fix(slack): edit status bubbles in place instead of posting new ones

Progress/status callbacks (context-pressure, compression retries,
model fallback) route through _send_or_update_status_coro, which
edits the previous bubble for the same status_key when the adapter
implements send_or_update_status — but only Telegram did. On Slack
every status event posted a fresh thread message, so a compression
retry loop spammed a dozen out-of-order bubbles into the thread
('Context too large 1/3... 2/3... 3/3', fallback switches, etc.).

Implement send_or_update_status on the Slack adapter following the
Telegram pattern (#30045): first call posts and caches the message ts
per (channel, thread, status_key); subsequent calls edit that message
via chat.update. Edit failure drops the cached ts and falls back to a
fresh send. Cache is FIFO-bounded.

tests/gateway/test_slack_status_update.py

@@ -0,0 +1,144 @@
+"""Tests for SlackAdapter.send_or_update_status (issue #30045, Slack).
+
+The status-update path must:
+  1. Send a fresh message on the first call for a (channel, thread, key).
+  2. Edit that same message on subsequent calls with the same key.
+  3. Fall back to sending fresh when the cached message edit fails.
+  4. Keep distinct keys and distinct threads independent.
+"""
+
+from __future__ import annotations
+
+import sys
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+
+def _ensure_slack_mock():
+    if "slack_bolt" in sys.modules and hasattr(sys.modules["slack_bolt"], "__file__"):
+        return
+    slack_bolt = MagicMock()
+    slack_bolt.async_app.AsyncApp = MagicMock
+    slack_bolt.adapter.socket_mode.async_handler.AsyncSocketModeHandler = MagicMock
+    slack_sdk = MagicMock()
+    slack_sdk.web.async_client.AsyncWebClient = MagicMock
+    for name, mod in [
+        ("slack_bolt", slack_bolt),
+        ("slack_bolt.async_app", slack_bolt.async_app),
+        ("slack_bolt.adapter", slack_bolt.adapter),
+        ("slack_bolt.adapter.socket_mode", slack_bolt.adapter.socket_mode),
+        (
+            "slack_bolt.adapter.socket_mode.async_handler",
+            slack_bolt.adapter.socket_mode.async_handler,
+        ),
+        ("slack_sdk", slack_sdk),
+        ("slack_sdk.web", slack_sdk.web),
+        ("slack_sdk.web.async_client", slack_sdk.web.async_client),
+    ]:
+        sys.modules.setdefault(name, mod)
+    sys.modules.setdefault("aiohttp", MagicMock())
+
+
+_ensure_slack_mock()
+
+import plugins.platforms.slack.adapter as _slack_mod  # noqa: E402
+
+_slack_mod.SLACK_AVAILABLE = True
+
+from gateway.config import PlatformConfig  # noqa: E402
+from plugins.platforms.slack.adapter import SlackAdapter  # noqa: E402
+
+
+@pytest.fixture()
+def adapter():
+    config = PlatformConfig(enabled=True, token="***")
+    a = SlackAdapter(config)
+    a._app = MagicMock()
+    client = AsyncMock()
+    client.chat_postMessage = AsyncMock(
+        side_effect=lambda **kw: {"ok": True, "ts": f"ts_{client.chat_postMessage.call_count}"}
+    )
+    client.chat_update = AsyncMock(return_value={"ok": True})
+    a._get_client = MagicMock(return_value=client)
+    a._bot_user_id = "U_BOT"
+    a._running = True
+    a.stop_typing = AsyncMock()
+    return a
+
+
+METADATA = {"thread_id": "1784585355.415219"}
+
+
+@pytest.mark.asyncio
+async def test_first_call_sends_fresh(adapter):
+    result = await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 1/3", metadata=METADATA
+    )
+    assert result.success
+    client = adapter._get_client.return_value
+    assert client.chat_postMessage.call_count == 1
+    assert client.chat_update.call_count == 0
+
+
+@pytest.mark.asyncio
+async def test_second_call_edits_same_message(adapter):
+    r1 = await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 1/3", metadata=METADATA
+    )
+    r2 = await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 2/3", metadata=METADATA
+    )
+    assert r1.success and r2.success
+    client = adapter._get_client.return_value
+    assert client.chat_postMessage.call_count == 1
+    assert client.chat_update.call_count == 1
+    # The edit must target the ts of the first send.
+    assert client.chat_update.call_args.kwargs["ts"] == r1.message_id
+
+
+@pytest.mark.asyncio
+async def test_edit_failure_falls_back_to_fresh_send(adapter):
+    await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 1/3", metadata=METADATA
+    )
+    client = adapter._get_client.return_value
+    client.chat_update = AsyncMock(side_effect=RuntimeError("message_not_found"))
+    r2 = await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 2/3", metadata=METADATA
+    )
+    assert r2.success
+    assert client.chat_postMessage.call_count == 2
+    # Cached id was replaced: a third call edits the NEW message.
+    client.chat_update = AsyncMock(return_value={"ok": True})
+    r3 = await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing 3/3", metadata=METADATA
+    )
+    assert r3.success
+    assert client.chat_update.call_args.kwargs["ts"] == r2.message_id
+
+
+@pytest.mark.asyncio
+async def test_distinct_keys_do_not_crosstalk(adapter):
+    await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing", metadata=METADATA
+    )
+    await adapter.send_or_update_status(
+        "C_CHAN", "model_fallback", "falling back", metadata=METADATA
+    )
+    client = adapter._get_client.return_value
+    assert client.chat_postMessage.call_count == 2
+    assert client.chat_update.call_count == 0
+
+
+@pytest.mark.asyncio
+async def test_distinct_threads_do_not_crosstalk(adapter):
+    await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing", metadata={"thread_id": "111.1"}
+    )
+    await adapter.send_or_update_status(
+        "C_CHAN", "context_pressure", "compressing", metadata={"thread_id": "222.2"}
+    )
+    client = adapter._get_client.return_value
+    assert client.chat_postMessage.call_count == 2
+    assert client.chat_update.call_count == 0