Review on #20379, finding 1 (High). Two ways an MCP config revision could
be silently acknowledged without ever being applied:
Client: the poll advanced its accepted mcp_rev BEFORE calling reload.mcp,
and quietRpc collapses failures to null — a reload that failed against a
temporarily broken server left the revision recorded as applied, and no
subsequent poll retried until an unrelated MCP edit. The handshake is now
syncMcpReload(): send the observed rev with the request, advance `accepted`
only when the server answers status=reloaded (to the server's loaded_rev,
falling back to the requested rev on older gateways), and re-compare on
EVERY poll tick — decoupled from mtime — so a transient failure heals on
the next tick. An in-flight guard stops the 5s poll from stacking requests
behind a slow reload.
Server: generation-only coalescing let a follower triggered by revision B
ack against revision A's registry when the config changed under a slow
leader. The leader now re-hashes the MCP-relevant config after discovery
and repeats until stable (bounded), records _mcp_reload_loaded_rev, and a
follower coalesces only when the revision it was asked to load matches —
otherwise it re-runs the full reload itself. Responses carry loaded_rev.
Deterministic tests for the exact failure sequences: failed reload → no
ack, no generation advance; A-then-B overlap → follower re-runs; matching
rev → coalesces; failed leader → follower re-runs; legacy no-rev callers
keep generation-only coalescing (thread ordering via an instrumented lock,
no sleeps). Client: 6 vitest cases on the ack/retry/in-flight contract.
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