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fix(mcp): tolerate invalid tool output schemas#26530

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nicolascancino wants to merge 4 commits into
anomalyco:devfrom
nicolascancino:fix/mcp-output-schema-ref
Closed

fix(mcp): tolerate invalid tool output schemas#26530
nicolascancino wants to merge 4 commits into
anomalyco:devfrom
nicolascancino:fix/mcp-output-schema-ref

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@nicolascancino nicolascancino commented May 9, 2026

Issue for this PR

Closes #26529

Type of change

  • Bug fix
  • New feature
  • Refactor / code improvement
  • Documentation

What does this PR do?

Makes MCP tool loading resilient when a server returns a valid tools/list response whose outputSchema contains refs the SDK cannot resolve.

The normal client.listTools() path still runs first. If it fails with a schema reference error, OpenCode retries tools/list with a tolerant result schema that keeps inputSchema validation and treats outputSchema as opaque.

This fixes Google Stitch-style failures where the MCP transport connects but OpenCode marks the server as failed while validating tool output schemas.

How did you verify your code works?

cd packages/opencode
bun test test/mcp/lifecycle.test.ts --timeout 30000

Result:

20 pass
0 fail
51 expect() calls
Ran 20 tests across 1 file. [2.13s]

Screenshots / recordings

N/A — non-UI change.

Checklist

  • I have tested my changes locally
  • I have not included unrelated changes in this PR

@kitlangton kitlangton mentioned this pull request May 9, 2026
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@kitlangton kitlangton enabled auto-merge (squash) May 9, 2026 23:16
@kitlangton kitlangton mentioned this pull request May 10, 2026
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kitlangton commented May 10, 2026

Thanks for putting this fix together. I opened #26614 based on this approach, rebased onto current dev, with a narrower fallback and additional regression coverage for both the Stitch-style schema-ref failure and the non-schema failure path.

Closing this one in favor of #26614 so we have a clean branch for merge. Credit to @nicolascancino for the original fix direction here.

@kitlangton kitlangton closed this May 10, 2026
auto-merge was automatically disabled May 10, 2026 01:20

Pull request was closed

@github-actions github-actions Bot mentioned this pull request May 10, 2026
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Successfully merging this pull request may close these issues.

MCP tools fail to load when outputSchema contains unresolved refs

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@nicolascancino @kitlangton