("utf-8").trim();
@@ -65,6 +65,82 @@ describe("parseAutostashTaskId", () => {
   });
 });
 
+describe("sweepStaleAutostashes", () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), "fn-autostash-stale-"));
+    initRepo(dir);
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it("drops stale autostashes older than maxAgeMs", async () => {
+    const oldTs = Date.now() - 26 * 60 * 60 * 1000;
+    const staleLabel = `fusion-merger-autostash:FN-5001:${oldTs}`;
+    writeFileSync(join(dir, "file.txt"), "stale\n");
+    git(dir, `git stash push -m ${JSON.stringify(staleLabel)} file.txt`);
+
+    const res = await sweepStaleAutostashes(dir, { maxAgeMs: 24 * 60 * 60 * 1000 });
+
+    expect(res.dropped).toBe(1);
+    expect(stashList(dir)).not.toContain("fusion-merger-autostash:FN-5001");
+  });
+
+  it("keeps recent autostashes within maxAgeMs", async () => {
+    const freshLabel = `fusion-merger-autostash:FN-5002:${Date.now()}`;
+    writeFileSync(join(dir, "file.txt"), "fresh\n");
+    git(dir, `git stash push -m ${JSON.stringify(freshLabel)} file.txt`);
+
+    const res = await sweepStaleAutostashes(dir, { maxAgeMs: 24 * 60 * 60 * 1000 });
+
+    expect(res.dropped).toBe(0);
+    expect(stashList(dir)).toContain("fusion-merger-autostash:FN-5002");
+  });
+
+  it("ignores non-fusion stash labels", async () => {
+    writeFileSync(join(dir, "file.txt"), "manual\n");
+    git(dir, "git stash push -m \"manual\" file.txt");
+
+    const res = await sweepStaleAutostashes(dir, { maxAgeMs: 1 });
+
+    expect(res.dropped).toBe(0);
+    expect(stashList(dir)).toContain("manual");
+  });
+
+  it("tolerates malformed autostash labels", async () => {
+    const malformed = "fusion-merger-autostash:FN-5003:not-a-timestamp";
+    writeFileSync(join(dir, "file.txt"), "bad\n");
+    git(dir, `git stash push -m ${JSON.stringify(malformed)} file.txt`);
+
+    await expect(sweepStaleAutostashes(dir, { maxAgeMs: 1 })).resolves.toEqual({ dropped: 0 });
+    expect(stashList(dir)).toContain("not-a-timestamp");
+  });
+
+  it("dropAutostashHandle drops primary and rescue shas", async () => {
+    const pLabel = `fusion-merger-autostash:FN-5004:${Date.now() - 1000}`;
+    writeFileSync(join(dir, "file.txt"), "primary\n");
+    git(dir, `git stash push -m ${JSON.stringify(pLabel)} file.txt`);
+    const primarySha = git(dir, 'git stash list --format="%H" -n 1');
+
+    const rLabel = `fusion-merger-autostash:FN-5004:race-rescue-0:${Date.now() - 500}`;
+    writeFileSync(join(dir, "file.txt"), "rescue\n");
+    git(dir, `git stash push -m ${JSON.stringify(rLabel)} file.txt`);
+    const rescueSha = git(dir, 'git stash list --format="%H" -n 1');
+
+    const result = await dropAutostashHandle(dir, "FN-5004", {
+      sha: primarySha,
+      label: pLabel,
+      rescueShas: [{ sha: rescueSha, label: rLabel }],
+    }, { keepIfLive: false });
+
+    expect(result.dropped).toBe(2);
+    expect(stashList(dir)).toBe("");
+  });
+});
+
 describe("sweepAutostashOrphans", () => {
   let dir: string;
 

packages/engine/src/__tests__/merger.test.ts

@@ -486,6 +486,61 @@ describe("aiMergeTask abort handling", () => {
   });
 });
 
+describe("aiMergeTask autostash cleanup", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockedExistsSync.mockReturnValue(true);
+    mockedCreateFnAgent.mockResolvedValue({
+      session: {
+        prompt: vi.fn().mockResolvedValue(undefined),
+        dispose: vi.fn(),
+      },
+    } as any);
+  });
+
+  it("drops task autostash after successful merge restore", async () => {
+    const store = createMockStore({ id: "FN-050", worktree: "/tmp/root/.worktrees/KB-050" });
+    const stashSha = "1111111111111111111111111111111111111111";
+    let dropped = false;
+
+    mockedExecSync.mockImplementation((cmd: any) => {
+      const cmdStr = String(cmd);
+      if (cmdStr.includes('git stash list --format="%H %gd %s"')) {
+        return dropped ? "" : `${stashSha} stash@{0} fusion-merger-autostash:FN-050:1`;
+      }
+      if (cmdStr.includes("git status -z --porcelain")) return " M file.txt\0" as any;
+      if (cmdStr.includes("git stash create")) return stashSha as any;
+      if (cmdStr.includes("git stash store")) return "" as any;
+      if (cmdStr.includes('git stash list --format="%H %gd"')) return dropped ? "" : `${stashSha} stash@{0}`;
+      if (cmdStr.includes("git rev-parse stash@{0}")) return stashSha as any;
+      if (cmdStr.includes("git stash drop stash@{0}")) {
+        dropped = true;
+        return "" as any;
+      }
+      if (cmdStr.includes("git stash apply")) return "" as any;
+      if (cmdStr.includes("rev-parse --verify")) return Buffer.from("abc123");
+      if (cmdStr === "git rev-parse HEAD" || cmdStr.startsWith("git rev-parse HEAD ")) return "mergedcommit123";
+      if (cmdStr.includes("git log")) return "- feat: something" as any;
+      if (cmdStr.includes("merge-base")) return Buffer.from("abc123");
+      if (cmdStr.includes("git diff") && cmdStr.includes("--stat")) return "1 file changed" as any;
+      if (cmdStr.includes("merge --squash")) return Buffer.from("");
+      if (cmdStr.includes("diff --cached --quiet")) return "1" as any;
+      if (cmdStr.includes("diff --cached")) return "0" as any;
+      if (cmdStr.includes("show --shortstat")) return "3 files changed, 10 insertions(+), 2 deletions(-)" as any;
+      if (cmdStr.includes("branch -d") || cmdStr.includes("branch -D")) return Buffer.from("");
+      if (cmdStr.includes("worktree remove")) return Buffer.from("");
+      return Buffer.from("");
+    });
+
+    await aiMergeTask(store, "/tmp/root", "FN-050");
+
+    expect(dropped).toBe(true);
+    expect(
+      mockedExecSync.mock.calls.some((call) => String(call[0]).includes("git stash drop stash@{0}")),
+    ).toBe(true);
+  });
+});
+
 describe("aiMergeTask — conditional worktree cleanup", () => {
   beforeEach(() => {
     vi.clearAllMocks();

packages/engine/src/merger.ts

@@ -1448,9 +1448,46 @@ async function sweepAutostashOrphans(
   }
 }
 
+const AUTOSTASH_TIMESTAMP_RE = /^fusion-merger-autostash:[A-Za-z]+-\d+:(?:race-rescue-\d+:)?(\d+)$/;
+
+export async function sweepStaleAutostashes(
+  rootDir: string,
+  options: { maxAgeMs: number; taskStore?: TaskStore },
+): Promise<{ dropped: number }> {
+  try {
+    void options.taskStore;
+    const now = Date.now();
+    const threshold = Math.max(0, Math.trunc(options.maxAgeMs));
+    const entries = await listOrphanedAutostashes(rootDir);
+    let dropped = 0;
+
+    for (const entry of entries) {
+      const match = AUTOSTASH_TIMESTAMP_RE.exec(entry.label.trim());
+      if (!match) continue;
+      const ts = Number.parseInt(match[1] ?? "", 10);
+      if (!Number.isFinite(ts)) continue;
+      if (now - ts <= threshold) continue;
+      const sourceTaskId = parseAutostashTaskId(entry.label) ?? "autostash-sweep";
+      const result = await dropAutostashBySha(rootDir, sourceTaskId, entry.sha);
+      if (result.dropped) dropped += 1;
+    }
+
+    const hours = Math.max(1, Math.round(threshold / 3_600_000));
+    mergerLog.log(`startup-sweep: dropped ${dropped} stale fusion-merger-autostash entries older than ${hours}h`);
+    return { dropped };
+  } catch (err: unknown) {
+    const msg = err instanceof Error ? err.message : String(err);
+    mergerLog.warn(`startup-sweep: stale autostash sweep failed (${msg})`);
+    return { dropped: 0 };
+  }
+}
+
 export const __test__ = {
   sweepAutostashOrphans,
   parseAutostashTaskId,
+  dropAutostashHandle,
+  isAutostashLive,
+  sweepStaleAutostashes,
 };
 
 async function stashUnrelatedRootDirChanges(
@@ -1652,6 +1689,73 @@ async function dropAutostashBySha(
   return { dropped: false, reason: "exhausted retry attempts" };
 }
 
+async function isAutostashLive(rootDir: string, sha: string): Promise<boolean> {
+  try {
+    const stashFiles = await listStashChangedPaths(rootDir, sha);
+    if (stashFiles.size === 0) return false;
+    const pathsArg = [...stashFiles].map(quoteArg).join(" ");
+    const { stdout: pathDiffOut } = await execAsync(
+      `git diff --name-only HEAD ${quoteArg(sha)} -- ${pathsArg}`,
+      { cwd: rootDir, encoding: "utf-8" },
+    );
+    return pathDiffOut.trim().length > 0;
+  } catch {
+    return true;
+  }
+}
+
+async function dropAutostashHandle(
+  rootDir: string,
+  taskId: string,
+  handle: AutostashHandle,
+  options: {
+    keepIfLive: boolean;
+    store?: TaskStore;
+    context?: string;
+  },
+): Promise<{ dropped: number; keptLive: number; failed: number }> {
+  const entries = [
+    { sha: handle.sha, label: handle.label, kind: "primary" as const },
+    ...(handle.rescueShas ?? []).map((r) => ({ sha: r.sha, label: r.label, kind: "race-rescue" as const })),
+  ];
+
+  let dropped = 0;
+  let keptLive = 0;
+  let failed = 0;
+
+  for (const entry of entries) {
+    if (options.keepIfLive) {
+      const live = await isAutostashLive(rootDir, entry.sha);
+      if (live) {
+        keptLive += 1;
+        mergerLog.warn(`${taskId}: preserving live ${entry.kind} autostash ${entry.sha.slice(0, 7)} (${entry.label})`);
+        continue;
+      }
+    }
+
+    const dropResult = await dropAutostashBySha(rootDir, taskId, entry.sha);
+    if (dropResult.dropped) {
+      dropped += 1;
+      mergerLog.log(`${taskId}: dropped ${entry.kind} autostash ${entry.sha.slice(0, 7)} (${entry.label})`);
+    } else {
+      failed += 1;
+      mergerLog.warn(
+        `${taskId}: failed to drop ${entry.kind} autostash ${entry.sha.slice(0, 7)} (${entry.label}) — ${dropResult.reason ?? "unknown"}`,
+      );
+    }
+  }
+
+  if (options.store && options.context) {
+    await options.store.logEntry(
+      taskId,
+      `${options.context}: autostash cleanup dropped ${dropped}, preserved ${keptLive} live, failed ${failed}`,
+      entries.map((entry) => `${entry.kind} ${entry.sha.slice(0, 7)} (${entry.label})`).join("\n"),
+    ).catch(() => undefined);
+  }
+
+  return { dropped, keptLive, failed };
+}
+
 /**
  * AI fix-agent for autostash apply conflicts. Spawned only when applying
  * the stashed dev work hits a conflict — the merge has already committed
@@ -2221,6 +2325,44 @@ ${fileList}
  *      `git apply --3way` from the patch, fall through to AI patch-recovery
  *      if needed. See `tryRecoverHardFailApply`.
  */
+async function restoreRescueAutostashes(
+  rootDir: string,
+  taskId: string,
+  handle: AutostashHandle,
+  ctx: {
+    store: TaskStore;
+  },
+): Promise<{ unresolvedCount: number }> {
+  const rescueShas = handle.rescueShas ?? [];
+  if (rescueShas.length === 0) return { unresolvedCount: 0 };
+
+  let unresolvedCount = 0;
+  for (const rescue of rescueShas) {
+    try {
+      await execAsync(`git stash apply ${rescue.sha}`, { cwd: rootDir });
+      const dropResult = await dropAutostashBySha(rootDir, taskId, rescue.sha);
+      if (dropResult.dropped) {
+        mergerLog.log(`${taskId}: restored and dropped race-rescue autostash ${rescue.sha.slice(0, 7)} (${rescue.label})`);
+      } else {
+        unresolvedCount += 1;
+        mergerLog.warn(`${taskId}: restored race-rescue autostash ${rescue.sha.slice(0, 7)} but drop failed (${dropResult.reason ?? "unknown"})`);
+      }
+    } catch (err: unknown) {
+      unresolvedCount += 1;
+      const msg = err instanceof Error ? err.message : String(err);
+      mergerLog.warn(`${taskId}: race-rescue autostash apply failed for ${rescue.sha.slice(0, 7)} (${msg}); preserving stash for manual recovery`);
+    }
+  }
+
+  await ctx.store.logEntry(
+    taskId,
+    `Race-rescue autostash restore attempted: ${rescueShas.length - unresolvedCount} restored, ${unresolvedCount} preserved`,
+    rescueShas.map((r) => `${r.sha.slice(0, 7)} (${r.label})`).join("\n"),
+  ).catch(() => undefined);
+
+  return { unresolvedCount };
+}
+
 async function restoreUnrelatedRootDirChanges(
   rootDir: string,
   taskId: string,
@@ -5727,11 +5869,28 @@ export async function aiMergeTask(
         if (resultForFinally) {
           resultForFinally.autostash = outcome;
         }
+
+        const rescueRestore = outcome.status === "restored" || outcome.status === "ai-resolved"
+          ? await restoreRescueAutostashes(rootDir, taskId, autostashHandle, { store })
+          : { unresolvedCount: 0 };
+        const keepIfLive = outcome.status === "failed"
+          || outcome.status === "conflict-needs-manual"
+          || rescueRestore.unresolvedCount > 0;
+        await dropAutostashHandle(rootDir, taskId, autostashHandle, {
+          keepIfLive,
+          store,
+          context: "Post-restore autostash cleanup",
+        });
       } catch (err: unknown) {
         // Any throw from restore should never propagate out of the merger
         // — the merge result has already been recorded. Log and swallow.
         const msg = err instanceof Error ? err.message : String(err);
-        mergerLog.warn(`${taskId}: autostash restore threw unexpectedly (${msg}) — stash may be left in place; check git stash list`);
+        mergerLog.warn(`${taskId}: autostash restore threw unexpectedly (${msg}) — running keep-if-live cleanup sweep`);
+        await dropAutostashHandle(rootDir, taskId, autostashHandle, {
+          keepIfLive: true,
+          store,
+          context: "Autostash restore exception cleanup",
+        });
         if (resultForFinally) {
           resultForFinally.autostash = {
             status: "failed",

packages/engine/src/project-engine.ts

@@ -21,7 +21,7 @@ import { NotificationService } from "./notification/index.js";
 import { GridlockDetector } from "./gridlock-detector.js";
 import { CronRunner, createAiPromptExecutor } from "./cron-runner.js";
 import type { RoutineRunner } from "./routine-runner.js";
-import { aiMergeTask } from "./merger.js";
+import { aiMergeTask, sweepStaleAutostashes } from "./merger.js";
 import { PRIORITY_MERGE } from "./concurrency.js";
 import { runtimeLog } from "./logger.js";
 import type { HeartbeatTriggerScheduler } from "./agent-heartbeat.js";
@@ -170,6 +170,7 @@ export class ProjectEngine {
   private activeMergeTaskId: string | null = null;
   private mergeAbortController: AbortController | null = null;
   private mergeRetryTimer: ReturnType<typeof setTimeout> | null = null;
+  private autostashSweepTimer: ReturnType<typeof setTimeout> | null = null;
 
   /**
    * Pending manual merge resolvers — keyed by taskId.
@@ -444,6 +445,10 @@ export class ProjectEngine {
     // 8. Start periodic merge retry sweep
     this.scheduleMergeRetry(store);
 
+    // 9. Startup + periodic stale autostash sweeps (independent of autoMerge)
+    void this.runStaleAutostashSweep(store, "startup");
+    this.scheduleStaleAutostashSweep(store);
+
     this.started = true;
     runtimeLog.log(`ProjectEngine started for ${this.config.projectId}`);
   }
@@ -467,6 +472,10 @@ export class ProjectEngine {
       clearTimeout(this.mergeRetryTimer);
       this.mergeRetryTimer = null;
     }
+    if (this.autostashSweepTimer) {
+      clearTimeout(this.autostashSweepTimer);
+      this.autostashSweepTimer = null;
+    }
 
     // Abort active/pending merge work before tearing down sessions.
     this.mergeAbortController?.abort();
@@ -1920,6 +1929,44 @@ export class ProjectEngine {
     }
   }
 
+  private resolveAutostashMaxAgeMs(settings: Settings): number {
+    const hours = Math.max(1, Math.trunc(settings.mergerAutostashMaxAgeHours ?? 24));
+    return hours * 60 * 60 * 1000;
+  }
+
+  private async runStaleAutostashSweep(store: TaskStore, reason: "startup" | "periodic"): Promise<void> {
+    try {
+      const settings = await store.getSettings();
+      if (settings.globalPause || settings.enginePaused) return;
+      const maxAgeMs = this.resolveAutostashMaxAgeMs(settings);
+      const result = await sweepStaleAutostashes(this.config.workingDirectory, {
+        maxAgeMs,
+        taskStore: store,
+      });
+      if (result.dropped > 0) {
+        runtimeLog.log(`${reason === "startup" ? "Startup" : "Periodic"} stale autostash sweep dropped ${result.dropped} stash(es)`);
+      }
+    } catch (err: unknown) {
+      runtimeLog.warn(`Stale autostash ${reason} sweep failed: ${err instanceof Error ? err.message : String(err)}`);
+    }
+  }
+
+  private scheduleStaleAutostashSweep(store: TaskStore): void {
+    if (this.shuttingDown) return;
+    const schedule = async () => {
+      if (this.shuttingDown) return;
+      try {
+        await this.runStaleAutostashSweep(store, "periodic");
+      } finally {
+        if (!this.shuttingDown) {
+          this.autostashSweepTimer = setTimeout(() => void schedule(), 60 * 60 * 1000);
+        }
+      }
+    };
+
+    this.autostashSweepTimer = setTimeout(() => void schedule(), 60 * 60 * 1000);
+  }
+
   private scheduleMergeRetry(store: TaskStore): void {
     if (this.shuttingDown) return;