feat: Context API - simplified types (alternative to #1241)

[felixweinberger]

Summary

Alternative implementation of the Context API from PR #1241, using plain types and POJOs instead of a class hierarchy.

This PR replaces the flat RequestHandlerExtra type with a structured context system using 4 types:

Type	Description
BaseContext	Common context for all handlers (session, mcpReq, http, task, notification)
ServerContext	Extends BaseContext with server-specific methods (logging, elicitation, sampling, SSE controls)
ClientContext	Type alias for BaseContext with client-specific generics
TaskContext	Task-related fields (id, store, requestedTtl)

Key differences from #1241

Aspect	PR #1241	This PR
Implementation	Abstract class hierarchy (BaseContext class → ServerContext/ClientContext subclasses)	Plain types with POJO construction
Type count	~13 types/interfaces/classes	4 types
Construction	new ServerContext(...) / new ClientContext(...)	Plain object literals with closures
Type checking	ctx instanceof ServerContext	Duck-type checks ("elicitInput" in ctx.mcpReq)
Method sharing	Prototype-based (shared across instances)	Closures per request (same as current RequestHandlerExtra)

Context structure (same nested grouping as #1241)

ctx.sessionId
ctx.mcpReq.id / .method / ._meta / .signal / .send()
ctx.http?.authInfo / .req / .closeSSE / .closeStandaloneSSE  // server only
ctx.task?.id / .store / .requestedTtl
ctx.notification.send() / .log() / .debug() / .info() / ...  // logging on server only
ctx.mcpReq.elicitInput() / .requestSampling()                // server only

Motivation

• Simpler: 4 types vs ~13 — easier to understand and maintain
• Consistent: Keeps the POJO+closure pattern from the existing RequestHandlerExtra
• Same API surface: Users get the same nested structure and convenience methods
• No runtime overhead: No class instantiation, prototype chains, or instanceof checks

Breaking Changes

Same breaking changes as #1241 — RequestHandlerExtra properties move to the nested context structure.

How Has This Been Tested

• All existing tests updated and passing (497 tests)
• pnpm check:all (typecheck + lint) passes
• pnpm test:all passes

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

[changeset-bot]

🦋 Changeset detected

Latest commit: d9abbf4

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

This PR includes changesets to release 8 packages

Name	Type
@modelcontextprotocol/express	Patch
@modelcontextprotocol/hono	Patch
@modelcontextprotocol/node	Patch
@modelcontextprotocol/eslint-config	Patch
@modelcontextprotocol/test-integration	Patch
@modelcontextprotocol/client	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/core	Patch

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commit: d9abbf4

[felixweinberger]

this just moved out of protocol into packages/core/src/experimental/requestTaskStore.ts