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fix(controller): restored-but-stale raft term permanently blocked re-election after restart (bug-1695)

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Found via the mandatory live HA chaotic soak for this session's controller
audit campaign -- unrelated to any of the 9 audit fixes (bug-1684/1687/
1689/1690/1691/1692/1693/1694), all in ha.c/persist.c/job.c/cluster.c/
sched.c/worker.c; this is in myapp.c, untouched by any of them.

myapp_run()'s bootstrap "is a leader already known" check had a fallback
`c.ha.raft.term > 0` meant to detect genuine new raft activity processed
during the startup-stagger nap. But ha_restore_term() loads ha->term from
disk BEFORE this check runs, on every boot -- and Raft terms only ever
increase, never reset. So `raft.term > 0` is trivially true on every
restart for the rest of the cluster's on-disk lifetime, once it has ever
held one election, regardless of whether any leader is currently
reachable. Live-reproduced: every node, on every restart after the
cluster's first election, unconditionally skipped ha_start_election_async
forever -- no node could ever re-assert leadership through a real
election again. bug-1477's existing cluster_init_phase2 retry loop kept
firing correctly (confirmed in the reproduction logs) but could never
succeed, since the deeper cause -- no election ever runs to produce a
live primary to push config from -- was never addressed by that fix.

Fixed by snapshotting `term_at_boot` right after ha_restore_term()/
ha_init_raft() seed the term, strictly before the stagger nap, and
comparing `raft.term > term_at_boot` instead of `raft.term > 0` -- only a
term that has genuinely ADVANCED during this boot cycle (real vote/
heartbeat traffic processed) counts as evidence a leader is known. The
decision was extracted into a new, unit-testable myapp_leader_already_known()
(startup_validation.c, since controller_unit_test deliberately excludes
myapp.c/main.c). voted_for_name/vft==cur and primary_ctrl_fd>=0 checks
are unchanged.

7 new tests in test_ha_startup.c; RED/GREEN independently verified.
Rigorous A/B live-soak proof (identical 6-round --chaotic run, fixed vs
git-stashed-back-to-original): baseline showed term frozen for the whole
run and zero election activity on any non-primary node; fixed run showed
term genuinely progressing and ctrl-2 achieving a real, log-verified
CTRL_PRIMARY transition via a won PreVote round -- proof a node other
than the original primary can now take over, which was structurally
impossible before. Full controller suite: 1191 tests, 2 failures -- both
the pre-existing, unrelated bug-1561 overlayfs sandbox flake.

Residual, NOT independently verified yet (flagged honestly, not fixed
here): the fixed run's chaotic verdict showed committed_job_loss=6
(baseline 0) -- traced via waldump to one jobid missing from every node's
WAL, at the cold-boot window before round 1. Resembles the already-fixed
bug-1487 false-positive class (apply-pump-lag racing verify_classify's
expect-job check) but the reported mechanism doesn't perfectly match
(bug-1487's job was present-in-WAL/not-yet-visible; this one is described
as absent from every WAL entirely) -- needs independent re-verification
before being dismissed, tracked as a follow-up.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AgYRU3zDTqNGV5Jk8aiKLg
This commit is contained in:
Rongsong Shen 2026-08-25 16:11:37 +00:00
parent 23c5c26a23
commit ac46bfa649
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4 changed files with 792 additions and 444 deletions
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