fix: test DB isolation, Discord recovery, and over-mocked tests

Test data was bleeding into production tasks.db because
swarm.task_queue.models.DB_PATH (relative path) was never patched in
conftest.clean_database. Fixed by switching to absolute paths via
settings.repo_root and adding the missing module to the patching list.

Discord bot could leak orphaned clients on retry after ERROR state.
Added _cleanup_stale() to close stale client/task before each start()
attempt, with improved logging in the token watcher.

Rewrote test_paperclip_client.py to use httpx.MockTransport instead of
patching _get/_post/_delete — tests now exercise real HTTP status codes,
error handling, and JSON parsing. Added end-to-end test for
capture_error → create_task DB isolation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/integrations/test_discord_vendor.py

@@ -96,6 +96,42 @@ class TestDiscordVendor:
         await vendor.stop()
         assert vendor.state == PlatformState.DISCONNECTED
 
+    @pytest.mark.asyncio
+    async def test_cleanup_stale_closes_orphaned_client(self):
+        """_cleanup_stale should close any leftover client from a failed start."""
+        from integrations.chat_bridge.vendors.discord import DiscordVendor
+
+        vendor = DiscordVendor()
+        mock_client = MagicMock()
+        mock_client.is_closed.return_value = False
+        mock_client.close = AsyncMock()
+        vendor._client = mock_client
+
+        await vendor._cleanup_stale()
+        mock_client.close.assert_called_once()
+        assert vendor._client is None
+
+    @pytest.mark.asyncio
+    async def test_start_from_error_state_cleans_up(self):
+        """start() after ERROR should clean up stale state before retrying."""
+        from integrations.chat_bridge.vendors.discord import DiscordVendor
+
+        vendor = DiscordVendor()
+        vendor._state = PlatformState.ERROR
+        # Stale client from previous failed attempt
+        mock_old_client = MagicMock()
+        mock_old_client.is_closed.return_value = False
+        mock_old_client.close = AsyncMock()
+        vendor._client = mock_old_client
+
+        # start() should clean up the old client even though discord.py import
+        # will fail (we're in test mode with MagicMock stub)
+        with patch.dict("sys.modules", {"discord": None}):
+            result = await vendor.start(token="fake-token")
+
+        assert result is False
+        mock_old_client.close.assert_called_once()
+
     def test_get_oauth2_url_no_client(self):
         from integrations.chat_bridge.vendors.discord import DiscordVendor