diff --git a/gateway-bot/behavior_policy.py b/gateway-bot/behavior_policy.py
index ddf52f83..3c4636a7 100644
--- a/gateway-bot/behavior_policy.py
+++ b/gateway-bot/behavior_policy.py
@@ -118,6 +118,24 @@ def has_recent_interaction(agent_id: str, chat_id: str, user_id: str) -> bool:
     return is_recent
 
 
+def has_agent_chat_participation(agent_id: str, chat_id: str) -> bool:
+    """
+    Check if agent has responded to ANY user in this chat recently.
+    Used for thread_has_agent_participation (SOWA Priority 11).
+    
+    Different from has_recent_interaction():
+    - has_recent_interaction: THIS user talked to agent (per-user)
+    - has_agent_chat_participation: agent talked to ANYONE in this chat (per-chat)
+    """
+    now = time.time()
+    str_chat_id = str(chat_id)
+    for (aid, cid, _uid), timestamp in _conversation_context.items():
+        if aid == agent_id and cid == str_chat_id:
+            if now - timestamp < CONVERSATION_CONTEXT_TIMEOUT:
+                return True
+    return False
+
+
 def cleanup_old_contexts() -> None:
     """Remove old conversation contexts and ACK cooldowns to prevent memory leak."""
     global _conversation_context, _ack_cooldown
diff --git a/gateway-bot/http_api.py b/gateway-bot/http_api.py
index d5e320da..4c20a92d 100644
--- a/gateway-bot/http_api.py
+++ b/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: