diff --git a/slack-app-manifest.yaml b/slack-app-manifest.yaml
index 40ecb8dd..67427d8a 100644
--- a/slack-app-manifest.yaml
+++ b/slack-app-manifest.yaml
@@ -33,6 +33,10 @@ oauth_config:
       - users:read.email
   pkce_enabled: false
 settings:
+  event_subscriptions:
+    bot_events:
+      - message.channels
+      - message.groups
   interactivity:
     is_enabled: true
   org_deploy_enabled: false
diff --git a/src/firetower/slack_app/bolt.py b/src/firetower/slack_app/bolt.py
index b0c9c699..d9466876 100644
--- a/src/firetower/slack_app/bolt.py
+++ b/src/firetower/slack_app/bolt.py
@@ -47,6 +47,7 @@
     handle_statuspage_submission,
 )
 from firetower.slack_app.handlers.subject import handle_subject_command
+from firetower.slack_app.handlers.topic_guard import handle_channel_topic_change
 from firetower.slack_app.handlers.update_incident import (
     handle_update_command,
     handle_update_incident_submission,
@@ -108,6 +109,7 @@ def get_bolt_app() -> App:
         _bolt_app.command("/inc")(handle_command)
         _bolt_app.command("/testinc")(handle_command)
         _register_views(_bolt_app)
+        _register_event_handlers(_bolt_app)
     return _bolt_app
 
 
@@ -213,6 +215,33 @@ def wrapper(*args: Any, **kwargs: Any) -> Any:
     return decorator
 
 
+def _with_event_metrics(event_type: str) -> Callable[..., Callable[..., Any]]:
+    """Wrap a Bolt event handler to emit submitted/completed/failed metrics.
+
+    Uses a ``slack_app.events`` namespace so event volume does not pollute the
+    ``slack_app.views`` dashboards.
+    """
+
+    def decorator(func: Callable[..., Any]) -> Callable[..., Any]:
+        @wraps(func)
+        def wrapper(*args: Any, **kwargs: Any) -> Any:
+            close_old_connections()
+            tags = [f"event_type:{event_type}"]
+            statsd.increment("slack_app.events.submitted", tags=tags)
+            try:
+                result = func(*args, **kwargs)
+                statsd.increment("slack_app.events.completed", tags=tags)
+                return result
+            except Exception:
+                logger.exception("Event handler failed: %s", event_type)
+                statsd.increment("slack_app.events.failed", tags=tags)
+                raise
+
+        return wrapper
+
+    return decorator
+
+
 def _register_views(app: App) -> None:
     """Register view handlers (modals, etc.) on the Bolt app."""
     app.view("backfill_incident_modal")(
@@ -256,3 +285,23 @@ def _register_views(app: App) -> None:
         "affected_region_tags",
     ):
         app.options(action_id)(handle_tag_options)
+
+
+def _ignore_message_event(ack: Any) -> None:
+    """No-op catch-all for message events.
+
+    Subscribing to message.channels/message.groups opts the bot into the full
+    message firehose. Without a catch-all listener Bolt logs an "Unhandled
+    request" warning for every non-topic message. This listener is registered
+    after the channel_topic handler, so for topic changes the specific handler
+    runs first and returns before this one is reached.
+    """
+    ack()
+
+
+def _register_event_handlers(app: App) -> None:
+    """Register Slack event subscriptions on the Bolt app."""
+    app.event({"type": "message", "subtype": "channel_topic"})(
+        _with_event_metrics("channel_topic")(handle_channel_topic_change)
+    )
+    app.event("message")(_ignore_message_event)
diff --git a/src/firetower/slack_app/handlers/topic_guard.py b/src/firetower/slack_app/handlers/topic_guard.py
new file mode 100644
index 00000000..b1533250
--- /dev/null
+++ b/src/firetower/slack_app/handlers/topic_guard.py
@@ -0,0 +1,114 @@
+import logging
+import threading
+from collections import OrderedDict
+from typing import Any
+
+from firetower.incidents.hooks import build_channel_topic
+from firetower.integrations.services.slack import SlackService, escape_slack_text
+from firetower.slack_app.handlers.utils import get_incident_from_channel
+
+logger = logging.getLogger(__name__)
+
+_slack_service = SlackService()
+
+_bot_user_id: str | None = None
+
+# Bounded set of recently handled channel_topic event ids, used to drop Slack
+# redeliveries. Socket Mode strips the X-Slack-Retry-Num header (it lives on the
+# envelope, not the event payload Bolt forwards), so we dedup on the event's own
+# id/timestamp instead. This in-memory cache is per-process, so it only dedups
+# correctly while the firetower-slack-app Cloud Run service stays single-instance
+# (max_instance_count = 1); scaling it out would split the cache across replicas.
+_RECENT_EVENT_CACHE_SIZE = 256
+_recent_event_ids: "OrderedDict[str, None]" = OrderedDict()
+# Bolt dispatches event listeners on a thread pool, so guard the cache against
+# concurrent check-then-set/evict races.
+_recent_event_ids_lock = threading.Lock()
+
+
+def _get_bot_user_id(client: Any) -> str | None:
+    """Return the bot's own Slack user id, caching it after the first lookup."""
+    global _bot_user_id  # noqa: PLW0603
+    if _bot_user_id is None:
+        try:
+            _bot_user_id = client.auth_test()["user_id"]
+        except Exception:
+            logger.exception("auth_test failed while resolving bot user id")
+            return None
+    return _bot_user_id
+
+
+def _event_id(event: dict) -> str | None:
+    return event.get("event_ts") or event.get("ts")
+
+
+def _seen_recently(event_id: str) -> bool:
+    """Return True if this event id was already handled, recording it otherwise."""
+    with _recent_event_ids_lock:
+        if event_id in _recent_event_ids:
+            return True
+        _recent_event_ids[event_id] = None
+        while len(_recent_event_ids) > _RECENT_EVENT_CACHE_SIZE:
+            _recent_event_ids.popitem(last=False)
+        return False
+
+
+def _build_reset_message(attempted: str) -> str:
+    lines = [
+        "Channel topics here are managed by Firetower and reflect the incident's "
+        "current status, so I reset it.",
+    ]
+    if attempted:
+        quoted = "\n".join(
+            f"> {escape_slack_text(line)}" for line in attempted.splitlines()
+        )
+        lines.append(f"You tried to set:\n{quoted}")
+    lines.append(
+        "To change incident details (which update the topic automatically), use "
+        "`/ft subject <title>`, `/ft severity <P0-P4>`, or `/ft captain`."
+    )
+    return "\n\n".join(lines)
+
+
+def handle_channel_topic_change(event: dict, client: Any) -> None:
+    """Reset manual incident-channel topic edits and nudge the editor.
+
+    Slack emits a ``channel_topic`` message event whenever a channel's topic
+    changes, including when Firetower sets it. The bot-author guard prevents an
+    infinite reset loop on our own edits, and the event-id dedup guard prevents a
+    second reset and ephemeral when Slack redelivers the event.
+    """
+    if event.get("user") == _get_bot_user_id(client):
+        return
+
+    channel_id = event.get("channel")
+    if not channel_id:
+        return
+
+    event_id = _event_id(event)
+    if event_id is not None and _seen_recently(event_id):
+        logger.info("Skipping duplicate channel_topic event for channel %s", channel_id)
+        return
+
+    incident = get_incident_from_channel(channel_id)
+    if incident is None:
+        return
+
+    canonical = build_channel_topic(incident)
+    attempted = event.get("topic", "")
+
+    logger.info(
+        "Resetting manual topic change in incident channel %s (incident %s)",
+        channel_id,
+        incident.incident_number,
+    )
+    _slack_service.set_channel_topic(channel_id, canonical)
+
+    try:
+        client.chat_postEphemeral(
+            channel=channel_id,
+            user=event.get("user"),
+            text=_build_reset_message(attempted),
+        )
+    except Exception:
+        logger.exception("Failed to post topic-reset ephemeral to %s", channel_id)
diff --git a/src/firetower/slack_app/tests/test_topic_guard.py b/src/firetower/slack_app/tests/test_topic_guard.py
new file mode 100644
index 00000000..b752a2dc
--- /dev/null
+++ b/src/firetower/slack_app/tests/test_topic_guard.py
@@ -0,0 +1,177 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from firetower.slack_app.handlers import topic_guard
+from firetower.slack_app.handlers.topic_guard import handle_channel_topic_change
+
+CHANNEL_ID = "C_TEST_CHANNEL"
+BOT_USER_ID = "U0000"
+CANONICAL = "[P2] <https://ft/INC-1|INC-1 Test>"
+
+
+@pytest.fixture(autouse=True)
+def reset_module_state():
+    topic_guard._bot_user_id = None
+    topic_guard._recent_event_ids.clear()
+    yield
+    topic_guard._bot_user_id = None
+    topic_guard._recent_event_ids.clear()
+
+
+@pytest.fixture
+def client():
+    c = MagicMock()
+    c.auth_test.return_value = {"user_id": BOT_USER_ID}
+    return c
+
+
+_TS_COUNTER = [0]
+
+
+def _event(user="U_OTHER", topic="Something custom", channel=CHANNEL_ID, ts=None):
+    if ts is None:
+        _TS_COUNTER[0] += 1
+        ts = f"1700000000.{_TS_COUNTER[0]:06d}"
+    return {
+        "type": "message",
+        "subtype": "channel_topic",
+        "channel": channel,
+        "user": user,
+        "topic": topic,
+        "event_ts": ts,
+    }
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.build_channel_topic")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_manual_change_resets_and_notifies(
+    mock_get_incident, mock_build_topic, mock_slack_service, client
+):
+    mock_get_incident.return_value = MagicMock()
+    mock_build_topic.return_value = CANONICAL
+
+    handle_channel_topic_change(_event(topic="My custom topic"), client)
+
+    mock_slack_service.set_channel_topic.assert_called_once_with(CHANNEL_ID, CANONICAL)
+    client.chat_postEphemeral.assert_called_once()
+    kwargs = client.chat_postEphemeral.call_args[1]
+    assert kwargs["channel"] == CHANNEL_ID
+    assert kwargs["user"] == "U_OTHER"
+    assert "My custom topic" in kwargs["text"]
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_bot_authored_event_is_ignored(mock_get_incident, mock_slack_service, client):
+    handle_channel_topic_change(_event(user=BOT_USER_ID), client)
+
+    mock_get_incident.assert_not_called()
+    mock_slack_service.set_channel_topic.assert_not_called()
+    client.chat_postEphemeral.assert_not_called()
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_non_incident_channel_is_noop(mock_get_incident, mock_slack_service, client):
+    mock_get_incident.return_value = None
+
+    handle_channel_topic_change(_event(), client)
+
+    mock_slack_service.set_channel_topic.assert_not_called()
+    client.chat_postEphemeral.assert_not_called()
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_missing_channel_is_noop(mock_get_incident, mock_slack_service, client):
+    event = _event()
+    del event["channel"]
+
+    handle_channel_topic_change(event, client)
+
+    mock_get_incident.assert_not_called()
+    mock_slack_service.set_channel_topic.assert_not_called()
+    client.chat_postEphemeral.assert_not_called()
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.build_channel_topic")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_attempted_topic_is_escaped(
+    mock_get_incident, mock_build_topic, mock_slack_service, client
+):
+    mock_get_incident.return_value = MagicMock()
+    mock_build_topic.return_value = CANONICAL
+
+    handle_channel_topic_change(
+        _event(topic="<!channel> see <https://evil|here> & <@U999>"), client
+    )
+
+    text = client.chat_postEphemeral.call_args[1]["text"]
+    assert "<!channel>" not in text
+    assert "<@U999>" not in text
+    assert "<https://evil|here>" not in text
+    assert "&lt;!channel&gt;" in text
+    assert "&amp;" in text
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.build_channel_topic")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_ephemeral_failure_still_resets(
+    mock_get_incident, mock_build_topic, mock_slack_service, client
+):
+    mock_get_incident.return_value = MagicMock()
+    mock_build_topic.return_value = CANONICAL
+    client.chat_postEphemeral.side_effect = Exception("boom")
+
+    handle_channel_topic_change(_event(), client)
+
+    mock_slack_service.set_channel_topic.assert_called_once_with(CHANNEL_ID, CANONICAL)
+    client.chat_postEphemeral.assert_called_once()
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.build_channel_topic")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_bot_id_cache_is_reused(
+    mock_get_incident, mock_build_topic, mock_slack_service, client
+):
+    mock_get_incident.return_value = MagicMock()
+    mock_build_topic.return_value = CANONICAL
+
+    handle_channel_topic_change(_event(), client)
+    handle_channel_topic_change(_event(), client)
+
+    assert client.auth_test.call_count == 1
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_auth_test_failure_does_not_crash(
+    mock_get_incident, mock_slack_service, client
+):
+    client.auth_test.side_effect = Exception("transient")
+
+    handle_channel_topic_change(_event(), client)
+
+    mock_get_incident.assert_called_once()
+
+
+@patch("firetower.slack_app.handlers.topic_guard._slack_service")
+@patch("firetower.slack_app.handlers.topic_guard.build_channel_topic")
+@patch("firetower.slack_app.handlers.topic_guard.get_incident_from_channel")
+def test_duplicate_event_id_is_skipped(
+    mock_get_incident, mock_build_topic, mock_slack_service, client
+):
+    mock_get_incident.return_value = MagicMock()
+    mock_build_topic.return_value = CANONICAL
+    event = _event(ts="1700000000.999999")
+
+    handle_channel_topic_change(event, client)
+    handle_channel_topic_change(event, client)
+
+    mock_slack_service.set_channel_topic.assert_called_once()
+    client.chat_postEphemeral.assert_called_once()