fix: Claude Code MCP compatibility (Tokio panic + capabilities format)#6
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Replace direct `runtime.block_on()` calls with `tokio::task::block_in_place()` wrapper in all 12 tool handler methods in McpServerImpl. The previous implementation would panic with "Cannot start a runtime from within a runtime" when any tool was called via tools/call, because the JSON-RPC handlers run inside an async context but the tool methods were trying to block on the current runtime. The fix uses `block_in_place()` which is designed for this exact scenario - it moves the blocking operation to a blocking thread pool while allowing the async runtime to continue processing. Affected methods: - launch_app - stop_app - get_app_logs - take_screenshot - get_window_info - send_keyboard_input - send_mouse_click - execute_js - get_devtools_info - monitor_resources - list_ipc_handlers - call_ipc_command Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Claude Code's MCP client fails to connect when capabilities fields
(resources, prompts, logging) are null. Other working MCP servers
like narsil-mcp use empty objects {} instead.
This fix changes the initialize response from:
"resources": null,
"prompts": null,
"logging": null
To:
"resources": {},
"prompts": {},
"logging": {}
Tested with `claude mcp list` - server now shows "✓ Connected".
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
Two fixes to enable Claude Code CLI compatibility:
Tokio runtime nesting panic - Tool handlers were calling
runtime.block_on()inside an async context, causing "Cannot start a runtime from within a runtime" panic. Fixed by wrapping withtokio::task::block_in_place().Capabilities null vs empty object - Claude Code's MCP client fails to connect when capabilities fields (
resources,prompts,logging) arenull. Changed to empty objects{}to match other working MCP servers like narsil-mcp.Test plan
claude mcp listshows "✓ Connected" instead of "✗ Failed to connect"Before
After
🤖 Generated with Claude Code