fix(models): exempt streaming sessions from Untitled+0-message sidebar filter (#1327)

From PR #1330.

Co-authored-by: Frank Song <franksong2702@gmail.com>

api/models.py

@@ -769,9 +769,16 @@ def all_sessions():
             # No grace window: a 0-message Untitled session is never shown in the list
             # regardless of age. This means page refreshes and accidental New Conversation
             # clicks never leave orphan entries in the sidebar.
+            #
+            # Exception: sessions with active_stream_id set are actively streaming (#1327).
+            # #1184 deferred the first save() until the first message, so during the
+            # initial streaming turn the session still looks like Untitled+0-messages.
+            # Without this exemption, navigating away during a long first turn causes
+            # the session to vanish from the sidebar.
             result = [s for s in result if not (
                 s.get('title', 'Untitled') == 'Untitled'
                 and s.get('message_count', 0) == 0
+                and not s.get('active_stream_id')
             )]
             result = [s for s in result if not _hide_from_default_sidebar(s)]
             # Backfill: sessions created before Sprint 22 have no profile tag.
@@ -796,10 +803,12 @@ def all_sessions():
     out.sort(key=lambda s: (getattr(s, 'pinned', False), _session_sort_timestamp(s)), reverse=True)
     # Hide empty Untitled sessions from the UI entirely — kept consistent with the
     # index-path filter above. No grace window: a 0-message Untitled session is
-    # never shown regardless of age (#1171).
+    # never shown regardless of age (#1171).  Same streaming exemption as above (#1327).
     result = [s.compact(include_runtime=True, active_stream_ids=active_stream_ids) for s in out if not (
         s.title == 'Untitled'
         and len(s.messages) == 0
+        and not s.active_stream_id
+        and not s.pending_user_message
     )]
     result = [s for s in result if not _hide_from_default_sidebar(s)]
     for s in result:

tests/test_streaming_session_sidebar.py

@@ -0,0 +1,167 @@
+"""
+Regression tests for #1327: streaming sessions must not vanish from sidebar.
+
+PR #1184 deferred the first save() until the session has real state. During the
+initial streaming turn, the session still looks like Untitled + 0-messages
+(title is derived later, user text is in pending_user_message not messages).
+The sidebar filter must exempt actively-streaming sessions from the empty-
+Untitled rule so they remain visible while the user navigates away.
+"""
+import pytest
+
+import api.models as models
+from api.models import (
+    SESSIONS,
+    STREAMS,
+    Session,
+    all_sessions,
+    new_session,
+)
+
+
+@pytest.fixture(autouse=True)
+def _isolate(tmp_path, monkeypatch):
+    """Redirect SESSION_DIR and SESSION_INDEX_FILE to a fresh tmp dir."""
+    session_dir = tmp_path / "sessions"
+    session_dir.mkdir()
+    index_file = session_dir / "_index.json"
+    monkeypatch.setattr(models, "SESSION_DIR", session_dir)
+    monkeypatch.setattr(models, "SESSION_INDEX_FILE", index_file)
+    SESSIONS.clear()
+    STREAMS.clear()
+    yield session_dir
+    SESSIONS.clear()
+    STREAMS.clear()
+
+
+# ── Helpers ────────────────────────────────────────────────────────────────
+
+
+def _simulate_first_turn_streaming(session):
+    """Simulate the state of a session during its first streaming turn.
+
+    After _handle_chat/start sets pending_user_message and calls save(),
+    but before the first assistant turn completes:
+    - title is still 'Untitled'
+    - messages is still empty (user text is in pending_user_message)
+    - active_stream_id is set
+    """
+    session.pending_user_message = "Hello, this is a long prompt"
+    session.active_stream_id = f"stream-{session.session_id}"
+    session.save()
+    # Register stream so _active_stream_ids() finds it
+    STREAMS[session.active_stream_id] = session.session_id
+
+
+# ── Index path (sidebar via index file) ────────────────────────────────────
+
+
+def test_streaming_session_visible_in_sidebar_index_path(_isolate):
+    """A session that is actively streaming its first turn must appear in
+    all_sessions() even though it is Untitled + 0-messages (#1327)."""
+    s = new_session()
+    _simulate_first_turn_streaming(s)
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id in ids, (
+        "Actively streaming session disappeared from sidebar (index path). "
+        "The Untitled+0-message filter must exempt sessions with active_stream_id."
+    )
+
+
+def test_empty_session_still_hidden_when_not_streaming(_isolate):
+    """A plain empty Untitled session (no stream, no pending message) must
+    still be hidden — the #1171 filter must not be weakened."""
+    s = new_session()
+    # No streaming state set — just a bare empty session
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id not in ids, (
+        "Empty Untitled session should still be hidden from sidebar. "
+        "Only actively streaming sessions are exempt (#1327)."
+    )
+
+
+# ── Full-scan fallback path ────────────────────────────────────────────────
+
+
+def test_streaming_session_visible_in_sidebar_fullscan(_isolate):
+    """Same as above but forces the full-scan fallback path by corrupting
+    the index file."""
+    s = new_session()
+    _simulate_first_turn_streaming(s)
+
+    # Corrupt the index to force the full-scan fallback
+    models.SESSION_INDEX_FILE.write_text("INVALID JSON")
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id in ids, (
+        "Actively streaming session disappeared from sidebar (full-scan path). "
+        "The Untitled+0-message filter must exempt sessions with "
+        "active_stream_id and pending_user_message."
+    )
+
+
+def test_empty_session_still_hidden_fullscan(_isolate):
+    """Empty Untitled session must still be hidden on the full-scan path."""
+    s = new_session()
+
+    models.SESSION_INDEX_FILE.write_text("INVALID JSON")
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id not in ids, (
+        "Empty Untitled session should still be hidden from sidebar (full-scan)."
+    )
+
+
+# ── Edge cases ────────────────────────────────────────────────────────────
+
+
+def test_session_visible_after_stream_completes(_isolate):
+    """After streaming completes and messages are populated, the session
+    must remain visible (message_count > 0)."""
+    s = new_session()
+    _simulate_first_turn_streaming(s)
+
+    # Simulate stream completion: clear pending, add messages
+    s.active_stream_id = None
+    s.pending_user_message = None
+    s.messages.append({"role": "user", "content": "Hello"})
+    s.messages.append({"role": "assistant", "content": "Hi there"})
+    s.title = "Greeting"
+    s.save()
+    STREAMS.pop(f"stream-{s.session_id}", None)
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id in ids, (
+        "Session with messages should be visible after stream completes."
+    )
+
+
+def test_pending_message_without_stream_still_visible(_isolate):
+    """A session with pending_user_message but no active_stream_id (edge case:
+    stream crashed after setting pending but before setting stream id) should
+    still be visible on the full-scan path."""
+    s = new_session()
+    s.pending_user_message = "Hello"
+    # No active_stream_id set
+    s.save()
+
+    models.SESSION_INDEX_FILE.write_text("INVALID JSON")
+
+    ids = {row["session_id"] for row in all_sessions()}
+    assert s.session_id in ids, (
+        "Session with pending_user_message should be visible even without "
+        "active_stream_id (full-scan path)."
+    )
+
+
+def test_compact_output_contains_active_stream_id(_isolate):
+    """Verify that compact() output includes active_stream_id so the index
+    path filter can check it."""
+    s = new_session()
+    s.active_stream_id = "test-stream-123"
+    compact = s.compact()
+    assert compact.get("active_stream_id") == "test-stream-123", (
+        "compact() must include active_stream_id for the sidebar filter."
+    )