fix(slack): evict oldest tracked thread timestamps

plugins/platforms/slack/adapter.py

@@ -742,11 +742,11 @@ class SlackAdapter(BasePlatformAdapter):
         self._clarify_resolved: Dict[str, bool] = {}
         # Track timestamps of messages sent by the bot so we can respond
         # to thread replies even without an explicit @mention.
-        self._bot_message_ts: set = set()
+        self._bot_message_ts: set[str] = set()
         self._BOT_TS_MAX = 5000  # cap to avoid unbounded growth
         # Track threads where the bot has been @mentioned — once mentioned,
         # respond to ALL subsequent messages in that thread automatically.
-        self._mentioned_threads: set = set()
+        self._mentioned_threads: set[str] = set()
         self._MENTIONED_THREADS_MAX = 5000
         # Assistant thread metadata keyed by (team_id, channel_id, thread_ts).
         # Slack's AI Assistant lifecycle events can arrive before/alongside
@@ -827,6 +827,43 @@ class SlackAdapter(BasePlatformAdapter):
                     await result
                 break
 
+    @staticmethod
+    def _slack_timestamp_sort_key(ts: str) -> Tuple[int, int, str]:
+        """Return a chronological, deterministic sort key for Slack timestamps."""
+        seconds, _, fraction = str(ts).partition(".")
+        try:
+            seconds_int = int(seconds)
+        except ValueError:
+            seconds_int = 0
+        try:
+            fraction_int = int((fraction + "000000")[:6] or "0")
+        except ValueError:
+            fraction_int = 0
+        return seconds_int, fraction_int, str(ts)
+
+    @classmethod
+    def _discard_oldest_slack_timestamps(
+        cls, timestamps: set[str], count: int
+    ) -> None:
+        """Discard the oldest Slack timestamps from a bounded tracking set."""
+        if count <= 0:
+            return
+        for old_ts in sorted(timestamps, key=cls._slack_timestamp_sort_key)[:count]:
+            timestamps.discard(old_ts)
+
+    def _trim_bot_message_timestamps(self) -> None:
+        if len(self._bot_message_ts) <= self._BOT_TS_MAX:
+            return
+        excess = len(self._bot_message_ts) - self._BOT_TS_MAX // 2
+        self._discard_oldest_slack_timestamps(self._bot_message_ts, excess)
+
+    def _trim_mentioned_threads(self) -> None:
+        if len(self._mentioned_threads) <= self._MENTIONED_THREADS_MAX:
+            return
+        self._discard_oldest_slack_timestamps(
+            self._mentioned_threads, self._MENTIONED_THREADS_MAX // 2
+        )
+
     def _start_socket_mode_handler(self) -> None:
         """Start the Slack Socket Mode background task."""
         if not self._app or not self._app_token:
@@ -2002,10 +2039,7 @@ class SlackAdapter(BasePlatformAdapter):
                 # Also register the thread root so replies-to-my-replies work
                 if thread_ts:
                     self._bot_message_ts.add(thread_ts)
-                if len(self._bot_message_ts) > self._BOT_TS_MAX:
-                    excess = len(self._bot_message_ts) - self._BOT_TS_MAX // 2
-                    for old_ts in list(self._bot_message_ts)[:excess]:
-                        self._bot_message_ts.discard(old_ts)
+                self._trim_bot_message_timestamps()
 
             return SendResult(
                 success=True,
@@ -2545,10 +2579,7 @@ class SlackAdapter(BasePlatformAdapter):
         if not thread_ts:
             return
         self._bot_message_ts.add(thread_ts)
-        if len(self._bot_message_ts) > self._BOT_TS_MAX:
-            excess = len(self._bot_message_ts) - self._BOT_TS_MAX // 2
-            for old_ts in list(self._bot_message_ts)[:excess]:
-                self._bot_message_ts.discard(old_ts)
+        self._trim_bot_message_timestamps()
 
     def _is_retryable_upload_error(self, exc: Exception) -> bool:
         """Best-effort detection for transient Slack upload failures."""
@@ -3772,12 +3803,7 @@ class SlackAdapter(BasePlatformAdapter):
         if not thread_ts:
             return
         self._mentioned_threads.add(thread_ts)
-        if len(self._mentioned_threads) > self._MENTIONED_THREADS_MAX:
-            to_remove = list(self._mentioned_threads)[
-                : self._MENTIONED_THREADS_MAX // 2
-            ]
-            for t in to_remove:
-                self._mentioned_threads.discard(t)
+        self._trim_mentioned_threads()
 
     async def _bot_authored_thread_root(
         self, channel_id: str, thread_ts: str, team_id: str = ""