diff --git a/api/models.py b/api/models.py
index ef039e5..c70886d 100644
--- a/api/models.py
+++ b/api/models.py
@@ -20,6 +20,25 @@ from api.workspace import get_last_workspace
 logger = logging.getLogger(__name__)
 
 
+def _index_entry_exists(session_id: str, in_memory_ids=None) -> bool:
+    """Return True if an index entry still has backing state.
+
+    A session can legitimately exist either as a persisted JSON file or as an
+    in-memory Session object that has not been flushed yet.  This helper is used
+    to prune stale `_index.json` rows left behind after session-id rotation or
+    file removal.
+    """
+    if not session_id:
+        return False
+    if in_memory_ids is None:
+        with LOCK:
+            in_memory_ids = set(SESSIONS.keys())
+    if session_id in in_memory_ids:
+        return True
+    p = SESSION_DIR / f'{session_id}.json'
+    return p.exists()
+
+
 def _write_session_index(updates=None):
     """Update the session index file.
 
@@ -56,6 +75,11 @@ def _write_session_index(updates=None):
     try:
         with LOCK:
             existing = json.loads(SESSION_INDEX_FILE.read_text(encoding='utf-8'))
+            in_memory_ids = set(SESSIONS.keys())
+            existing = [
+                e for e in existing
+                if _index_entry_exists(e.get('session_id'), in_memory_ids=in_memory_ids)
+            ]
             # Build lookup of updated entries
             updated_map = {s.session_id: s.compact() for s in updates}
             existing_ids = {e.get('session_id') for e in existing}
@@ -212,6 +236,10 @@ def all_sessions():
     if SESSION_INDEX_FILE.exists():
         try:
             index = json.loads(SESSION_INDEX_FILE.read_text(encoding='utf-8'))
+            index = [
+                s for s in index
+                if _index_entry_exists(s.get('session_id'))
+            ]
             # Overlay any in-memory sessions that may be newer than the index
             index_map = {s['session_id']: s for s in index}
             with LOCK:
diff --git a/tests/test_session_index.py b/tests/test_session_index.py
index 92846b8..f4702ae 100644
--- a/tests/test_session_index.py
+++ b/tests/test_session_index.py
@@ -146,6 +146,38 @@ def test_new_session_appended_to_index():
     assert "sess_b" in ids
 
 
+def test_incremental_update_prunes_stale_entries():
+    """Ghost rows whose backing JSON file is gone must be dropped on the fast path.
+
+    This covers session-id rotation paths (e.g. compression) where the old id can
+    linger in `_index.json` after the file has been renamed.
+    """
+    index_file = models.SESSION_INDEX_FILE
+
+    stale = {
+        "session_id": "ghost_sid",
+        "title": "Ghost",
+        "updated_at": 150.0,
+        "workspace": "/tmp",
+        "model": "test",
+        "message_count": 1,
+        "created_at": 100.0,
+        "pinned": False,
+        "archived": False,
+    }
+    _write_index_file(index_file, [stale])
+
+    sA = _make_session("sess_a", "Alpha", updated_at=200.0)
+    sA.path.write_text(json.dumps(sA.__dict__, ensure_ascii=False, indent=2), encoding="utf-8")
+
+    _write_session_index(updates=[sA])
+
+    index = _read_index(index_file)
+    ids = {e["session_id"] for e in index}
+    assert "sess_a" in ids
+    assert "ghost_sid" not in ids, "stale entry with no backing file must be pruned"
+
+
 # ── 8. test_first_call_full_rebuild ──────────────────────────────────────
 
 def test_first_call_full_rebuild():
@@ -348,3 +380,33 @@ def test_deadlock_guard_on_fallback():
     # The index should still be valid after fallback
     index = _read_index(index_file)
     assert isinstance(index, list)
+
+
+def test_all_sessions_ignores_stale_index_entries():
+    """Reading via all_sessions() must not surface ghost rows from _index.json."""
+    index_file = models.SESSION_INDEX_FILE
+
+    valid_session = _make_session("sess_a", "Alpha", updated_at=200.0)
+    valid_session.path.write_text(
+        json.dumps(valid_session.__dict__, ensure_ascii=False, indent=2),
+        encoding="utf-8",
+    )
+
+    valid = valid_session.compact()
+    stale = {
+        "session_id": "ghost_sid",
+        "title": "Ghost",
+        "updated_at": 150.0,
+        "workspace": "/tmp",
+        "model": "test",
+        "message_count": 1,
+        "created_at": 100.0,
+        "pinned": False,
+        "archived": False,
+    }
+    _write_index_file(index_file, [stale, valid])
+
+    rows = models.all_sessions()
+    ids = {e["session_id"] for e in rows}
+    assert "sess_a" in ids
+    assert "ghost_sid" not in ids