fix(gateway): suppress duplicate replies on interrupt and streaming flood control

Three fixes for the duplicate reply bug affecting all gateway platforms:

1. base.py: Suppress stale response when the session was interrupted by a
   new message that hasn't been consumed yet. Checks both interrupt_event
   and _pending_messages to avoid false positives. (#8221, #2483)

2. run.py (return path): Remove response_previewed guard from already_sent
   check. Stream consumer's already_sent alone is authoritative — if
   content was delivered via streaming, the duplicate send must be
   suppressed regardless of the agent's response_previewed flag. (#8375)

3. run.py (queued-message path): Same fix — already_sent without
   response_previewed now correctly marks the first response as already
   streamed, preventing re-send before processing the queued message.

The response_previewed field is still produced by the agent (run_agent.py)
but is no longer required as a gate for duplicate suppression. The stream
consumer's already_sent flag is the delivery-level truth about what the
user actually saw.

Concepts from PR #8380 (konsisumer). Closes #8375, #8221, #2483.

gateway/platforms/base.py

@@ -1624,6 +1624,21 @@ class BasePlatformAdapter(ABC):
             # streaming already delivered the text (already_sent=True) or
             # when the message was queued behind an active agent.  Log at
             # DEBUG to avoid noisy warnings for expected behavior.
+            #
+            # Suppress stale response when the session was interrupted by a
+            # new message that hasn't been consumed yet.  The pending message
+            # is processed by the pending-message handler below (#8221/#2483).
+            if (
+                response
+                and interrupt_event.is_set()
+                and session_key in self._pending_messages
+            ):
+                logger.info(
+                    "[%s] Suppressing stale response for interrupted session %s",
+                    self.name,
+                    session_key,
+                )
+                response = None
             if not response:
                 logger.debug("[%s] Handler returned empty/None response for %s", self.name, event.source.chat_id)
             if response:

gateway/run.py

@@ -9231,15 +9231,11 @@ class GatewayRunner:
                                 pass
                         except Exception as e:
                             logger.debug("Stream consumer wait before queued message failed: %s", e)
-                    _response_previewed = bool(result.get("response_previewed"))
                     _already_streamed = bool(
                         _sc
                         and (
                             getattr(_sc, "final_response_sent", False)
-                            or (
-                                _response_previewed
-                                and getattr(_sc, "already_sent", False)
-                            )
+                            or getattr(_sc, "already_sent", False)
                         )
                     )
                     first_response = result.get("final_response", "")
@@ -9323,13 +9319,9 @@ class GatewayRunner:
         # them even if streaming had sent earlier partial output.
         _sc = stream_consumer_holder[0]
         if _sc and isinstance(response, dict) and not response.get("failed"):
-            _response_previewed = bool(response.get("response_previewed"))
             if (
                 getattr(_sc, "final_response_sent", False)
-                or (
-                    _response_previewed
-                    and getattr(_sc, "already_sent", False)
-                )
+                or getattr(_sc, "already_sent", False)
             ):
                 response["already_sent"] = True