Used downtime while Builder worked its queue to pick up T729 (was on Master's own backlog). TASKGATE.php matched this task to SOP-BACKUP.md, which is a genuine false match (backup file naming, not gov-file suffix conventions) - logged as K237, proceeded on judgment since no real matching SOP exists for this. Wrote systems/governance/SPEC-GOVFILE-SUFFIX.md: documents the real current-state split (WHITELIST=decade, LEGACY=inconsistent per-system, directive/jurisdiction/knowledge/handoff/todo=code, hardcoded in OPEN/CLOSE/CHECKPOINT.php), recommends standardizing the five hardcoded types to decade suffix to match the majority pattern, and lays out a 5-stage migration (dual-read capability first, pilot on Master alone, roll to remaining 10 one at a time - not batched, given the Series M/N fork precedent - then remove the dual-read fallback, then correct ORIENT-REG.md). Explicitly flagged the K217 handoff-write-path fragility and CHECKPOINT's mtime-gate as risks needing extra care in Stage 1. Verified deployed via byte-diff read-back. NOT closing T729 - the spec explicitly says it needs USR369 review/approval before Stage 1 build work starts, closing now would be premature.