fix: use negotiated protocol version in server-sse-polling raw requests - #416
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The server-sse-polling scenario hard-coded mcp-protocol-version: 2025-11-25 on its raw tools/call POST and Last-Event-ID reconnection GET instead of the version negotiated during initialize — the same bug class as #412. A server that enforces the negotiated session version rejects those requests once it negotiates any other version. Read transport.protocolVersion after client.connect() and use it for both raw request headers, falling back to the run's spec version, mirroring the sse-multiple-streams fix (#415). Add a regression test whose fixture server down-negotiates to 2025-06-18 and 400s any request whose MCP-Protocol-Version header does not match, so a fix that hard-codes the latest version cannot pass. Follow-up to #415. Co-Authored-By: Claude <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0178cz8nAyFRHQyq9cg2XgZz
commit: |
Enforce session id alongside protocol version in the fixture, record Last-Event-ID presence per GET so the SDK's automatic standalone GET cannot satisfy the reconnect assertion, normalize the header type instead of casting, return a descriptive 400 body on the GET path, add Allow to 405s, use the spec-shaped empty-data priming event, and read sessionId via the SDK's public getter in the scenario. Co-Authored-By: Claude <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0178cz8nAyFRHQyq9cg2XgZz
pcarleton
approved these changes
Jul 27, 2026
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Requested by Paul Carleton · Slack thread
Before
The
server-sse-pollingscenario initialized through the SDK'sStreamableHTTPClientTransportbut hard-codedmcp-protocol-version: 2025-11-25on its two raw follow-up requests — thetools/call test_reconnectionPOST and theLast-Event-IDreconnection GET. Against a stateful server that enforces the version negotiated during initialize, those requests are rejected the moment the negotiated version is anything other than2025-11-25: the 400 on the POST is misreported as "server does not implement test_reconnection tool" (WARNING) and the scenario ends before testing any polling behavior. This is the same bug class as #412, fixed forserver-sse-multiple-streamsin #415.After
Both raw requests carry the version actually negotiated during initialize, so version-enforcing servers get their SSE polling behavior genuinely exercised. Servers that don't enforce the version are unaffected.
How
In
src/scenarios/server/sse-polling.ts, afterclient.connect(transport)the scenario reads the SDK transport's publicprotocolVersiongetter intonegotiatedProtocolVersion(alongside the session-id extraction, now via the publicsessionIdgetter) and uses it for themcp-protocol-versionheader on the raw POST and reconnection GET, falling back to the run'sspecVersionif the transport exposes none — mirroring the merged #415 pattern exactly.src/scenarios/server/sse-polling.test.tsadds regression coverage with a hardened fixture: the fixture server down-negotiates every initialize to2025-06-18regardless of the proposed version, records each follow-up request'sMCP-Protocol-Versionheader (and, for GETs,Last-Event-IDpresence, so the SDK's automatic standalone GET cannot satisfy the reconnect assertion), and 400s any version or session-id mismatch — so a wrong fix that hard-codes the latest version cannot pass. The fixture serves a spec-shaped priming event (id + empty data) then closes the stream without the tool result, forcing the scenario down theLast-Event-IDreconnection GET path so both fixed sites are exercised. Verified the test fails against the previous scenario code with either site regressed individually. A second test pins that the fixture rejects the supported-but-non-negotiated latest version.Also verified end-to-end against the in-repo everything-server (
examples/servers/typescript) on this branch:server-sse-pollingpasses 3/3 (priming event, retry field, disconnect-resume), so lenient servers see no behavior change.Follow-up to #415; same bug class as #412.