diff --git a/gitnexus/src/core/shared-store-analyze.ts b/gitnexus/src/core/shared-store-analyze.ts
index 2f2b91fa0..1817d72ae 100644
--- a/gitnexus/src/core/shared-store-analyze.ts
+++ b/gitnexus/src/core/shared-store-analyze.ts
@@ -20,7 +20,7 @@ import { existsSync, constants as fsConstants } from 'fs';
 import fs from 'fs/promises';
 import path from 'path';
 import { acquireIndexLock, requireExclusiveIndexLock } from '../storage/index-lock.js';
-import { commitDistanceToHead, getRemoteUrl, isWorkingTreeDirty } from '../storage/git.js';
+import { commitDistanceToHead, getRemoteUrl, isWorkingTreePristine } from '../storage/git.js';
 import {
   canonicalizePath,
   findRegistryEntryByRepoPath,
@@ -168,7 +168,10 @@ const listCommitGraphs = async (layout: SharedStoreLayout): Promise<CommitGraph[
  * ponytail: one `git` call pair per commit graph; fine for tens of graphs,
  * batch through `git rev-list` if stores grow to hundreds.
  */
-const pickSeed = (repoPath: string, graphs: CommitGraph[]): CommitGraph | null => {
+const pickSeed = (
+  repoPath: string,
+  graphs: CommitGraph[],
+): { graph: CommitGraph; distance: number } | null => {
   let best: { graph: CommitGraph; distance: number } | null = null;
   for (const graph of graphs) {
     const distance = commitDistanceToHead(repoPath, graph.commit);
@@ -179,7 +182,7 @@ const pickSeed = (repoPath: string, graphs: CommitGraph[]): CommitGraph | null =
       (distance === best.distance && graph.meta.indexedAt > best.graph.meta.indexedAt);
     if (better) best = { graph, distance };
   }
-  return best?.graph ?? null;
+  return best;
 };
 
 /**
@@ -251,7 +254,12 @@ export const seedSharedSlot = async (
   log: Log,
 ): Promise<void> => {
   if (await loadMeta(layout.checkoutSlot)) return;
-  const seed = pickSeed(repoPath, await listCommitGraphs(layout));
+  const picked = pickSeed(repoPath, await listCommitGraphs(layout));
+  const seed = picked?.graph;
+  // A commit graph matches its commit exactly, so a checkout showing exactly
+  // that commit is up to date. Any other checkout gets an empty lastCommit,
+  // like seedFromLocalIndex, so its next run hash-diffs.
+  const upToDate = picked?.distance === 0 && isWorkingTreePristine(repoPath);
   // Record the pointer under the publish lock, where reclaim counts
   // references, so the graph cannot be deleted between the pick and the save.
   const pointed =
@@ -265,6 +273,7 @@ export const seedSharedSlot = async (
         repoPath,
         storagePath: layout.checkoutSlot,
         graphPath: graph,
+        lastCommit: upToDate ? seed.meta.lastCommit : '',
       };
       delete meta.incrementalInProgress;
       await saveMeta(layout.checkoutSlot, meta);
@@ -361,7 +370,8 @@ export const publishSharedGraph = async (
     meta.lastCommit === currentCommit &&
     !meta.incrementalInProgress &&
     builtClean &&
-    !isWorkingTreeDirty(repoPath);
+    // A sparse or partial checkout builds a graph missing the files it hides.
+    isWorkingTreePristine(repoPath);
   // Every pointer change and the reclaim that follows run under one publish
   // lock, so a concurrent reclaim never sees a half-recorded reference.
   await withStoreLock(layout, 'publish', async () => {
diff --git a/gitnexus/src/storage/git.ts b/gitnexus/src/storage/git.ts
index baecaddfb..945439fcc 100644
--- a/gitnexus/src/storage/git.ts
+++ b/gitnexus/src/storage/git.ts
@@ -121,6 +121,33 @@ export const listWorkingTreeDirtyPaths = (repoPath: string): string[] | null =>
   }
 };
 
+/**
+ * True when the working tree shows exactly the committed tree: nothing dirty
+ * or untracked, no path hidden by skip-worktree or assume-unchanged (which is
+ * how a sparse checkout leaves files out), and every gitlink checked out as a
+ * submodule. `git status` stays clean in all three hidden cases. False on any
+ * git failure.
+ */
+export const isWorkingTreePristine = (repoPath: string): boolean => {
+  if (listWorkingTreeDirtyPaths(repoPath)?.length !== 0) return false;
+  try {
+    const out = execFileSync('git', ['ls-files', '--stage', '-z', '--'], {
+      cwd: repoPath,
+      windowsHide: true,
+      ...gitPathListExec,
+    });
+    for (const record of out.split('\0')) {
+      // `<mode> <object> <stage>\t<path>`; mode 160000 is a gitlink.
+      if (!record.startsWith('160000 ')) continue;
+      const rel = record.slice(record.indexOf('\t') + 1);
+      if (!existsSync(path.join(repoPath, rel, '.git'))) return false;
+    }
+    return true;
+  } catch {
+    return false;
+  }
+};
+
 /**
  * Snapshot, per candidate file, whether it is safe for `selfCommitContextFiles`
  * to auto-commit — call this BEFORE `analyze` writes AGENTS.md/CLAUDE.md.
diff --git a/gitnexus/test/integration/shared-store-analyze.test.ts b/gitnexus/test/integration/shared-store-analyze.test.ts
index 73867212e..4ef69c003 100644
--- a/gitnexus/test/integration/shared-store-analyze.test.ts
+++ b/gitnexus/test/integration/shared-store-analyze.test.ts
@@ -3,7 +3,12 @@ import { existsSync } from 'fs';
 import fs from 'fs/promises';
 import path from 'path';
 import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it } from 'vitest';
-import { featureKeyOf, publishSharedGraph } from '../../src/core/shared-store-analyze.js';
+import {
+  ensurePrivateSharedGraph,
+  featureKeyOf,
+  publishSharedGraph,
+  seedSharedSlot,
+} from '../../src/core/shared-store-analyze.js';
 import {
   getStoragePaths,
   listRegisteredRepos,
@@ -333,4 +338,56 @@ describe('publishSharedGraph race (#3352)', () => {
     expect(await listCommitDirs(layoutOf(main))).toEqual([]);
     expect(existsSync(path.join(layoutOf(main).checkoutSlot, 'lbug'))).toBe(true);
   });
+
+  // #3374: `git status` is clean in a sparse checkout, but the graph lacks the
+  // files the checkout leaves out.
+  it('keeps a checkout that hides committed files private', async () => {
+    const { checkouts, head } = await setup();
+    const [main] = checkouts;
+    git(main, 'update-index', '--skip-worktree', '--', 'a.ts');
+    await fs.rm(path.join(main, 'a.ts'));
+    await publishSharedGraph(layoutOf(main), main, head, () => {});
+    expect(await listCommitDirs(layoutOf(main))).toEqual([]);
+    expect(existsSync(path.join(layoutOf(main).checkoutSlot, 'lbug'))).toBe(true);
+  });
+
+  const seedFreshSlot = async (checkout: string): Promise<RepoMeta | null> => {
+    const layout = layoutOf(checkout);
+    await fs.rm(layout.checkoutSlot, { recursive: true, force: true });
+    await seedSharedSlot(layout, checkout, () => {});
+    return loadMeta(layout.checkoutSlot);
+  };
+
+  it('seeds a pristine checkout at the graph commit as up to date', async () => {
+    const { checkouts, head } = await setup();
+    const [main, wt] = checkouts;
+    await publishSharedGraph(layoutOf(main), main, head, () => {});
+    const seeded = await seedFreshSlot(wt);
+    expect(seeded?.graphPath).toBe((await loadMeta(layoutOf(main).checkoutSlot))?.graphPath);
+    expect(seeded?.lastCommit).toBe(head);
+  });
+
+  it('seeds a checkout that hides committed files without a commit, then re-points', async () => {
+    const { checkouts, head } = await setup();
+    const [main, wt] = checkouts;
+    await publishSharedGraph(layoutOf(main), main, head, () => {});
+    const shared = (await loadMeta(layoutOf(main).checkoutSlot))?.graphPath;
+    git(wt, 'update-index', '--skip-worktree', '--', 'a.ts');
+    const seeded = await seedFreshSlot(wt);
+    expect(seeded?.graphPath).toBe(shared);
+    // An empty lastCommit sends the next analyze through the file-hash diff.
+    expect(seeded?.lastCommit).toBe('');
+
+    // That analyze copies the graph, finds nothing to change, and stamps HEAD;
+    // once the checkout shows every file again, publish drops the copy.
+    const slot = layoutOf(wt).checkoutSlot;
+    expect(await ensurePrivateSharedGraph(slot, () => {})).toBe(true);
+    const copied = await loadMeta(slot);
+    expect(copied).not.toBeNull();
+    await saveMeta(slot, { ...(copied as RepoMeta), lastCommit: head });
+    git(wt, 'update-index', '--no-skip-worktree', '--', 'a.ts');
+    await publishSharedGraph(layoutOf(wt), wt, head, () => {});
+    expect((await loadMeta(slot))?.graphPath).toBe(shared);
+    expect(existsSync(path.join(slot, 'lbug'))).toBe(false);
+  });
 });
diff --git a/gitnexus/test/unit/git-utils.test.ts b/gitnexus/test/unit/git-utils.test.ts
index a5cb94083..ccbb1d06d 100644
--- a/gitnexus/test/unit/git-utils.test.ts
+++ b/gitnexus/test/unit/git-utils.test.ts
@@ -1135,3 +1135,122 @@ describe('listWorkingTreeDirtyPaths', () => {
     },
   );
 });
+
+// ─── isWorkingTreePristine ────────────────────────────────────────────────
+//
+// The shared-store publish gate (#3374): a graph built from a working tree
+// that hides committed content (sparse checkout, index bits, an uninitialized
+// submodule) must never become the commit graph other checkouts reuse.
+
+/** A repo with one committed file, `a.ts`. */
+function makeCommittedRepo(): string {
+  const repo = makeIsolatedGitRepo();
+  fs.writeFileSync(path.join(repo, 'a.ts'), 'export const a = 1;');
+  fs.mkdirSync(path.join(repo, 'lib'));
+  fs.writeFileSync(path.join(repo, 'lib', 'b.ts'), 'export const b = 1;');
+  execFileSync(gitExecutable, ['add', '-A'], { cwd: repo, stdio: 'ignore' });
+  execFileSync(gitExecutable, ['commit', '-q', '-m', 'init'], { cwd: repo, stdio: 'ignore' });
+  return repo;
+}
+
+const gitIn = (repo: string, ...args: string[]): string =>
+  execFileSync(gitExecutable, args, { cwd: repo, encoding: 'utf8' }).trim();
+
+describe('isWorkingTreePristine', () => {
+  it('is true for a clean checkout, ignoring GitNexus-managed writes', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const repo = makeCommittedRepo();
+    try {
+      fs.mkdirSync(path.join(repo, '.gitnexus'));
+      fs.writeFileSync(path.join(repo, '.gitnexus', 'meta.json'), '{}');
+      fs.writeFileSync(path.join(repo, 'AGENTS.md'), 'x');
+
+      expect(isWorkingTreePristine(repo)).toBe(true);
+    } finally {
+      fs.rmSync(repo, { recursive: true, force: true });
+    }
+  });
+
+  it('is false with an untracked source file', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const repo = makeCommittedRepo();
+    try {
+      fs.writeFileSync(path.join(repo, 'new.ts'), 'export const n = 1;');
+
+      expect(isWorkingTreePristine(repo)).toBe(false);
+    } finally {
+      fs.rmSync(repo, { recursive: true, force: true });
+    }
+  });
+
+  it.each(['--assume-unchanged', '--skip-worktree'])(
+    'is false when git update-index %s hides a path, even with unchanged content',
+    async (flag) => {
+      const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+      const repo = makeCommittedRepo();
+      try {
+        gitIn(repo, 'update-index', flag, '--', 'a.ts');
+
+        expect(isWorkingTreePristine(repo)).toBe(false);
+      } finally {
+        fs.rmSync(repo, { recursive: true, force: true });
+      }
+    },
+  );
+
+  it('is false in a sparse checkout that leaves committed files out', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const repo = makeCommittedRepo();
+    try {
+      gitIn(repo, 'sparse-checkout', 'set', '--no-cone', '/a.ts');
+
+      expect(fs.existsSync(path.join(repo, 'lib', 'b.ts'))).toBe(false);
+      expect(isWorkingTreePristine(repo)).toBe(false);
+    } finally {
+      fs.rmSync(repo, { recursive: true, force: true });
+    }
+  });
+
+  it('is false with a registered but uninitialized submodule', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const repo = makeCommittedRepo();
+    try {
+      const head = gitIn(repo, 'rev-parse', 'HEAD');
+      gitIn(repo, 'update-index', '--add', '--cacheinfo', `160000,${head},vendor/dep`);
+      gitIn(repo, 'commit', '-q', '-m', 'add gitlink');
+
+      expect(isWorkingTreePristine(repo)).toBe(false);
+    } finally {
+      fs.rmSync(repo, { recursive: true, force: true });
+    }
+  });
+
+  it('is true with a checked-out submodule', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const repo = makeCommittedRepo();
+    try {
+      const sub = path.join(repo, 'vendor', 'dep');
+      fs.mkdirSync(sub, { recursive: true });
+      gitIn(sub, 'init', '-q');
+      fs.writeFileSync(path.join(sub, 'c.ts'), 'export const c = 1;');
+      gitIn(sub, 'add', '-A');
+      gitIn(sub, '-c', 'user.name=t', '-c', 'user.email=t@t', 'commit', '-q', '-m', 'sub');
+      gitIn(repo, 'add', 'vendor/dep');
+      gitIn(repo, 'commit', '-q', '-m', 'add submodule');
+
+      expect(isWorkingTreePristine(repo)).toBe(true);
+    } finally {
+      fs.rmSync(repo, { recursive: true, force: true });
+    }
+  });
+
+  it('is false (fails closed) outside a git repository', async () => {
+    const { isWorkingTreePristine } = await import('../../src/storage/git.js');
+    const dir = makeIsolatedTempDir('gn-nongit-pristine-');
+    try {
+      expect(isWorkingTreePristine(dir)).toBe(false);
+    } finally {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  });
+});