fix: refuse standalone GET on the MCP endpoint with 405 (#136)

[hellices]

Fixes #136

Problem

Quitting korvid while an external MCP host held a standalone GET /mcp connection printed two ERROR tracebacks over the terminal ("Exception in ASGI application" + a lifespan CancelledError).

Chain (reproduced deterministically):

1. The mcp SDK (1.28.x) serves GET as an infinite standalone SSE stream even in stateless mode with json_response=True — a stream this server never sends anything on (no server-initiated messages exist by construction).
2. korvid neutralizes uvicorn's signal capture (the TUI owns signals), so sse-starlette's shutdown watcher (signal-based) never fires and the stream never closes on should_exit.
3. uvicorn's graceful shutdown (timeout_graceful_shutdown=None) waits forever on the open connection, MCPController.shutdown()'s 5 s deadline falls back to a hard task.cancel(), and the CancelledError escapes the SSE task group and the lifespan.

Fix

Answer anything but POST with 405 Method Not Allowed in the ASGI wrapper, before the SDK session manager. Spec-sanctioned:

The server MUST either return Content-Type: text/event-stream in response to this HTTP GET, or else return HTTP 405 Method Not Allowed, indicating that the server does not offer an SSE stream at this endpoint.

The TypeScript SDK's stateless mode does exactly this (405 for non-POST before any transport is constructed); upstream python-sdk PR modelcontextprotocol/python-sdk#3129 addresses only the stateful pre-session GET, so the stateless path needs this server-side guard.

Tests

• test_get_is_refused_with_405_instead_of_an_sse_stream — GET gets 405, not an SSE stream.
• test_shutdown_completes_while_a_client_holds_a_get_connection — regression: graceful shutdown completes within the controller deadline (previously hung forever, then hard cancel, then tracebacks).

Full gate (make check) green: ruff, mypy, 2794 passed / 21 skipped, tach.

[Copilot]

Pull request overview

Refuses non-POST MCP requests to prevent infinite GET SSE streams from blocking shutdown.

Changes:

• Returns HTTP 405 with Allow: POST for non-POST requests.
• Adds GET rejection and shutdown regression tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/korvid/mcp/server.py	Adds the HTTP method guard.
tests/mcp/test_server.py	Adds GET and shutdown coverage.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[my-reviewer-agent]

issue #136의 근본 원인(stateless+json_response 모드에서 SDK가 GET을 무한 standalone SSE 스트림으로 서빙 → uvicorn graceful shutdown이 영원히 대기 → hard cancel → ASGI 예외 트레이스백)을 정확히 짚고, 스펙이 허용하는 405 거부를 세션 매니저 앞단 ASGI 래퍼에서 처리한 깔끔한 수정입니다.

특히 좋은 점:

• 보안 순서 보존: 405 응답 전에 TransportSecurityMiddleware.validate_request로 동일한 DNS-rebinding Host/Origin 검증을 먼저 수행 — 악성 origin은 405로 응답받는 대신 403으로 거부되며, test_hostile_origin_get_is_rejected_not_answered_405가 이 순서를 고정합니다.
• 회귀 테스트의 실질성: test_shutdown_completes_while_a_client_holds_a_get_connection은 GET 연결을 실제로 열어둔 채(response_started 이벤트로 헤더 수신 확인) shutdown을 요청하고 hard-cancel 폴백 데드라인(5s) 안에 graceful 완료를 단언하므로, 수정 전 코드에서는 타임아웃으로 실패하는 진짜 RED 테스트입니다.
• scope["type"] == "http" 가드로 lifespan/websocket scope는 건드리지 않고, Allow: POST 헤더도 스펙대로 포함.

사소한 참고(비차단): 405 경로가 GET뿐 아니라 DELETE(stateful 세션 종료용 메서드)도 거부하지만, 이 서버는 stateless라 세션 종료 개념 자체가 없으므로 올바른 동작입니다.

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