feat(telegram): send fresh finals for stale preview streams (port openclaw#72038) (#16261)

Ports openclaw/openclaw#72038 to hermes-agent.

Telegram's `editMessageText` preserves the original message timestamp,
so a long-running streamed reply (reasoning models that take 60+ seconds
to finish) would keep the first-token timestamp even after completion.
Users can't tell how long a task actually took.

When a preview message has been visible for >= 60s (configurable via
`streaming.fresh_final_after_seconds`), finalize by sending a fresh
message instead of editing in place, then best-effort delete the stale
preview. Short previews still edit in place (the existing fast path).

Implementation notes adapted from OpenClaw's TypeScript original:
- `StreamConsumerConfig` gains `fresh_final_after_seconds` (default 0 =
  legacy edit-in-place). Gateway-level `StreamingConfig` defaults to 60.
- `GatewayStreamConsumer` tracks `_message_created_ts` at first-send and
  checks it in `_send_or_edit` on `finalize=True`. New helpers
  `_should_send_fresh_final` + `_try_fresh_final`.
- `BasePlatformAdapter` gains optional `delete_message(chat_id, message_id)`
  returning False by default. `TelegramAdapter` implements it via
  `_bot.delete_message`.
- `gateway/run.py` only enables fresh-final for `Platform.TELEGRAM`;
  other platforms ignore the setting (they don't have the stale-edit
  timestamp problem or edit-then-read works cheaply).
- Fallback to normal edit on any fresh-send failure — no user-visible
  regression if Telegram rate-limits a send or the message is gone.

Tests: 15 new cases in tests/gateway/test_stream_consumer_fresh_final.py
covering short/long previews, config plumbing, delete-support absent,
send-failure fallback, __no_edit__ sentinel safety, and StreamingConfig
round-trip.

Co-authored-by: Hermes Agent <agent@nousresearch.com>

gateway/platforms/base.py

@@ -1258,6 +1258,27 @@ class BasePlatformAdapter(ABC):
         """
         return SendResult(success=False, error="Not supported")
 
+    async def delete_message(
+        self,
+        chat_id: str,
+        message_id: str,
+    ) -> bool:
+        """
+        Delete a previously sent message.  Optional — platforms that don't
+        support deletion return ``False`` and callers fall back to leaving
+        the message in place.
+
+        Used by the stream consumer's fresh-final cleanup path (see
+        openclaw/openclaw#72038) to remove long-lived preview messages
+        after sending the completed reply as a fresh message so the
+        platform's visible timestamp reflects completion time.
+
+        Returns ``True`` on successful deletion, ``False`` otherwise.
+        Subclasses should override for platforms with a deletion API
+        (e.g. Telegram ``deleteMessage``).
+        """
+        return False
+
     async def send_typing(self, chat_id: str, metadata=None) -> None:
         """
         Send a typing indicator.