syncStateFrontmatter() rebuilds YAML frontmatter from the body on every
writeStateMd() call. If an agent removes or omits the Status: field from
the body, buildStateFrontmatter() defaults to 'unknown', overwriting a
previously valid status (e.g., 'executing').
Fix: read existing frontmatter before stripping, and preserve its status
value when the body-derived status would be 'unknown'. This makes
frontmatter self-healing — once a status is set, it persists even if the
body loses the field.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
f850952332