6.3: Fix single-node bug — ha_compute_safe_committed_lsn now returns
self_lsn instead of 0 for n_peers=0 (prevents WAL truncation on
single-node re-election). Add self_lsn/self_tag to ha_elect_ctx_t,
populated unconditionally in ha_start_election_async. All 3 test
scenarios pass under ASAN.
6.4: Add test_snapshot_recv_128kb_two_chunks (128KB snapshot in
2x64KB chunks, verifies size and applied_lsn); 4 other test cases
already existed from tasks 3.5c/3.5d. All ASAN-clean.
- Change HA_DEFAULT_COMMITTING_TIMEOUT_MS from 10000 to 60000
- committing_timeout_fn: count converged/pending standbys from
standby_converged[], log WARN with counts, then promote (degraded mode)
- Replace hardcoded 10000 in test_ha_evaluate_committing.c with macro
- Three new tests: default=60000, degrade-promote with 1/2 and 0/2 converged
- In raft_cb_become_leader, after persist_truncate_wal_above(safe_lsn),
store safe_lsn to ha->last_known_committed_lsn via atomic release
- Test: 3-node voters [100,150,200] → safe_lsn=150; asserts
ha->last_known_committed_lsn == 150 after raft_cb_become_leader_for_test