feat(units): add last_updated timestamp to unit frontmatter

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jwaldrip

plugin/lib/dag.sh

@@ -6,6 +6,7 @@
 # status: pending  # pending | in_progress | completed | blocked
 # depends_on: [unit-01-setup, unit-03-session]
 # branch: ai-dlc/intent/04-auth
+# last_updated: 2026-03-26T19:30:00Z  # ISO 8601 UTC timestamp of last status change
 # ---
 
 # Source configuration system
@@ -480,6 +481,9 @@ update_unit_status() {
 
   # Update status in frontmatter using han parse yaml-set
   han parse yaml-set status "$new_status" < "$unit_file" > "$unit_file.tmp" && mv "$unit_file.tmp" "$unit_file"
+
+  # Update last_updated timestamp
+  han parse yaml-set last_updated "$(date -u +%Y-%m-%dT%H:%M:%SZ)" < "$unit_file" > "$unit_file.tmp" && mv "$unit_file.tmp" "$unit_file"
 }
 
 # Get DAG summary counts

plugin/skills/elaborate/SKILL.md

@@ -977,6 +977,7 @@ git commit -m "elaborate(${INTENT_SLUG}): define intent"
 ```markdown
 ---
 status: pending
+last_updated: ""  # ISO 8601 UTC timestamp of last status change (auto-populated)
 depends_on: []
 branch: ai-dlc/{intent-slug}/NN-{unit-slug}
 discipline: {discipline}  # frontend, backend, api, documentation, devops, design, etc.