Implement code based on the change artifacts. Supports two modes:

Gherkin-driven (default): feature files drive implementation and testing
Proposal-driven: when gherkin is skipped (technical changes), proposal drives testing

<decision_boundary>

Use for:

Implementing code for a Beat change that has spec artifacts (gherkin or proposal) done
TDD implementation driven by feature files or proposal risk points
Resuming implementation of a partially completed change

NOT for:

Creating spec artifacts like proposal, gherkin, or design.md (use /beat:design)
Breaking down tasks or creating execution plans (use /beat:plan)
Verifying implementation completeness (use /beat:verify)
Exploring ideas or investigating a problem (use /beat:explore)

apply