fix(mcp): report invalid tool arguments

[Steve-whb]

Summary

• Report MCP tool schema validation failures as tool errors.
• Include validation paths in text and JSON error responses.

[Steve-whb]

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[pavelfeldman]

I like the intent, but the implementation is below the quality level we would usually accept. Handle zod errors in a nicely-typed manner here, do not declare primitive types.

[Steve-whb]

Thanks, updated this to narrow specifically on z.ZodError and type the formatter against Zod's own error/path types instead of a hand-rolled issue shape. Unexpected parse errors now preserve the previous behavior by rethrowing.

Validated with:

• npm run build
• npm run ctest-mcp validation
• npm run flint (code gates passed; local npm run doc still fails because WebKit crashes on this macOS setup with Bus error: 10)

[Skn0tt]

Could we use Zod's builtin formatter? https://zod.dev/error-formatting
We have custom formatting in the other place because we want to make it look like common CLI args errors, but that doesn't apply here.

[Steve-whb]

Sounds good, just updated it

[Skn0tt]

can you turn the tests into e2e tests like the rest of the codebase and assert against real tools?

[Steve-whb]

just updated it

[github-actions]

Test results for "MCP"

7207 passed, 1113 skipped

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Merge workflow run.