fix(title): publish conversation context for aux title calls

Title generation via the aux client ran without the Agent's ambient
conversation context, so relay targets that key on it (OpenCode Go)
rejected the completion call with HTTP 400.

Publish the webui session id as the Agent conversation context around
the aux completion (restoring it in a finally block) and pass it from
all three title entry paths: background update, background refresh and
the on-demand regenerate helper.

Refs #7470

api/streaming.py

@@ -4560,7 +4560,7 @@ def _generate_llm_session_title_for_agent(agent, user_text: str, assistant_text:
     return None, 'llm_invalid', str(raw)[:120]
 
 
-def _generate_llm_session_title_via_aux(user_text: str, assistant_text: str, agent=None, *, use_agent_model: bool = False) -> tuple[Optional[str], str, str]:
+def _generate_llm_session_title_via_aux(user_text: str, assistant_text: str, agent=None, *, use_agent_model: bool = False, conversation_id: str = '') -> tuple[Optional[str], str, str]:
     """Generate a title via dedicated auxiliary LLM route, then sanitize/validate result.
 
     When use_agent_model is False (default), the auxiliary client resolves
@@ -4568,6 +4568,11 @@ def _generate_llm_session_title_via_aux(user_text: str, assistant_text: str, age
     prevents the session's chat model (e.g. a Chinese model) from overriding
     the dedicated title model.  When True, the agent's attrs are passed through
     (legacy fallback behaviour).
+
+    conversation_id republishes the webui session id as the Agent's ambient
+    conversation context for the duration of the aux call, so OpenCode relay
+    targets receive the same ``x-opencode-session`` sticky key as the session's
+    main turns (#7470). The context is reset in all exit paths.
     """
     if use_agent_model and agent:
         provider = getattr(agent, 'provider', '')
@@ -4577,13 +4582,30 @@ def _generate_llm_session_title_via_aux(user_text: str, assistant_text: str, age
         provider = ''
         model = ''
         base_url = ''
-    raw, status = generate_title_raw_via_aux(
-        user_text,
-        assistant_text,
-        provider=provider,
-        model=model,
-        base_url=base_url,
-    )
+    ctx_token = None
+    if conversation_id:
+        try:
+            from agent.portal_tags import set_conversation_context
+            ctx_token = set_conversation_context(str(conversation_id))
+        except Exception:
+            # Older/absent agent runtime: proceed without conversation context
+            # (previous behaviour) rather than failing title generation.
+            ctx_token = None
+    try:
+        raw, status = generate_title_raw_via_aux(
+            user_text,
+            assistant_text,
+            provider=provider,
+            model=model,
+            base_url=base_url,
+        )
+    finally:
+        if ctx_token is not None:
+            try:
+                from agent.portal_tags import reset_conversation_context
+                reset_conversation_context(ctx_token)
+            except Exception:
+                pass
     if not raw:
         return None, status, ''
     title = _sanitize_generated_title(raw)
@@ -4733,9 +4755,9 @@ def _run_background_title_update(session_id: str, user_text: str, assistant_text
             if agent and not aux_title_configured:
                 next_title, llm_status, raw_preview = _generate_llm_session_title_for_agent(agent, user_text, assistant_text)
                 if not next_title and llm_status in ('llm_error', 'llm_invalid'):
-                    next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent, use_agent_model=True)
+                    next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent, use_agent_model=True, conversation_id=session_id)
             else:
-                next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text)
+                next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, conversation_id=session_id)
                 if not next_title and agent and llm_status in ('llm_error_aux', 'llm_invalid_aux'):
                     next_title, llm_status, raw_preview = _generate_llm_session_title_for_agent(agent, user_text, assistant_text)
             source = llm_status
@@ -4831,9 +4853,9 @@ def _run_background_title_refresh(session_id: str, user_text: str, assistant_tex
             if agent and not aux_title_configured:
                 next_title, llm_status, raw_preview = _generate_llm_session_title_for_agent(agent, user_text, assistant_text)
                 if not next_title and llm_status in ('llm_error', 'llm_invalid'):
-                    next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent, use_agent_model=True)
+                    next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent, use_agent_model=True, conversation_id=session_id)
             else:
-                next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text)
+                next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, conversation_id=session_id)
                 if not next_title and agent and llm_status in ('llm_error_aux', 'llm_invalid_aux'):
                     next_title, llm_status, raw_preview = _generate_llm_session_title_for_agent(agent, user_text, assistant_text)
         if not next_title:
@@ -4896,7 +4918,7 @@ def generate_session_title_for_session(session, *, prefer_latest: bool = False,
     with profiles_api.profile_env_for_background_worker(session, "manual title regeneration", logger_override=logger):
         if not _aux_title_generation_enabled():
             return None, 'title_generation_disabled', ''
-        next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent)
+        next_title, llm_status, raw_preview = _generate_llm_session_title_via_aux(user_text, assistant_text, agent=agent, conversation_id=getattr(session, 'session_id', '') or '')
     if next_title:
         return next_title, llm_status, raw_preview
     fallback_title = _fallback_title_from_exchange(user_text, assistant_text)