PR #353 - modelcontextprotocol/conformance

Renumbers the draft-revision error codes to match the allocation policy that landed in modelcontextprotocol/modelcontextprotocol#2907:

Error	Old	New
`HeaderMismatch`	`-32001`	`-32020`
`MissingRequiredClientCapability`	`-32003`	`-32021`
`UnsupportedProtocolVersion`	`-32004`	`-32022`

Motivation and Context

modelcontextprotocol/modelcontextprotocol#2907 partitions the JSON-RPC server-error range (-32000..-32019 legacy/implementation-defined, -32020..-32099 reserved for the MCP spec) and renumbers the draft-only codes accordingly. The conformance suite still pinned the pre-policy numbers, so a server returning the now-spec-mandated -32020/-32021/-32022 would fail checks that expect the old values, and the suite's own mocks and fixtures would emit codes the new spec text reserves for legacy implementation use.

What changed

npm run sync-schema -- f817239f re-vendors src/spec-types/draft.ts (the schema diff between the previous pin and f817239f is exactly the renumber plus the new allocation-policy doc comment). src/scenarios/server/http-standard-headers.ts already imported HEADER_MISMATCH from the vendored types, so its assertion picks up the new value automatically.
Every literal -32001/-32003/-32004 reference across the stateless mock, the everything-server fixture, the server-stateless and SEP-2243 server scenarios, the request-metadata client scenario, all affected tests, and the sep-2243.yaml/sep-2575.yaml requirement rows is updated to the new code.
The everything-client's negotiation retry now checks for -32022 only (the previous -32004 || -32001 tolerance for pre-dedicated-code servers is dropped — those numbers are now in the legacy sub-range and the paired mocks emit -32022).
src/seps/traceability.json is generated; it still carries the old text and is left for the scheduled refresh workflow per AGENTS.md.

How Has This Been Tested?

npm run check, npm run build, npm test — all green (293 tests).
node dist/index.js client --command "npx tsx examples/clients/typescript/everything-client.ts" --suite draft: identical to pre-change baseline (request-metadata 7/7 confirms the everything-client's -32022 retry check works against the mock's new emission).

Breaking Changes

For draft-revision servers under test: the suite now requires the post-#2907 codes. Servers still emitting the pre-policy -32001/-32003/-32004 values will fail the corresponding checks (or need an expected-failures entry) until they update — that's the intended outcome of the spec renumber. Dated 2025-x revisions are unaffected.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This is the "conformance pins for SEP-2243/SEP-2575 codes" follow-up named in modelcontextprotocol/modelcontextprotocol#2907's description.
#336 (the draft re-derivation of the server-stateless error-code table) should be rebased on top of this; its remaining content is then purely the precedence questions #2907 did not settle (which code applies when a missing _meta field and a present header overlap, and HeaderMismatch vs UnsupportedProtocolVersion precedence when both rules trigger).
No check ids or severities change here; the SHOULD/MUST split in sep-2243.yaml for the standard- vs custom-header error-code requirement is unchanged (renumber only).