Stop evicting standalone MCP listeners - #1754
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The agents@0.17.3 patch was rewritten on main by UsefulSoftwareCo#1754 (standalone listeners attach alongside each other instead of superseding, plus the _replayInFlight guard). Re-rolled this branch's change with bun patch on top of main's patched dist rather than merging the patch file textually: the Last-Event-ID branch no longer drains other streams, and the helper is now replayUndeliveredResponsesOnFreshGet, called only from the cursorless GET path. The fresh-GET fallback and its in-flight guard are unchanged.
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Problem
Every standalone SSE listener (bare GET) on a streamable-HTTP session shares one stream id, and
handleGetRequestapplied latest-listener-wins to it: each new listener closed the previous one. Clients that hold two listeners — mcp-remote opens one at connect and a second when it forwardsnotifications/initialized— evict each other forever, since every eviction triggers the SDK reconnect that evicts the other side. One production session showed ~55,600 listener GETs over 6.75h (~2.3/s) against 106 POSTs, and the affected user saw permanent disconnect/reconnect churn. Reproduced end-to-end with stockmcp-remote 0.1.37: a 4-minute idle session settles into ~0.8 GET/s with every response delivered twice.Fix
In
patches/agents@0.17.3.patch:supersedePriorStreamConnectionsonly applies to single-owner POST streams. Dead listeners are reaped by keepalive write failures and max-age rotation.sendStandaloneroutes server-initiated messages to the newest attachment (most likely live), still exactly one stream per message.onConnectcloses the WS with 1011 when the transport is missing instead of silently dropping the request, which previously left clients hanging ~30s against a half-initialized DO.Verification
repro-listener-supersede.test.ts: two reconnecting listeners previously produced 1,581 stream opens in 15s (median life 16ms); with the fix both stay open (passes; single-listener control unchanged).mcp-remote 0.1.37, one routine deploy mid-run — 20 GETs over 6 minutes (was 1,049 in 9.5 min), tool calls keep working through the deploy, GET rate settles instead of ramping.format:check,lint,typecheck,testall green.