fix: apply schema transformation to MCP tools for Gemini compatibility

[mugnimaestra]

Summary

Follow-up fix to #11952 - MCP tools were bypassing the schema transformation pipeline entirely, so the nested array fix wasn't being applied to them.

Problem

PR #11952 added nested array handling to sanitizeGemini, but MCP tools still failed with Gemini because:

1. MCP tools are created via convertMcpTool() in mcp/index.ts
2. They were added directly to the tools object without going through ProviderTransform.schema()
3. The nested array fix in sanitizeGemini was never applied to MCP tool schemas

Error (still occurring without this fix)

GenerateContentRequest.tools[0].function_declarations[49].parameters.properties[values].items.items: missing field.
GenerateContentRequest.tools[0].function_declarations[50].parameters.properties[values].items.items: missing field.
GenerateContentRequest.tools[0].function_declarations[54].parameters.properties[initialData].items.items: missing field.

Solution

• Add optional model parameter to MCP.tools() and convertMcpTool() functions
• Apply ProviderTransform.schema() to MCP tool schemas before registration
• Pass input.model from prompt.ts to MCP.tools() call

Files Changed

File	Change
packages/opencode/src/mcp/index.ts	Add model parameter, apply schema transformation
packages/opencode/src/session/prompt.ts	Pass model to MCP.tools()

Testing

Verified with google-docs-mcp + Gemini 3 Flash on VPS:

Before (with only #11952 merged):

0.0.0-fix/gemini-nested-array-items-202602031444
Error: * GenerateContentRequest.tools[0].function_declarations[49].parameters.properties[values].items.items: missing field.

After (with this PR):

0.0.0-fix/mcp-tools-schema-transform-202602031607
> build · gemini-3-flash
Hello! How can I help you today?

Problematic MCP Tools (now fixed)

Tool	Parameter	Schema
writeSpreadsheet	values	array<array<any>> (2D array)
appendSpreadsheetRows	values	array<array<any>> (2D array)
createSpreadsheet	initialData	array<array<any>> (2D array)

Related

• Fixes the remaining issue from Error with Gemini models when MCP enabled #5832
• Follow-up to fix: handle nested array items for Gemini schema validation #11952

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[rekram1-node]

On your last pr you claimed u tested it manually? Now ur saying it didn't fix it...

?

[mugnimaestra]

On your last pr you claimed u tested it manually? Now ur saying it didn't fix it...

?

I am truly sorry that was my mistake before, it was not tested enough, here I put the recording

Screen.Recording.2026-02-03.at.23.39.46.mov

hope this can help 🙇

[rekram1-node]

/review

[github-actions]

lgtm

[rekram1-node]

@mugnimaestra can u test this:
#11984

It's a bit more minimal, keeps sanitization in the same place we sanitize the other tools

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.