spec-implement

# Spec Implement Execute the approved Spec-backed Plan. Track progress when it uses tracked tasks. Report. Stop when blocked. **Announce at start:** "I'm using the spec-implement skill to execute this plan." This skill does not make design decisions or change approved content. It may persist approved content from the conversation when Plan Mode could not write the required artifact. If the plan is wrong, go back to spec-plan. If the design is wrong, go back to spec-brainstorm. ## Prerequisites Resolve required artifacts in order before starting product implementation: 1. If `docs/specs/YYYY-MM-DD-<feature>/design.md` is missing, write it from the approved design in the current conversation. Validate the file, report its path, and stop. Do not create `plan.json` or start implementation in the same invocation. 2. Otherwise, if `docs/specs/YYYY-MM-DD-<feature>/plan.json` is missing, write it from the approved plan in the current conversation. Validate it against the schema in `spec-plan`, report its path, and stop. Do not start implementation in the same invocation. 3. If the approved content needed for the next missing artifact is not available in the current conversation, stop and tell the human what content is unavailable. Do not ask the human to create the file. 4. When both artifacts exist, verify that any tracker entries selected during planning are available, along with `docs/agents/issue-tracker.md` when tracking is configured. 5. Verify that y...