Six-task checkpoint hardening the promotion and failover paths:
T1: 4-gate candidate evaluation (heartbeat freshness, WAL lag, role,
server liveness) with structured rejection reasons.
T2: Orphaned-primary re-evaluation on replica reconnect (B-06/B-08).
T3: Deferred timer safety — epoch validation prevents stale timers
from firing on recreated/changed volumes (B-07).
T4: Rebuild addr cleanup on promotion (B-11), NVMe publication
refresh on heartbeat, and preflight endpoint wiring.
T5: Manual promote API — POST /block/volume/{name}/promote with
force flag, target server selection, and structured rejection
response. Shared applyPromotionLocked/finalizePromotion helpers
eliminate duplication between auto and manual paths.
T6: Read-only preflight endpoint (GET /block/volume/{name}/preflight)
and blockapi client wrappers (Preflight, Promote).
BUG-T5-1: PromotionsTotal counter moved to finalizePromotion (shared
by both auto and manual paths) to prevent metrics divergence.
24 files changed, ~6500 lines added. 42 new QA adversarial tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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