Agent Skills: log-build

Add or refine sparse, structured, file-persisted application logs for non-trivial code changes. Use when Agent is proposing an implementation approach, writing a plan, or implementing or modifying complex business logic, critical state transitions, validation or parsing flows, boundary interactions (HTTP, DB, cache, queue, filesystem, subprocess), retries, fallbacks, async jobs, concurrency, or background tasks, because planning is the right time to decide log placement. Reuse the project's existing logging infrastructure whenever possible. Do not use for trivial edits, simple obvious CRUD, blanket "log everything" requests, or low-value noise.