Root cause: after a checkpoint-based snapshot install the engine WAL is empty,
so wal_term_mark() reports tail_term=0. decide_join compares (tail_term, frontier)
lexicographically — tail_term FIRST — so 0 < leader_term classifies the reseeded
shard ReseedRequired on EVERY boot regardless of the correctly-seeded frontier,
re-latching the marker and self-restarting forever. Observed live on tidaldb-2:
30 CrashLoopBackOff restarts, leader tidaldb-1 term 5, baseline=536647, the
frontier seeded correctly (from_seqno=536647) yet the loop persists because the
(tail_term, frontier) compare never reaches the frontier.
Fix 1 (already in tree): seed the post-open frontier from sentinel.snapshot_seq,
not last_wal_seq() (which a checkpoint restore leaves at 0).
Fix 2 (loop-breaker): durably synthesize the artifact's kind-3 TERM_MARKER WAL
record in the post-open reseed seed, at the artifact's captured term + the
reseed-leader region (threaded through an extended 18-byte install sentinel,
back-compat with 10/8-byte). Makes wal_term_mark() truthful on this boot AND
every reboot (blob records are NOT checkpoint-filtered on recovery), so
decide_join returns Clean. Truthful, not a bypass: the artifact IS the leader's
authoritative state at (term, seq); a genuinely-divergent node (no install
sentinel) still surfaces tail_term > term -> Quarantine. Crash-idempotent via a
monotonic-by-term guard.
Fix 3: node-level reseed-restart coordinator — the single process-wide exit fires
once, only after every hosted shard requests a restart or a bounded grace
elapses, so one shard's self-restart never aborts a co-hosted sibling's
in-flight install (S>1). No-op on the S=1 production topology.
Fix 4: is_ready() returns 503 while any reseed marker (SnapshotRequired or
Quarantine) is latched, closing the plain-restart serve-while-behind gap;
readiness is bounded staleness, not "ready the instant the process is up".
Tests: decide_join loop/fix/bounded-reseed unit; install-sentinel 18-byte
round-trip + back-compat; engine durability (term marker survives a checkpoint
advanced past it + crash-reopen); reseed-restart gate (5 cases); reseed_install
carries the term. Verified: cluster_reseed 4/4 (zero-loss rolling restart x2,
quarantine reseed, failover oracle), reseed_install 3/3, m12_reseed_term_marker
4/4, cluster_membership mp_idle/mp_dns/mp_remove x2, tidal-server lib 154/154.
mp_scale_3_5_3 and mp_seed_join_snapshot_catchup OOM on this host (22GB colima
VM); their /health/startup failure is process-down, not the is_ready path Fix 4
touches.
Root-caused and fixed five sharding bugs exposed on the real k3s 3-shard
cluster (rc5→rc7), plus a divergent-rejoin reseed loop found in rc9:
1. reseed shard-awareness (Bug 3, keystone): `run_boot_install_for_region`
visits each hosted group's own shard subdir; per-group leader discovery
appends `?shard=N` so a divergent shard heals from its own leader (not
shard-0's WAL/term — cross-shard contamination).
2. leader self-join term (Bug 4): `become_leader_for_term` now calls
`note_self_won_term` so the elected shard's `joined_term` is set and
`cluster_promote` routes rebalances correctly (was: topology-era mis-read
→ legacy fenced promote → 500).
3. boot self-heal self-pull guard (Bug 2): `leader_shard != my_shard` gate
prevents a node pulling its own stream (its stream isn't a registered peer)
→ eliminates the `PeerUnreachable(self)` loop.
4. scatter-merge degraded partial (Bug 1): failed shard logs + continues
instead of `?`-failing the whole read; bounded read-admission semaphore
(`offload.rs`) sheds as 429 instead of piling into a 36s p99.
5. WAL retention (Bug 5): `compact_wal_retained` keeps `WAL_RETENTION_SEGMENTS=4`
most-recent sealed segments; online path gets the same retention clamp.
Prevents brief-restart forced-reseed.
6. divergent-rejoin reseed loop (Bug 6, rc9): `note_quarantined` latches
`from_seqno = stream_baseline` (not `frontier + 1`) so `wal_covers`
returns `needed=true` and the snapshot installs instead of looping.
Also: `TidalDb::close_shared` for deterministic HNSW save on cluster SIGTERM
(HNSW graph was not saved when request-scoped Arc clones were alive at shutdown);
updated profiling doc with full rc8/rc9 fix narrative; k8s recall job YAMLs.
