diff --git a/routes/chat_routes.py b/routes/chat_routes.py
index 764c7e0..8df0af0 100644
--- a/routes/chat_routes.py
+++ b/routes/chat_routes.py
@@ -436,10 +436,11 @@ def setup_chat_routes(
                 else:
                     logger.warning(f"[doc-inject] NOT FOUND by ID {active_doc_id}")
             if not active_doc:
-                active_doc = _doc_db.query(DBDocument).filter(
+                _session_doc_q = _doc_db.query(DBDocument).filter(
                     DBDocument.session_id == session,
                     DBDocument.is_active == True
-                ).order_by(DBDocument.updated_at.desc()).first()
+                )
+                active_doc = _owner_session_filter(_session_doc_q, ctx.user).order_by(DBDocument.updated_at.desc()).first()
                 if active_doc:
                     logger.info(f"[doc-inject] found by session fallback: title={active_doc.title!r}")
             # Last resort: the document the agent itself just created/edited
@@ -453,7 +454,8 @@ def setup_chat_routes(
                     from src.tool_implementations import get_active_document
                     _mem_id = get_active_document()
                     if _mem_id:
-                        cand = _doc_db.query(DBDocument).filter(DBDocument.id == _mem_id).first()
+                        _mem_q = _doc_db.query(DBDocument).filter(DBDocument.id == _mem_id)
+                        cand = _owner_session_filter(_mem_q, ctx.user).first()
                         if cand and (not cand.session_id or cand.session_id == session):
                             active_doc = cand
                             logger.info(f"[doc-inject] found by in-memory active id: title={active_doc.title!r} (session_id={cand.session_id!r})")
diff --git a/tests/test_security_regressions.py b/tests/test_security_regressions.py
index 488c38f..6b3a691 100644
--- a/tests/test_security_regressions.py
+++ b/tests/test_security_regressions.py
@@ -947,14 +947,18 @@ def test_chat_active_document_lookup_is_owner_scoped():
     """The explicit `active_doc_id` path in /api/chat_stream must scope the
     document lookup to the caller. Resolving by id alone let any user inject
     another user's document into their own chat context (the session and
-    in-memory fallbacks were already owner/session-bound; this branch wasn't)."""
+    in-memory fallbacks also need the same owner gate because active document
+    state is process-global)."""
     import re
 
     src = Path(__file__).resolve().parents[1] / "routes" / "chat_routes.py"
     text = src.read_text()
     # The frontend-supplied id is resolved through the shared owner filter.
     assert "_owner_session_filter(_doc_q, ctx.user)" in text
+    assert "_owner_session_filter(_session_doc_q, ctx.user)" in text
+    assert "_owner_session_filter(_mem_q, ctx.user)" in text
     # And never by id alone (the previous IDOR shape, whitespace-insensitive).
     flat = re.sub(r"\s+", " ", text)
     assert "filter( DBDocument.id == active_doc_id, ).first()" not in flat
     assert "filter(DBDocument.id == active_doc_id).first()" not in flat
+    assert "filter(DBDocument.id == _mem_id).first()" not in flat