fix(scheduler): inject delivered output into receiver session with sliding window

Further refinements on top of #2795:

- persist real session_id (notify_session_id) at task creation so group chats
  correctly map back to the user's actual conversation
- mark scheduler turns with [SCHEDULED] (recognise legacy "Scheduled task"
  prefix too for backward-compatible pruning)
- prune both DB and in-memory to scheduler_inject_max_per_session (default 3),
  only marker-tagged pairs are touched; regular user turns never deleted
- send_message type gated by scheduler_inject_send_message (default false) —
  fixed reminder text rarely benefits follow-up Q&A

Co-authored-by: huangrichao2020 <grdomai43881@gmail.com>

agent/tools/scheduler/integration.py

@@ -95,10 +95,24 @@ def _remember_delivered_output(
     Uses notify_session_id (the real chat session_id stored at task creation time)
     so that group chats correctly associate the output with the user's conversation.
     Falls back to receiver for backward compatibility with old tasks.
+
+    Per-action-type behaviour:
+        - agent_task / tool_call / skill_call: gated by ``scheduler_inject_to_session``
+          (default True). These produce AI-generated content worth remembering.
+        - send_message: additionally gated by ``scheduler_inject_send_message``
+          (default False). Fixed reminder text rarely benefits follow-up Q&A and
+          would just consume context tokens.
     """
     if not content:
         return
     action = task.get("action", {})
+    action_type = action.get("type", "")
+
+    # send_message defaults to NOT being injected; explicit opt-in via config.
+    if action_type == "send_message":
+        if not conf().get("scheduler_inject_send_message", False):
+            return
+
     session_id = action.get("notify_session_id") or action.get("receiver")
     if not session_id:
         return