fix(sync): fail-closed staging-dir ownership guard — prevent rm -rf of repo (#1802)

Adopts community fix #1827 by @diazMelgarejo (cyre). New lib/staging-guard.ts
exports checkOwnedStagingDir(), the single fail-closed predicate for 'safe to
recurse-delete or resume into', wired at cleanupStagingDir() (the deletion
chokepoint), decideResume(), the ingest entry point, and makeStagingDir()
(mints the .gstack-staging marker).

Fixes #1802.

Co-Authored-By: cyre <diazMelgarejo@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/regression-1611-gbrain-sync-resume.test.ts

@@ -35,6 +35,7 @@ import {
   readGbrainCheckpoint,
   decideResume,
 } from "../bin/gstack-gbrain-sync";
+import { checkOwnedStagingDir, STAGING_MARKER } from "../lib/staging-guard";
 
 const ROOT = path.resolve(import.meta.dir, "..");
 const DEFAULT_MS = 35 * 60 * 1000;
@@ -132,9 +133,11 @@ describe("#1611 decideResume — checkpoint + staging detection", () => {
     expect(decideResume().kind).toBe("no-checkpoint");
   });
 
-  test("checkpoint + staging dir exists → resume verdict", () => {
+  test("checkpoint + minted staging dir exists → resume verdict", () => {
     fs.mkdirSync(stagingDir, { recursive: true });
     fs.writeFileSync(stagingDir + "/page1.md", "content", "utf-8");
+    // #1802: a real staging dir carries the ownership marker minted by makeStagingDir.
+    fs.writeFileSync(path.join(stagingDir, STAGING_MARKER), "99\n99\n", "utf-8");
     fs.writeFileSync(cpPath, JSON.stringify({
       dir: stagingDir,
       totalFiles: 1989,
@@ -143,7 +146,8 @@ describe("#1611 decideResume — checkpoint + staging detection", () => {
       timestamp: "2026-05-19T19:30:05.008Z",
     }), "utf-8");
 
-    const v = decideResume();
+    // gstackHome is injected so the ownership check anchors on the test home.
+    const v = decideResume(tmpHome);
     expect(v.kind).toBe("resume");
     if (v.kind === "resume") {
       expect(v.stagingDir).toBe(stagingDir);
@@ -160,13 +164,41 @@ describe("#1611 decideResume — checkpoint + staging detection", () => {
       processedIndex: 1000,
     }), "utf-8");
 
-    const v = decideResume();
+    const v = decideResume(tmpHome);
     expect(v.kind).toBe("stale-staging-missing");
     if (v.kind === "stale-staging-missing") {
       expect(v.stagingDir).toBe(stagingDir);
     }
   });
 
+  // ── #1802 regression: poisoned checkpoint must never be adopted/deleted ────
+
+  test("#1802 checkpoint.dir = repo root with .git → stale-staging-missing (not resumed)", () => {
+    // Reproduces the exact poison: an interrupted import wrote checkpoint.dir =
+    // the repo working tree. It exists and is a directory, so the pre-#1802
+    // code resumed (and cleanup later rm -rf'd it). It must now be refused.
+    const repoRoot = path.join(tmpHome, "my-repo");
+    fs.mkdirSync(path.join(repoRoot, ".git"), { recursive: true });
+    fs.writeFileSync(path.join(repoRoot, "important.py"), "# real work\n", "utf-8");
+    fs.writeFileSync(cpPath, JSON.stringify({ dir: repoRoot, totalFiles: 10, processedIndex: 3 }), "utf-8");
+
+    const v = decideResume(tmpHome);
+    expect(v.kind).toBe("stale-staging-missing");
+    // decideResume never deletes, but prove the repo is untouched by the verdict.
+    expect(fs.existsSync(path.join(repoRoot, "important.py"))).toBe(true);
+  });
+
+  test("#1802 staging-named dir WITHOUT marker → stale-staging-missing (not minted by us)", () => {
+    fs.mkdirSync(stagingDir, { recursive: true }); // .staging-ingest-99-99, but no marker
+    fs.writeFileSync(cpPath, JSON.stringify({ dir: stagingDir, totalFiles: 1, processedIndex: 0 }), "utf-8");
+    expect(decideResume(tmpHome).kind).toBe("stale-staging-missing");
+  });
+
+  test("#1802 checkpoint.dir = '/' → stale-staging-missing", () => {
+    fs.writeFileSync(cpPath, JSON.stringify({ dir: "/", totalFiles: 1, processedIndex: 0 }), "utf-8");
+    expect(decideResume(tmpHome).kind).toBe("stale-staging-missing");
+  });
+
   test("checkpoint with no dir field → no-checkpoint verdict", () => {
     fs.writeFileSync(cpPath, JSON.stringify({
       totalFiles: 1989,
@@ -222,6 +254,99 @@ describe("#1611 SIGTERM staging preservation — static invariants", () => {
     );
     expect(body).toMatch(/GSTACK_INGEST_RESUME_DIR/);
     expect(body).toMatch(/resuming from gbrain checkpoint/);
-    expect(body).toMatch(/previous checkpoint stale.*staging dir.*gone.*restaging from scratch/);
+    expect(body).toMatch(/previous checkpoint stale/);
+    expect(body).toMatch(/restaging from scratch/);
+    // #1802: the caller distinguishes "refused as unowned" from "actually gone".
+    expect(body).toMatch(/staging dir not usable/);
+  });
+});
+
+// ── #1802 checkOwnedStagingDir — fail-closed ownership matrix ───────────────
+// The single predicate guarding both the resume gate (decideResume) and the
+// deletion chokepoint (cleanupStagingDir). Every branch is fail-closed: any
+// case it cannot prove is owned must return ok:false.
+describe("#1802 checkOwnedStagingDir — ownership matrix", () => {
+  let home: string;
+
+  beforeEach(() => {
+    home = fs.mkdtempSync(path.join(os.tmpdir(), "gstack-1802-"));
+  });
+  afterEach(() => {
+    try { fs.rmSync(home, { recursive: true, force: true }); } catch { /* best-effort */ }
+  });
+
+  function mintStaging(name = ".staging-ingest-1-1"): string {
+    const d = path.join(home, name);
+    fs.mkdirSync(d, { recursive: true });
+    fs.writeFileSync(path.join(d, STAGING_MARKER), "1\n1\n", "utf-8");
+    return d;
+  }
+
+  test("minted staging dir → ok", () => {
+    expect(checkOwnedStagingDir(mintStaging(), home).ok).toBe(true);
+  });
+
+  test("repo root (direct child, has .git, no marker) → refused", () => {
+    const repo = path.join(home, "my-repo");
+    fs.mkdirSync(path.join(repo, ".git"), { recursive: true });
+    expect(checkOwnedStagingDir(repo, home).ok).toBe(false);
+  });
+
+  test("staging-named dir containing .git → refused by tripwire even with marker", () => {
+    const d = mintStaging(".staging-ingest-9-9");
+    fs.mkdirSync(path.join(d, ".git"), { recursive: true });
+    const v = checkOwnedStagingDir(d, home);
+    expect(v.ok).toBe(false);
+    expect(v.reason).toMatch(/\.git/);
+  });
+
+  test("staging-named dir without marker → refused (not minted)", () => {
+    const d = path.join(home, ".staging-ingest-2-2");
+    fs.mkdirSync(d, { recursive: true });
+    expect(checkOwnedStagingDir(d, home).ok).toBe(false);
+  });
+
+  test("right name but NOT a direct child of home → refused", () => {
+    const nested = path.join(home, "sub", ".staging-ingest-3-3");
+    fs.mkdirSync(nested, { recursive: true });
+    fs.writeFileSync(path.join(nested, STAGING_MARKER), "x", "utf-8");
+    expect(checkOwnedStagingDir(nested, home).ok).toBe(false);
+  });
+
+  test("direct child of home but wrong name → refused", () => {
+    const d = path.join(home, "notstaging");
+    fs.mkdirSync(d, { recursive: true });
+    fs.writeFileSync(path.join(d, STAGING_MARKER), "x", "utf-8");
+    expect(checkOwnedStagingDir(d, home).ok).toBe(false);
+  });
+
+  test("missing path → refused (unresolvable)", () => {
+    expect(checkOwnedStagingDir(path.join(home, ".staging-ingest-gone"), home).ok).toBe(false);
+  });
+
+  test("'/' and '' → refused", () => {
+    expect(checkOwnedStagingDir("/", home).ok).toBe(false);
+    expect(checkOwnedStagingDir("", home).ok).toBe(false);
+  });
+
+  test("symlink whose target escapes home → refused (realpath resolves first)", () => {
+    const outside = path.join(home, "..", path.basename(home) + "-outside");
+    fs.mkdirSync(outside, { recursive: true });
+    const link = path.join(home, ".staging-ingest-link");
+    fs.symlinkSync(outside, link);
+    try {
+      // realpathSync resolves the link to `outside`, whose parent is not `home`.
+      expect(checkOwnedStagingDir(link, home).ok).toBe(false);
+    } finally {
+      try { fs.rmSync(outside, { recursive: true, force: true }); } catch { /* best-effort */ }
+    }
+  });
+
+  test("cleanupStagingDir + decideResume both call the guard (static invariant)", () => {
+    const ingest = fs.readFileSync(path.join(ROOT, "bin", "gstack-memory-ingest.ts"), "utf-8");
+    const sync = fs.readFileSync(path.join(ROOT, "bin", "gstack-gbrain-sync.ts"), "utf-8");
+    expect(ingest).toMatch(/checkOwnedStagingDir\(dir, GSTACK_HOME\)/);
+    expect(ingest).toMatch(/staging cleanup REFUSED/);
+    expect(sync).toMatch(/checkOwnedStagingDir\(stagingDir, gstackHome\)/);
   });
 });