Implements Server-Sent Events (SSE) streaming for tool results that return async iterators, enabling real-time streaming of tool outputs through POST requests.
Key Features:
- Detects async iterators using Symbol.asyncIterator
- Automatic response type selection (JSON vs SSE)
- Streams each yielded chunk as separate SSE event
- Maintains backward compatibility with immediate JSON responses
- Robust error handling during streaming
- Per-session event ID tracking for SSE events
Files Added:
- test/async-iterator-streaming.test.ts: Comprehensive test suite (5 tests)
- examples/streaming-demo.ts: Working demonstration server
Files Modified:
- src/types.ts: Extended types for async generator support
- src/handlers.ts: Added streaming response detection and interface
- src/routes/mcp.ts: Implemented SSE streaming logic for POST responses
Testing:
- All 281 tests passing including 5 new streaming-specific tests
- Tests cover immediate responses, streaming, error handling, and event sequencing
- Demo server with curl examples for manual verification
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

Fixes critical MCP specification compliance issue where event IDs were assigned per-session instead of per-stream, breaking Last-Event-ID resumability.
Key Changes:
- Updated SessionStore interface to support per-stream tracking with StreamMetadata
- Added stream ID generation and management for each SSE connection
- Implemented per-stream event ID sequences starting from 1
- Modified message storage to organize by streamId, not just sessionId
- Updated replay logic to work with per-stream cursors
- Maintained backwards compatibility with legacy session-level methods
Per MCP Transport Specification:
- Line 169: "event IDs should be assigned by servers on a per-stream basis"
- Line 143: "client MAY remain connected to multiple SSE streams simultaneously"
- Line 145: "server MUST send each message on only one of the connected streams"
Files Modified:
- src/stores/session-store.ts: Added per-stream interface methods
- src/stores/memory-session-store.ts: Implemented per-stream storage
- src/stores/redis-session-store.ts: Added Redis per-stream support
- src/routes/mcp.ts: Per-stream SSE implementation with stream IDs
- test/per-stream-event-ids.test.ts: Test suite for per-stream compliance
Testing:
- 284/286 tests passing (2 Redis integration test failures to address)
- New per-stream test suite covering event ID architecture
- Fixed async iterator streaming test expectations
- Updated all session creation to include streams Map
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

Updates Redis integration tests to work with the new per-stream event ID architecture while maintaining backward compatibility.
Key Changes:
- Modified sendSSEToStreams to detect broadcast notifications and elicitation requests
- Added isBroadcast logic to use legacy session-level storage for notifications
- Updated sendSSEToStreamsLegacy to store messages in session history for backward compatibility
- Fixed tests expecting session-level message storage for broadcast/elicitation messages
Per-stream messages use per-stream storage, while broadcast notifications and elicitation requests use session-level storage to maintain compatibility with existing tests and expected behavior.
Testing:
- All 286 tests now passing
- Redis integration tests (7/7) passing
- Broadcast notifications properly stored in session history
- Elicitation requests properly stored in session history
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

The broadcast system is a core feature, not legacy. Updates terminology throughout:
- sendSSEToStreamsLegacy → sendSSEToStreamsBroadcast
- 'Legacy' comments → 'Broadcast' comments
- Clarifies that broadcast messages are session-wide by design
- Maintains same functionality with clearer naming
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

Adds detailed documentation for the new async iterator streaming feature:
Key additions:
- Async Iterator Streaming section with complete examples
- Basic streaming tool implementation patterns
- Advanced streaming examples (file processing, error handling)
- Client usage examples with curl commands
- Streaming response format explanation
- Key features and benefits overview
Documentation covers:
- Automatic async iterator detection
- Real-time SSE streaming capabilities
- Error handling during streaming
- Backward compatibility guarantees
- MCP specification compliance
- Performance and resumability features
Updated Features section to highlight:
- Async Iterator Streaming as a key feature
- Per-Stream Event IDs for MCP compliance
- Real-time streaming capabilities
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

Signed-off-by: Matteo Collina <hello@matteocollina.com>