fix: add | undefined to transport option callbacks for exactOptionalPropertyTypes

[Christian-Sidak]

Summary

Adds | undefined to optional callback type properties in WebStandardStreamableHTTPServerTransportOptions to support TypeScript projects using exactOptionalPropertyTypes: true.

Fixes#1397

Changes

WebStandardStreamableHTTPServerTransportOptions (packages/server/src/server/streamableHttp.ts):

• sessionIdGenerator?: (() => string) | undefined
• onsessioninitialized?: ((sessionId: string) => void | Promise<void>) | undefined
• onsessionclosed?: ((sessionId: string) => void | Promise<void>) | undefined

Corresponding private fields on the class and the test helper interface are updated to match.

Why

Without this fix, users with exactOptionalPropertyTypes: true get:

error TS2379: Argument of type '{ sessionIdGenerator: undefined; enableJsonResponse: true; }'
is not assignable to parameter of type 'WebStandardStreamableHTTPServerTransportOptions' with
'exactOptionalPropertyTypes: true'.
Types of property 'sessionIdGenerator' are incompatible.
Type 'undefined' is not assignable to type '() => string'.

This is the standard TypeScript pattern for exactOptionalPropertyTypes compatibility. The Transport interface in @modelcontextprotocol/core already follows this pattern -- this PR brings the server transport options in line.

Testing

• tsc --noEmit passes for both packages/core and packages/server
• No behavioral changes -- purely a type-level fix

[changeset-bot]

🦋 Changeset detected

Latest commit: b8cd277

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

This PR includes changesets to release 5 packages

Name	Type
@modelcontextprotocol/server	Patch
@modelcontextprotocol/express	Patch
@modelcontextprotocol/fastify	Patch
@modelcontextprotocol/hono	Patch
@modelcontextprotocol/node	Patch

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commit: b8cd277

[felixweinberger]

Hi thanks for this - could you add a changeset please? (patch should be enough)

[Christian-Sidak]

@felixweinberger changeset has been added (gentle-planets-rest.md, patch for @modelcontextprotocol/server). Should be good to go -- thanks!

[Christian-Sidak]

@felixweinberger just checking if this looks good now with the changeset added. All checks are passing. Thanks!

[Christian-Sidak]

Friendly bump, @felixweinberger -- changeset was added in the prior commit. All checks are passing. Happy to adjust anything if needed.

[Christian-Sidak]

Friendly bump, @felixweinberger -- the changeset was added in the April 10 commit. All checks are passing. Happy to adjust if needed.

Changeset applied