M3a review findings 1, 2, 4 and part of 5. One empty log file made brokerd
panic at startup (files[len - 2]); it now opens as an empty log. brokerd's
name check tested one month digit, so a file bxctl ignored could become
brokerd's latest file; both now use proto::is_audit_log_name. Writer no
longer unlinks audit/.lock, which opened a two-writer window. No unwrap in
short_check.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Implemented proto::ChainVerifier as a pure line-holding state machine:
each line is judged only once the next has arrived, so a Recovery record
can mark the line before it not-a-record. Adds ChainFailure, TornTail,
ChainReport, Location and ChainVerifier, wired through lib.rs and the
matching re-export in audit.rs. 13 chain tests pass; make gate prints
gate: ok.
Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)
kyle
