fix(client): preserve index-only snapshot state

tests/test_client.py

@@ -1346,6 +1346,54 @@ class TestCodexReviewFindings(GitScenarioBase):
         client.build_snapshot(self.local)
         self.assertEqual(run_git(self.local, "status", "--porcelain"), before)
 
+    def test_index_only_work_survives_a_pushed_snapshot(self):
+        """A staged version remains backed up when worktree bytes equal HEAD."""
+        self.write(self.local, "a.txt", "committed")
+        run_git(self.local, "add", "-A")
+        run_git(self.local, "commit", "-m", "base")
+        run_git(self.local, "push", "-u", "granthi", "main")
+        head_before = run_git(self.local, "rev-parse", "HEAD")
+
+        self.write(self.local, "a.txt", "INDEX-ONLY STAGED VERSION")
+        run_git(self.local, "add", "a.txt")
+        self.write(self.local, "a.txt", "committed")
+        status_before = run_git(self.local, "status", "--porcelain")
+        index_before = run_git(self.local, "write-tree")
+        with open(os.path.join(self.local, "a.txt")) as f:
+            file_before = f.read()
+        self.assertEqual(status_before, "MM a.txt")
+
+        ref = client.push_snapshot(self.local, "dev-index-only")
+
+        self.assertIsNotNone(ref)
+        snapshot = run_git(self.bare, "rev-parse", ref)
+        parents = run_git(self.bare, "log", "-1", "--format=%P", snapshot).split()
+        self.assertTrue(
+            any(run_git(self.bare, "show", f"{parent}:a.txt")
+                == "INDEX-ONLY STAGED VERSION" for parent in parents),
+            f"staged version unreachable from {parents}")
+        self.assertEqual(run_git(self.local, "rev-parse", "HEAD"), head_before)
+        self.assertEqual(run_git(self.local, "write-tree"), index_before)
+        self.assertEqual(run_git(self.local, "status", "--porcelain"), status_before)
+        with open(os.path.join(self.local, "a.txt")) as f:
+            self.assertEqual(f.read(), file_before)
+
+        self.write(self.local, "a.txt", "A NEW STAGED VERSION")
+        run_git(self.local, "add", "a.txt")
+        self.write(self.local, "a.txt", "committed")
+        second_ref = f"refs/granthi-backup/dev-index-only/second"
+        with mock.patch.object(client, "snapshot_ref",
+                               return_value=(second_ref, "second")):
+            self.assertEqual(
+                client.push_snapshot(self.local, "dev-index-only"), second_ref)
+        second = run_git(self.bare, "rev-parse", second_ref)
+        second_parents = run_git(
+            self.bare, "log", "-1", "--format=%P", second).split()
+        self.assertTrue(
+            any(run_git(self.bare, "show", f"{parent}:a.txt")
+                == "A NEW STAGED VERSION" for parent in second_parents),
+            f"updated staged version unreachable from {second_parents}")
+
     def test_a_truncated_listing_refuses_instead_of_guessing(self):
         """[P3] A name that is merely beyond the page cap must not resolve to a
         different repo that happens to exist under your own account."""