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* fix(mcp): MCP's long-lived streams keep alive and take a stream admission slot (BUG-3835) An idle MCP event stream made no write, so #2182's write deadline never fired on it: a client that stopped reading but held TCP open pinned a handler goroutine and its session until a notification happened to be written, and a signed-in client could open any number of them. - A ': keepalive' comment at the /events cadence on any response the transport commits as 200 text/event-stream, written through the same bounded writer. mcp-go writes each SSE event with one Write, so a mutex at Write boundaries keeps keepalives between events. No keepalive after a JSON-RPC response (the final event of a POST stream) or after the handler returns. mcp-go's own heartbeat is not used: it sends ping requests every client must answer. - The shared streamAdmission gate, keyed by streamPrincipal, taken at request entry for the two long-lived doors: GET /mcp and a subscriptions/listen POST. A refusal is the same plain 429 sse_limit_exceeded with Retry-After 5, sent before the transport runs. A tool call upgraded to SSE mid-call is not counted: a refusal there would land after its side effects. Listen is detected by decoding the whole body exactly as mcp-go does (encoding/json into a "method" field), not by a fixed-size peek that key order could evade. - Docs, config, the startup log and the metric help say the budget now covers MCP's long-lived streams. Credential expiry for /mcp streams is BUG-3837. Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * docs(mcp): the keepalive's shutdown window, the event-store premise and the chatgpt mount, stated precisely (BUG-3835) Codex r1 (Medium, proposed declined): a keepalive tick between the transport's return and end() can add one comment frame; it is still inside mcpBoundWrites, which joins the keepalive goroutine before returning, so net/http never sees a write after the handler. The comments now say so. Codex r1 (Low): GET /mcp/chatgpt is admitted too; the docs named only /mcp. Hunter r1: the one-Write premise holds only without an event store (writeSSEEventRaw writes twice); stated at the premise. Detection of a stalled idle client takes up to about three keepalive intervals; stated in docs/api.md. Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * fix(mcp): a panicking transport stops the keepalive; MCP streams are stated long-lived without a credential re-check (BUG-3835) Hunter r2 (Low-Medium): the keepalive shutdown ran after next.ServeHTTP without defer, so a panicking transport left it running past the handler, with chi's Recoverer swallowing the panic. Now deferred; pinned by TestMCP_BUG3835_PanickingTransportStopsTheKeepalive (red when not deferred). Hunter r2 (Medium): docs/api.md and two code comments said no MCP route is long-lived. The MCP transport's GET and subscriptions/listen streams are, and do not yet re-check their credential; that is BUG-3837. Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * docs(mcp): the keepalive catches dead peers; a live non-reader is bounded by the budget, not detected (BUG-3835) r3 hunter Medium: with default socket buffers a comment every 30s takes days to fill them, so the "caught within about three keepalive intervals" claim held only in the shrunk-buffer tests. api.md, the file header comment and the stalled-reader test comment now say what the keepalive catches and what the budget bounds. Codex r3 Low: deployment.md's stream gauge and checklist now include MCP's long-lived streams. The end()/ended comments state the one-frame window between the transport's return and end(). Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * fix(mcp): the admission body read is in the body census; dead-peer detection is stated as TCP gives it (BUG-3835) r4 blind hunter: - M1: mcpLongLivedRequest reads the request body and was not in the body reader census, so TestEveryRequestBodyReaderIsAccountedFor failed. It is now listed, with the reason and the second-buffer cost the lead accepted. - M3: a half-open peer accepts keepalive writes into the socket buffer until TCP gives up on it; "within one keepalive plus the write deadline" held only in the shrunk-buffer tests. api.md and the header comment now say so. - L3: the panicking-transport test waits for its first keepalive, read under the writer's mutex, instead of sleeping a fixed 10ms (M7 still red). Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * fix(mcp): admission reads a POST body only when its protocol header is modern; r6 fixes (BUG-3835) Pad serves the legacy MCP protocol versions only, and mcp-go serves a subscriptions/listen only on a modern-era POST whose Mcp-Protocol-Version header is modern and matches _meta. So a POST without a modern header is never a listen, and admission no longer reads its whole body a second time (r6 hunter M1, gate approved by the lead). The docs, the metrics help, the startup log and the census reason say listen is counted once the modern era is served. api.md states the keepalive outlives a proxy idle timeout until BUG-3837, the deployment note says the per-user bucket is shared with the browser's /events, and a test pins isFinalSSEEvent against the real transport's response frame. Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * fix(mcp): admission looks for a listen only on a protocol version the transport serves; r7 fixes (BUG-3835) The listen gate now also requires the header's version to be one the mount's transport serves, read through mcp-go's SupportsProtocolVersion (forwarded through the ChatGPT wrapper). A client probing an unserved modern version at a full budget reaches mcp-go and gets the 400 it falls back on, not a 429 (r7 ruling). Pad serves the legacy versions only, so no POST body is read for admission today, which the docs now say. New tests pin that mcp-go never serves a listen without a modern header (with a control that it serves a well-formed one), that an unserved modern version is not read or counted, and that both production mounts report their served versions. Claude-Session: https://claude.ai/code/session_01Rj4CMyK2EqxerMihbGs3Kr * test(mcp): the served-version gate is checked against the transports pad server mounts (BUG-3835) r8 L2 (lead ruling): internal/mcp's wiring test builds its own transports, so a shim around either production binding would silently send admission back to counting every modern version. Server.MCPMountServesVersion exposes the gate's read of the transport the server holds, and a cmd/pad test drives wireMCP and asserts both /mcp and /mcp/chatgpt report their versions. Shim mutants on each binding turn it red. Claude-Session: https://claude.ai/code/session_012QxKpjqXTpU84auY5zZ8FR * docs(mcp): the bus and mcpBoundWrites comments name the MCP stream slot and keepalive (BUG-3835) r5 hunter 3 and hunter 6's doc half, accepted by the lead (16:04Z): internal/events/bus.go said streamAdmission is acquired by "both endpoints", falsified once MCP's long-lived streams acquire it too, and mcpBoundWrites' doc comment did not mention the admission slot or the keepalive. Comment-only. Claude-Session: https://claude.ai/code/session_012QxKpjqXTpU84auY5zZ8FR * docs(api): the stream budget's 429 is stated once, and the MCP keepalive has its own paragraph (BUG-3835) r5 hunter 2, accepted by the lead (16:04Z): the admission paragraph stated the 429 refusal twice, the second time after the keepalive text it no longer fitted. Docs-only. Claude-Session: https://claude.ai/code/session_012QxKpjqXTpU84auY5zZ8FR