feat(ce-plan): add U-IDs and origin trace to plan template (#632)

plugins/compound-engineering/skills/ce-work/SKILL.md

@@ -114,6 +114,7 @@ Determine how to proceed based on what was provided in `<input_document>`.
 3. **Create Todo List** _(skip if Phase 0 already built one, or if Phase 0 routed as Trivial)_
    - Use your available task tracking tool (e.g., TodoWrite, task lists) to break the plan into actionable tasks
    - Derive tasks from the plan's implementation units, dependencies, files, test targets, and verification criteria
+   - When the plan defines U-IDs for Implementation Units, preserve the unit's U-ID as a prefix in the task subject (e.g., "U3: Add parser coverage"). This keeps blocker references, deferred-work notes, and final summaries anchored to the same identifier the plan uses, so progress and traceability remain unambiguous across plan edits
    - Carry each unit's `Execution note` into the task when present
    - For each unit, read the `Patterns to follow` field before implementing — these point to specific files or conventions to mirror
    - Use each unit's `Verification` field as the primary "done" signal for that task
@@ -294,7 +295,7 @@ Determine how to proceed based on what was provided in `<input_document>`.
    - Note any blockers or unexpected discoveries
    - Create new tasks if scope expands
    - Keep user informed of major milestones
-   - When the plan or origin document carries stable R-IDs (and optionally A/F/AE IDs), reference them in blockers, deferred-work notes, task summaries, and final verification — not routine status updates. This preserves traceability back to requirements without burying signal under noise.
+   - When the plan defines U-IDs for Implementation Units, or the plan or origin document carries stable R-IDs (and optionally A/F/AE IDs), reference them in blockers, deferred-work notes, task summaries, and final verification — not routine status updates. U-IDs anchor units across plan edits; R/A/F/AE anchor product intent across the brainstorm-plan handoff. Use the IDs the plan supplies and do not invent ones it does not. This preserves traceability without burying signal under noise.
 
 ### Phase 3-4: Quality Check and Ship It