diff --git a/plugins/platforms/buzz/adapter.py b/plugins/platforms/buzz/adapter.py
index b07830ae9b6e..4ba989bb5cca 100644
--- a/plugins/platforms/buzz/adapter.py
+++ b/plugins/platforms/buzz/adapter.py
@@ -803,6 +803,7 @@ async def _handle_membership_event(self, websocket, subscriptions: Dict[str, Opt
         subscribe to any new ones (fresh DMs dispatch from their beginning)."""
         self._membership_since = max(self._membership_since, int(event.get("created_at") or 0))
         before = set(self._channel_state)
+        await self._discover_joined_channels()
         await self._discover_dms(seed=False)
         for channel_id in self._channel_state:
             if channel_id in before:
@@ -962,6 +963,32 @@ async def _discover_dms(self, *, seed: bool) -> None:
             else:
                 self._channel_state[ch_id] = {"chat_type": "group", "last_ts": 0, "seen": OrderedDict()}
 
+    async def _discover_joined_channels(self) -> None:
+        """Adopt newly joined community channels when no watch list is pinned.
+
+        The initial high-water mark suppresses pre-membership history, matching
+        startup channel discovery. This is deliberately separate from the DM
+        fallback: real channels must never be reclassified as DMs merely
+        because their membership changes.
+        """
+        if self.channels:
+            return
+        code, out, err = await self._run_cli(["channels", "list"])
+        if code != 0:
+            logger.debug(
+                "Buzz: could not discover newly joined channels — %s", _cli_error_message(err, code)
+            )
+            return
+        for ch in _parse_json_list(out):
+            ch_id = str(ch.get("channel_id") or "")
+            if not ch_id:
+                continue
+            self._channel_meta[ch_id] = ch
+            self._channel_names.setdefault(ch_id, str(ch.get("name") or ch_id))
+            if ch_id in self._channel_state or self._may_reclassify_as_dm(ch_id):
+                continue
+            await self._seed_channel(ch_id, chat_type="group")
+
     async def _poll_channel(self, channel_id: str) -> None:
         state = self._channel_state.get(channel_id)
         if state is None:
diff --git a/tests/gateway/test_buzz_websocket.py b/tests/gateway/test_buzz_websocket.py
index d6762fb9a74f..fc5c818f28ba 100644
--- a/tests/gateway/test_buzz_websocket.py
+++ b/tests/gateway/test_buzz_websocket.py
@@ -119,3 +119,83 @@ async def recv(self):
         await adapter._authenticate_websocket(RejectingWs())
 
 
+
+@pytest.mark.asyncio
+async def test_membership_event_adopts_new_named_channel_when_unpinned():
+    """A new community membership must subscribe without a gateway restart (#75107)."""
+    adapter = _make_adapter()
+    new_channel = "new-community-channel"
+
+    messages_get_calls = 0
+
+    async def run_cli(args, **_kwargs):
+        nonlocal messages_get_calls
+        if args == ["dms", "list"]:
+            return 0, json.dumps([{"dm_id": new_channel}]), ""
+        if args == ["channels", "list"]:
+            return 0, json.dumps([
+                {"channel_id": new_channel, "name": "release-team", "description": "Announcements"}
+            ]), ""
+        if args[:2] == ["messages", "get"]:
+            messages_get_calls += 1
+            return 0, json.dumps([{"id": "pre-join", "created_at": 41}]), ""
+        raise AssertionError(f"unexpected CLI command: {args}")
+
+    class WebSocket:
+        def __init__(self):
+            self.sent = []
+
+        async def send(self, raw):
+            self.sent.append(json.loads(raw))
+
+    adapter._run_cli = run_cli
+    websocket = WebSocket()
+    subscriptions = {"membership": None}
+    await adapter._handle_membership_event(websocket, subscriptions, {"created_at": 42})
+
+    state = adapter._channel_state[new_channel]
+    assert state["chat_type"] == "group"
+    assert state["last_ts"] == 41
+    assert "pre-join" in state["seen"]
+    subscription_id = next(key for key, value in subscriptions.items() if value == new_channel)
+    assert websocket.sent == [[
+        "REQ", subscription_id, {"kinds": [9], "#h": [new_channel], "since": 40}
+    ]]
+
+    await adapter._handle_membership_event(websocket, subscriptions, {"created_at": 43})
+    assert messages_get_calls == 1
+    assert len(websocket.sent) == 1
+
+@pytest.mark.asyncio
+async def test_membership_event_does_not_adopt_channel_outside_explicit_watch_list():
+    adapter = _make_adapter({"channels": [CHANNEL]})
+
+    async def run_cli(args, **_kwargs):
+        if args == ["dms", "list"]:
+            return 0, "[]", ""
+        if args == ["channels", "list"]:
+            return 0, json.dumps([
+                {"channel_id": "not-configured", "name": "release-team", "description": "Announcements"}
+            ]), ""
+        raise AssertionError(f"unexpected CLI command: {args}")
+
+    adapter._run_cli = run_cli
+    await adapter._handle_membership_event(_FakeWebSocket(), {"membership": None}, {"created_at": 42})
+    assert "not-configured" not in adapter._channel_state
+
+@pytest.mark.asyncio
+async def test_membership_event_leaves_state_unchanged_when_channel_lookup_fails():
+    adapter = _make_adapter()
+
+    async def run_cli(args, **_kwargs):
+        if args == ["dms", "list"]:
+            return 0, "[]", ""
+        if args == ["channels", "list"]:
+            return 1, "", "unavailable"
+        raise AssertionError(f"unexpected CLI command: {args}")
+
+    adapter._run_cli = run_cli
+    subscriptions = {"membership": None}
+    await adapter._handle_membership_event(_FakeWebSocket(), subscriptions, {"created_at": 42})
+    assert adapter._channel_state == {}
+    assert subscriptions == {"membership": None}