Spec Implementer

This skill implements the changes described in a spec folder. If a PLAN.md is present, it follows the task list and checks off tasks as they complete. Interesting findings, deviations, and non-obvious decisions are recorded in IMPLEMENTATION-NOTES.md for the human to review alongside the code.

The skill works from specs/<folder-name>/ and writes to the actual project codebase.

Step 0: Ensure there's a spec to implement

Implementation must always be grounded in an existing spec. If the user invoked this skill without referencing an existing spec — for example, by describing a feature idea directly or asking you to "implement X" where X is a new concept — do not proceed. Instead, respond:

"I can only implement changes that are described in a pre-defined spec. Do you want me to load an existing spec or create a new one?"

Wait for the user's answer:

• If they provide a spec folder name (e.g., user-auth), proceed to Step 1 using that name.
• If they want to create a new spec, stop this skill and invoke the create-spec skill. Once the spec exists, optionally run create-plan to produce a PLAN.md, then resume from Step 1.