[BlueX888]

Summary

registerTool() / registerPrompt() schemas (and elicitation requestedSchema) that are themselves already-converted JSON Schema documents — most prominently the output of zod's toJSONSchema(), which retains a ~standard prop whose converters reference the original zod schema — were re-converted through those converters on every tools/list and toolInputSchemaJson() call, instead of being used directly (#3132).

standardSchemaToJsonSchema() now detects a JSON Schema document by its own $schema / properties keywords and uses it as-is, before consulting ~standard.jsonSchema. Live Standard Schemas cannot be misdetected this way: zod schemas carry def, valibot uses entries, and ArkType nodes are functions — none expose $schema or properties at the root.

Fixes #3132

Behavior notes

• For a toJSONSchema() document the advertised schema is now the document itself. For example, additionalProperties: false that zod emits is preserved as registered — matching the documented fromJsonSchema() contract — where the previous re-conversion path dropped it.
• The same direct use applies to elicitation requestedSchema: a document carrying root-level constraints elicitation does not support (e.g. additionalProperties) now fails with the documented unsupported-constraint error — the same treatment a raw JSON Schema already receives — where the previous re-conversion silently dropped them.
• Documents with neither $schema nor properties (e.g. an openapi-3.0-style scalar root) keep the previous best-effort re-conversion behavior.

Testing

• packages/core-internal/test/util/standardSchema.test.ts: a toJSONSchema() document is used directly with zero converter invocations; a live zod schema still converts exactly once.
• packages/server/test/server/lazyToolSchemaConversion.test.ts: the reporter's scenario — registerTool with a pre-converted document, then toolInputSchemaJson() and tools/list, each with zero converter invocations.
• Full core-internal and server suites pass (the two pre-existing core-internal conformance failures are identical on unpatched main); tsgo, eslint and prettier are clean. The reporter's 1000-tool MRE drops from ~7.8 ms to ~1.9 ms of conversion work.

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🦋 Changeset detected

Latest commit: 26564b0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@modelcontextprotocol/core-internal	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/client	Patch
@modelcontextprotocol/codemod	Patch
@modelcontextprotocol/core	Patch
@modelcontextprotocol/server-legacy	Patch

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