implement - Implementation Stage

Invariants

Require an approved task document before changing implementation files.
Treat the task document as the primary scope contract.
Do not broaden scope without user approval.
Do not rely on provider-specific model switch commands.
implement auto is the only automation entry point.
Do not start while the task doc lists a BLOCKING open decision. Stop and ask the user, quoting the decision and its options.
If the project's AGENTS.md defines its own claim or tracker convention (for example "the pushed branch is the claim; don't edit TASKS.md at start"), follow it instead of the tracker moves below.
Update TASKS.md at both transitions (Planned → In Progress on start, In Progress → Testing on finish) and re-read the tracker before handoff to confirm the row moved. A stale tracker blocks downstream and headless sessions.

Runtime adapters may expose this stage as a slash command, menu action, or natural-language skill invocation. The portable stage name is implement.