test: convert test_integration.py to in-memory transport (fix flaky)

[maxisbey]

Summary

Converts tests/server/mcpserver/test_integration.py from subprocess+TCP to the in-memory Client(mcp) pattern, eliminating port-race flakiness under pytest-xdist.

Closes #1776.

Root Cause

The server_port fixture allocates a port by binding to 0 then releasing the socket before the subprocess can bind it:

@pytest.fixture
def server_port() -> int:
    with socket.socket() as s:
        s.bind(("127.0.0.1", 0))
        return s.getsockname()[1]  # socket closed → port released → TOCTOU window

With pytest -n auto, another xdist worker's subprocess can grab the same port first. wait_for_server only checks TCP connect, so it happily accepts a connection to the wrong server. CI evidence in job 66317185239 shows a 7ms 404 on /sse — not enough time for a subprocess to start, meaning wait_for_server saw a different worker's server.

Verification this is a port race, not a uvicorn lifespan gap

mcp.sse_app() returns Starlette(routes=routes) with no lifespan — routes are synchronously constructed. Uvicorn+Starlette never serves 404 before 200 for a no-lifespan app; a 404 on /sse can only mean a different server bound that port.

Fix

None of these 20 parametrized tests (10 × 2 transports) exercise transport-specific behavior — they test MCP protocol features (tools, resources, prompts, progress, sampling, elicitation, notifications, completion, structured output). Converted all to use Client(mcp) in-memory, matching the established pattern in test_server.py (×16) and test_url_elicitation.py (×11).

Transport behavior remains covered separately in tests/server/test_sse_security.py, test_streamable_http_{manager,security}.py, and tests/shared/test_{sse,streamable_http,ws}.py.

Impact

	Before	After
Tests	20 (parametrized over 2 transports)	10
Runtime	~20s (subprocess spawn + uvicorn startup)	~0.5s
Lines	643	359 (−284)
Flakiness	Port race under xdist	None (in-process, deterministic)

_{AI Disclaimer}

[claude]

LGTM — straightforward test refactor from subprocess+TCP to in-memory transport, following the established Client(mcp) pattern.

Extended reasoning...

Overview

This PR touches two files: a one-line pragma removal in src/mcp/server/session.py (removing # pragma: no cover from send_resource_list_changed since the method is now exercised by the converted tests), and a significant simplification of tests/server/mcpserver/test_integration.py that replaces subprocess+TCP test infrastructure with in-memory Client(mcp) calls, reducing the file from 643 to 359 lines.

Security risks

None. The production code change is a single pragma comment removal. All other changes are test-only, removing network-based test infrastructure in favor of in-memory transport.

Level of scrutiny

Low scrutiny warranted. This is a mechanical test refactor that follows an established pattern already used in test_server.py and test_url_elicitation.py. The test assertions are preserved; only the transport mechanism changes. The motivation (port-race flakiness under pytest-xdist) is well-documented with CI evidence.

Other factors

The PR removes ~100 lines of test infrastructure (fixtures, subprocess management, port allocation, transport selection helpers) while preserving all 10 test scenarios and their assertions. Transport-specific coverage is noted as remaining in dedicated test files (test_sse_security.py, test_streamable_http_*.py, tests/shared/test_{sse,streamable_http,ws}.py). No bugs were found by automated analysis.