Copilot CLI couldn't handle BigInt in structured MCP response

[xj-ms]

Describe the bug

When a MCP server returns big numbers in its response, Copilot CLI cannot handle it and fails with the following error. All ongoing tasks will be aborted

Execution failed: TypeError: Do not know how to serialize a BigInt

Affected version

1.0.74-0

Steps to reproduce the behavior

Requires dotnet 10.

1. Clone the repo https://github.com/xj-ms/StructuredContentBigIntMcp
2. Launch Copilot CLI in the repo. The MCP server should be already configured with the local .mcp.json
3. Ask Copilot to call the return_big_numbers tool
4. Observe the failure

Expected behavior

No response

Additional context

No response