fix(delegate): title subagent sessions after their goal without a model call

agent/title_generator.py

@@ -606,6 +606,18 @@ def _persist_session_title(session_db, session_id, title, *, source, dedupe=True
         return _set(deduped)
 
 
+def apply_subagent_title(session_db, session_id: str, goal: str) -> Optional[str]:
+    """Title a delegate run ``Subagent: <goal's first line>`` at ``derived`` authority. No model call:
+    runs fan out in bulk, and the prefix alone is what tells them apart from conversations wherever
+    ``sessions.show_subagents`` lists them (#97202). Collisions get ``#N``. Never raises."""
+    try:
+        derived = derive_title(goal) if is_titleable_user_message(goal) else None
+        return _persist_session_title(session_db, session_id, f"Subagent: {derived}", source="derived") if derived else None
+    except Exception:
+        logger.debug("Subagent title failed for %s", session_id, exc_info=True)
+        return None
+
+
 def apply_instant_title(
     session_db, session_id: str, user_message: str, title_callback: Optional[TitleCallback] = None,
     title_preview: str | None = None,

agent/turn_context.py

@@ -157,9 +157,9 @@ def append_notes_to_multimodal_content(content: Any, notes: Optional[str]) -> bo
     return False
 
 
-# Surfaces whose sessions must not be auto-titled: cron names its own session and
-# its opener is a delivery hint; subagent sessions are hidden from every picker.
-_UNTITLED_PLATFORMS = frozenset({"cron", "subagent"})
+# Cron sessions are never auto-titled: cron names its own session and its opener is a delivery hint.
+# Subagent runs get a cheap ``Subagent: <goal>`` title instead of a model call (apply_subagent_title).
+_UNTITLED_PLATFORMS = frozenset({"cron"})
 
 
 def _maybe_title_session_at_turn_start(agent: Any, messages: List[Any]) -> None:
@@ -168,11 +168,12 @@ def _maybe_title_session_at_turn_start(agent: Any, messages: List[Any]) -> None:
     session_id = getattr(agent, "session_id", None)
     if not session_db or not session_id:
         return
-    if str(getattr(agent, "platform", "") or "").lower() in _UNTITLED_PLATFORMS:
+    platform = str(getattr(agent, "platform", "") or "").lower()
+    if platform in _UNTITLED_PLATFORMS:
         return
     try:
         from agent.message_content import flatten_message_text
-        from agent.title_generator import maybe_auto_title
+        from agent.title_generator import apply_subagent_title, maybe_auto_title
 
         # Turn's user message as text; image-only turns yield "" and are skipped.
         user_text = ""
@@ -194,6 +195,9 @@ def _maybe_title_session_at_turn_start(agent: Any, messages: List[Any]) -> None:
                 ensure()
             if not getattr(agent, "_session_db_created", False):
                 return
+        if platform == "subagent":
+            apply_subagent_title(session_db, session_id, user_text)
+            return
         # Snapshot runtime identity so the background titler can skip if the user
         # switches models before it fires.
         # ``session_id`` rides along so the background titler's OpenCode request carries the

tests/agent/test_turn_context.py

@@ -506,6 +506,29 @@ def test_prologue_does_not_title_machine_driven_runs(platform):
     assert not _title_turn(platform).called
 
 
+def test_prologue_names_a_subagent_run_after_its_goal_without_a_model_call():
+    """A delegate run gets ``Subagent: <goal>`` at derived authority so it reads as machinery
+    wherever ``sessions.show_subagents`` lists it, instead of staying untitled (#97202)."""
+    from agent import turn_context
+
+    agent = _TitlingAgent("subagent")
+    agent._session_db.set_auto_title.return_value = True
+    with patch("agent.title_generator.maybe_auto_title") as titler:
+        turn_context._maybe_title_session_at_turn_start(
+            agent, [{"role": "user", "content": "Audit the billing module\n\nContext: ..."}])
+    assert not titler.called
+    agent._session_db.set_auto_title.assert_called_once_with(
+        "sess-1", "Subagent: Audit the billing module", source="derived")
+
+
+def test_prologue_leaves_cron_runs_untitled():
+    agent = _TitlingAgent("cron")
+    from agent import turn_context
+
+    turn_context._maybe_title_session_at_turn_start(agent, [{"role": "user", "content": "Run the job"}])
+    assert not agent._session_db.set_auto_title.called
+
+
 def test_prologue_forwards_the_submit_title_preview_to_the_titler():
     """A paste-shrunk ``display_metadata.title_preview`` from prompt.submit is the text the
     titler should read, not the full pasted body."""