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fix: accept metadata on legacy conformance initialize #20

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fix: accept metadata on legacy conformance initialize #20

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5 changes: 5 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,11 @@ and this project uses [Semantic Versioning](https://semver.org/spec/v2.0.0.html)

## [Unreleased]

### Fixed

- Accept optional request metadata on session-era `initialize` requests in the
pinned conformance fixture instead of misclassifying them as modern traffic.

## [0.5.0] - 2026-09-16

### Added
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32 changes: 27 additions & 5 deletions docker/mcp-conformance.patch
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Expand Up @@ -24,12 +24,32 @@
// Stateless (draft) operations whose results MUST carry the SEP-2549 caching
// hints (`ttlMs`, `cacheScope`).
const STATELESS_CACHEABLE_METHODS: ReadonlySet<string> = new Set([
@@ -1283,8 +1291,42 @@
meta === undefined &&
reqVersion !== undefined &&
LEGACY_SESSION_PROTOCOL_VERSIONS.includes(reqVersion);
@@ -1276,15 +1284,57 @@
const meta = params._meta;
const metaVersion = meta?.['io.modelcontextprotocol/protocolVersion'];
-
- if (!sessionId && (reqVersion || meta) && !isLegacySessionEraRequest) {
+
- // A request that carries no `_meta` and names a legacy session-era revision
- // in the header is legacy traffic; it is served by the session path below
- // instead of being rejected for missing per-request metadata.
+ // An initialize request negotiates its version in params and may carry the
+ // optional RequestParams `_meta` field. Route session-era versions through
+ // the stateful transport even when that metadata is present.
+ const isLegacyInitializeRequest =
+ isInitializeRequest(body) &&
+ typeof params.protocolVersion === 'string' &&
+ LEGACY_SESSION_PROTOCOL_VERSIONS.includes(params.protocolVersion);
+
+ // A non-initialize request that carries no `_meta` and names a legacy
+ // session-era revision in the header is also legacy traffic.
const isLegacySessionEraRequest =
- meta === undefined &&
- reqVersion !== undefined &&
- LEGACY_SESSION_PROTOCOL_VERSIONS.includes(reqVersion);
+ isLegacyInitializeRequest ||
+ (meta === undefined &&
+ reqVersion !== undefined &&
+ LEGACY_SESSION_PROTOCOL_VERSIONS.includes(reqVersion));
+ const isModernEraRequest =
+ !sessionId && (reqVersion !== undefined || meta !== undefined) &&
+ !isLegacySessionEraRequest;
Expand Down Expand Up @@ -64,7 +84,9 @@
+ }
+ });
+ }
-
+
- if (!sessionId && (reqVersion || meta) && !isLegacySessionEraRequest) {
+ if (isModernEraRequest) {
// Missing Transport Header Validation Check
if (!reqVersion) {
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