Description

The Aspire MCP server enters an infinite tools/list request loop when the db-mcp container's tools become available. This causes VS Code to spin indefinitely on "list tools" and the Copilot CLI to intermittently fail to surface the db-mcp tools.

Environment

• Aspire CLI/SDK: 13.2.0-preview.1.26106.2
• VS Code: Insiders 1.110.0-insider
• OS: Windows
• MCP client: VS Code Copilot Chat + GitHub Copilot CLI

Reproduction Steps

1. Create an Aspire app with a PostgreSQL resource that has a db-mcp sidecar container
2. Start the AppHost (aspire run --detach)
3. Connect the Aspire MCP server to VS Code or Copilot CLI
4. Wait for the db-mcp container to register its tools

Observed Behavior

When the db-mcp container connects and registers its tools, the Aspire MCP server fires a notifications/tools/list_changed notification. The MCP client responds with a tools/list request, which the server handles. However, the server immediately fires another tools/list_changed notification, causing the client to request tools/list again — creating an infinite loop.

From the logs:

• 1,742 tools/list request handler calls in ~2 minutes 44 seconds
• 1,740 Tool list changed notifications in the same period
• The tool count oscillates between 14 (base) and 23 (base + 9 db-mcp tools), suggesting a race condition where the db-mcp tools are alternately visible and invisible during enumeration
• The loop only terminates when VS Code kills the MCP server process

Log excerpt (showing the tight loop):

2026-02-06 13:55:44.018 [info] Tool list changed, refreshing tools...
2026-02-06 13:55:44.018 [info] Discovered 14 tools
2026-02-06 13:55:44.020 [info] tools/list request handler completed.
2026-02-06 13:55:44.020 [info] tools/list request handler called.
2026-02-06 13:55:44.053 [info] Tool list changed, refreshing tools...
2026-02-06 13:55:44.053 [info] Discovered 23 tools
2026-02-06 13:55:44.054 [info] tools/list request handler completed.
2026-02-06 13:55:44.054 [info] tools/list request handler called.
2026-02-06 13:55:44.069 [info] Tool list changed, refreshing tools...
2026-02-06 13:55:44.069 [info] Discovered 14 tools
... (repeats 1740+ times over ~2m44s)

Termination stack trace:

System.OperationCanceledException: The operation was canceled.
   at System.Threading.CancellationToken.ThrowOperationCanceledException()
   at ModelContextProtocol.McpSessionHandler.SendMessageAsync()
   at ModelContextProtocol.McpSessionHandler.HandleRequest()
   at ModelContextProtocol.McpSessionHandler.HandleMessageAsync()

Additional Observations from Copilot CLI

In the Copilot CLI, the behavior manifests differently:

• refresh_tools sometimes returns 14 tools, sometimes 23
• When it returns 23, the db-mcp tool IDs are reported but calling them returns No MCP client found for tool ID or An error occurred invoking
• The tools_changed_notice is either never delivered to the CLI client, or arrives with stale tool IDs

Expected Behavior

1. The notifications/tools/list_changed notification should fire once when the db-mcp tools stabilize, not on every tools/list response
2. The tool list should be consistent — if 23 tools are reported, all 23 should be callable
3. No infinite loop between tools/list_changed → tools/list → tools/list_changed

Possible Root Cause

It appears the server is firing tools/list_changed as a side effect of handling the tools/list request itself (perhaps re-enumerating proxied tools from the db-mcp container triggers a change detection). This creates a feedback loop: list → changed → list → changed → ...

A debounce or dirty-flag mechanism on the tools/list_changed notification would likely resolve this.

Attached Logs

Full VS Code MCP log (10,547 lines) is available — happy to attach if needed.