zeekay e08dba1faa fix(mpc): /healthz reports quorum — not all-peers-ready (P0-1) ...

Survivor nodes in a t-of-n ensemble now report healthy so long as they
still have enough ready peers (including self) to form a signing quorum
for their configured threshold. Previously, ArePeersReady() was the gate
and any single peer loss collapsed availability on the remaining nodes.

Repro (Scientist, 2026-04-20): scale liquid-mpc-mpc-node StatefulSet
from 3 → 2 replicas in the liquidity devnet; surviving pods returned HTTP
503 with log "Peers not ready expected=3 ready=2" even though 2 nodes
are sufficient for the 2-of-3 (threshold=1) signing quorum.

Fix:

- pkg/transport/registry.go: add HasSigningQuorum(threshold) which returns
  true when readyCount >= threshold+1 (the CGGMP21/FROST signers-required
  count used everywhere in pkg/mpc/node.go).
- pkg/mpc/registry.go: matching method on the legacy Consul-backed
  registry plus interface addition to PeerRegistry.
- cmd/mpcd/main.go: /healthz handler switched to HasSigningQuorum(threshold)
  for the 200/503 gate. ArePeersReady() is still reported in the JSON
  body (as `ready`) for observability. `status` becomes
  "healthy" / "healthy-reduced" / "degraded" so operators can see the
  in-between state.
- cmd/mpcd/main.go: ConsensusPeerRegistry wrapper delegates the new
  method to the underlying transport registry.

Keygen sessions deliberately continue to require ArePeersReady() — a
fresh wallet still needs every participant present. Only the /healthz
gate is relaxed, which matches the availability story for signing.

Tests: pkg/transport/registry_test.go covers
- Test_HasSigningQuorum_3Node_2of3 (the Scientist repro — survivors
  still quorum-ok after one peer loss)
- Test_HasSigningQuorum_5Node_3of5 (larger ensemble, f=2 tolerance)
- Test_HasSigningQuorum_ArePeersReady_Decoupled (the two APIs do not
  gate each other)
- Test_HasSigningQuorum_BoundaryCheck (pins arithmetic: required =
  threshold+1, not threshold)

All 11 test cases pass; transport + mpc package suites clean.

2026-04-20 18:48:31 -07:00

..

main.go

fix(mpc): /healthz reports quorum — not all-peers-ready (P0-1)

2026-04-20 18:48:31 -07:00