fix(@ai-sdk/mcp): add resource_link content type to CallToolResultSchema#14928
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aayush-kapoor merged 3 commits intoMay 5, 2026
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The MCP spec defines resource_link as a content type variant, but CallToolResultSchema and PromptMessageSchema only accepted text, image, and embedded resource. With zod >= 4.4.x (within the declared peer-dep range), the missing union arm causes hard rejection when an MCP server returns resource_link content parts. Add ResourceLinkContentSchema to both unions. Fixes vercel#14925
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Per the MCP 2025-11-25 schema, 'name' is a required field on resource_link content (alongside 'type' and 'uri'). Update the Zod schema to match.
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…ema (#14928) ## Summary Adds the MCP spec's `resource_link` content type to `CallToolResultSchema` and `PromptMessageSchema` unions. ## Problem `CallToolResultSchema` only accepts `text`, `image`, and `resource` (embedded) content types. The MCP specification defines a fourth variant — `resource_link` — which servers may return. With zod ≥ 4.4.x (within the declared peer-dep range `^3.25.76 || ^4.1.8`), unknown discriminated union variants are hard-rejected, causing `Failed to parse server response` errors from `callTool()`. ## Fix - Add `ResourceLinkContentSchema` (`{ type: 'resource_link', uri, name?, description?, mimeType? }`) - Include it in `CallToolResultSchema.content` array union - Include it in `PromptMessageSchema.content` union ## Testing The schema change is purely additive (new union variant). Existing tests pass unchanged since they don't produce `resource_link` content. The fix allows servers that do return `resource_link` parts to work correctly. Closes #14925 --------- Co-authored-by: Aayush Kapoor <83492835+aayush-kapoor@users.noreply.github.com>
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✅ Backport PR created: #15008 |
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…lResultSchema (#15008) This is an automated backport of #14928 to the release-v6.0 branch. FYI @kagura-agent Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> Co-authored-by: Aayush Kapoor <83492835+aayush-kapoor@users.noreply.github.com>
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Summary
Adds the MCP spec's
resource_linkcontent type toCallToolResultSchemaandPromptMessageSchemaunions.Problem
CallToolResultSchemaonly acceptstext,image, andresource(embedded) content types. The MCP specification defines a fourth variant —resource_link— which servers may return. With zod ≥ 4.4.x (within the declared peer-dep range^3.25.76 || ^4.1.8), unknown discriminated union variants are hard-rejected, causingFailed to parse server responseerrors fromcallTool().Fix
ResourceLinkContentSchema({ type: 'resource_link', uri, name?, description?, mimeType? })CallToolResultSchema.contentarray unionPromptMessageSchema.contentunionTesting
The schema change is purely additive (new union variant). Existing tests pass unchanged since they don't produce
resource_linkcontent. The fix allows servers that do returnresource_linkparts to work correctly.Closes #14925