fix: Gemini requires parameters of type Array to provide schemas for array elements

[vlymar]

We saw an error in cursor that referenced the create_sms_step_in_workflow tool.

And I saw this error in Zed:

Error interacting with language model
failed to stream completion
error during streamGenerateContent, status code: 400, body: {
  "error": {
    "code": 400,
    "message": "* GenerateContentRequest.tools[0].function_declarations[21].parameters.properties[blocks].items: missing field.\n",
    "status": "INVALID_ARGUMENT"
  }
}

If you combine the zed error message with the cursor error message you see that there's a problem with the blocks parameter of the create_sms_step_in_workflow tool.

After a bit of digging I found that Gemini has a history of being quite picky with the subset of OpenAPI that it supports.

Loom showing the mcp error failing against a locally version of the MCP server, then succeeding when I checkout and build this branch.

References

• https://ai.google.dev/gemini-api/docs/function-calling?example=meeting#function_declarations
• https://ai.google.dev/api/caching#Schema
• https://discuss.ai.google.dev/t/function-calling-issues-with-type-object-and-array/34581

[linear]

KNO-8641 [MCP] Issue with MCP in gemini

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[vlymar]

sorry, my editor deleted a bunch of whitespace

[vlymar]

this is the key fix .array(z.any()) does not work

[vlymar]

This is not a comprehensive schema for content blocks, but it demonstrates that the mcp server starts working once some schema is provided.

[vlymar]

I attempted to create a schema for content blocks, but I couldn't get one to work. I suspect that zod is emitting an openapi schema that isn't compatible with gemini for this union type (or I have some other bug here).

Specifically, items.anyOf looks sus. Googles docs show that the items field should contain Schema types, and while anyOf is a field on Schema, I don't think its valid for it to be the only field present. There's probably a clever re-expression of this schema that would be compatible with google's Schema but I ran out of time to figure it out.