feat: thread_has_agent_participation + ACK reply linkage

1. thread_has_agent_participation (SOWA Priority 11):
   - New function has_agent_chat_participation() in behavior_policy.py
   - Checks if agent responded to ANY user in this chat within 30min
   - When active + user asks question/imperative → agent responds
   - Different from per-user conversation_context (Priority 12)
   - Wired into both detect_explicit_request() and analyze_message()

2. ACK reply_to_message_id:
   - When SOWA sends ACK ("NUTRA тут"), it now replies to the user's
     message instead of sending a standalone message
   - Better UX: visually linked to what the user wrote
   - Uses allow_sending_without_reply=True for safety

Known issue (not fixed - too risky):
- Lines 1368-1639 in http_api.py are dead code (brand commands /бренд)
  at incorrect indentation level (8 spaces, inside unreachable block)
- These commands never worked on NODE1, fixing 260 lines of indentation
  carries regression risk — deferred to separate cleanup PR

Co-authored-by: Cursor <cursoragent@cursor.com>

gateway-bot/http_api.py

@@ -41,6 +41,7 @@ from behavior_policy import (
     record_ack,
     get_ack_text,
     is_prober_request,
+    has_agent_chat_participation,
     NO_OUTPUT,
     BehaviorDecision,
     AGENT_NAME_VARIANTS,
@@ -2026,6 +2027,9 @@ async def handle_telegram_webhook(
                     mentioned_agents.append(aid)
                     break
     
+    # Gateway: check if agent has been active in this chat recently (any user)
+    agent_active_in_chat = has_agent_chat_participation(agent_config.agent_id, chat_id)
+    
     # Gateway: compute has_explicit_request (single source of truth)
     # CONTRACT: imperative OR (? AND (dm OR reply OR mention OR thread))
     has_explicit_request = detect_explicit_request(
@@ -2033,7 +2037,7 @@ async def handle_telegram_webhook(
         is_dm=is_private_chat,
         is_reply_to_agent=is_reply_to_agent,
         mentioned_agents=mentioned_agents,
-        thread_has_agent_participation=False,  # REQUIRED, fail-closed default
+        thread_has_agent_participation=agent_active_in_chat,
     )
     
     # Check if this is a prober request (chat_id=0 or user_id=0)
@@ -2051,7 +2055,7 @@ async def handle_telegram_webhook(
         payload_explicit_request=has_explicit_request,
         payload_has_link=has_link,
         is_reply_to_agent=is_reply_to_agent,
-        thread_has_agent_participation=False,  # TODO: track per thread
+        thread_has_agent_participation=agent_active_in_chat,
     )
     respond_decision = sowa_decision.should_respond
     respond_reason = sowa_decision.reason
@@ -2088,10 +2092,16 @@ async def handle_telegram_webhook(
                 try:
                     url = f"https://api.telegram.org/bot{token}/sendMessage"
                     async with httpx.AsyncClient(timeout=30) as client:
-                        resp = await client.post(url, json={
+                        ack_payload = {
                             "chat_id": chat_id,
                             "text": ack_text,
-                        })
+                        }
+                        # Link ACK to the user's message for better UX
+                        msg_id = update.message.get("message_id")
+                        if msg_id:
+                            ack_payload["reply_to_message_id"] = msg_id
+                            ack_payload["allow_sending_without_reply"] = True
+                        resp = await client.post(url, json=ack_payload)
                         if resp.status_code == 200:
                             logger.info(f"\U0001f44b ACK sent to chat {chat_id}: {ack_text}")
                         else: