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fix(mcp): emit type:object for oneOf and object properties so MCP clients send objects, not strings #3192

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fix(mcp): emit type:object for oneOf and object properties so MCP clients send objects, not strings #3192

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20 changes: 14 additions & 6 deletions apps/mcp/src/tools/intent.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -50,10 +50,15 @@ function jsonSchemaPropertyToZod(prop: Record<string, unknown>): z.ZodTypeAny {
}
}

// Complex schemas (oneOf, anyOf, allOf) — pass through as opaque;
// DocumentApi validates the actual payload at dispatch time.
// Complex schemas (oneOf, anyOf, allOf) — pass through as a loose object.
// z.unknown() emits a JSON Schema with no `type` field, which some MCP
// clients (notably the Claude Code harness) treat as a string and fail
// to JSON-encode object payloads. z.looseObject({}) emits
// {type: "object", additionalProperties: true}, so the value reaches
// the server as an object. DocumentApi validates the actual payload
// at dispatch time.
if (prop.oneOf || prop.anyOf || prop.allOf) {
return desc ? z.unknown().describe(desc) : z.unknown();
return desc ? z.looseObject({}).describe(desc) : z.looseObject({});
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@chatgpt-codex-connector chatgpt-codex-connector Bot May 7, 2026

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P1 Badge Preserve scalar oneOf schemas

When a catalog property uses oneOf for scalar variants, this branch now maps it to z.looseObject({}) and MCP validation rejects valid scalar arguments before DocumentApi dispatch. I checked apps/mcp/src/generated/catalog.ts: superdoc_comment.text and superdoc_create.text are string/string unions, superdoc_list.level is an integer union, and superdoc_table.color/cellSpacingPt allow string/number/null, so calls like superdoc_comment { action:"create", text:"...", target:{...} } will fail on text even though only object unions needed the object type hint. Please restrict the loose-object fallback to unions whose variants are objects, or preserve/recurse scalar union types.

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}

switch (type) {
Expand All @@ -69,9 +74,12 @@ function jsonSchemaPropertyToZod(prop: Record<string, unknown>): z.ZodTypeAny {
// z4-mini toJSONSchema cannot convert z.record() from zod v4 classic.
return desc ? z.array(z.unknown()).describe(desc) : z.array(z.unknown());
case 'object':
// Use z.unknown() instead of z.record() to avoid MCP SDK Zod v4 classic/mini
// incompatibility. DocumentApi validates the actual shape at dispatch time.
return desc ? z.unknown().describe(desc) : z.unknown();
// Use z.looseObject({}) so the emitted JSON Schema carries
// `type: "object"`. z.unknown() drops the type (clients treat it
// as a string); z.record() can't be converted by the MCP SDK's
// z4-mini toJSONSchema. DocumentApi validates the actual shape
// at dispatch time.
return desc ? z.looseObject({}).describe(desc) : z.looseObject({});
default:
return desc ? z.unknown().describe(desc) : z.unknown();
}
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