Implement Task

Implement one task per invocation and update that task's result. Do not close the milestone.

Preconditions

1. Identify exactly one task. If the user asks for the next task, scan docs/planning/tasks/ and choose one ready task whose blocked_by tasks are completed.
2. Read docs/specifications/product.md, the task, associated milestone, linked supporting requirements, applicable ADRs, nearest AGENTS.md, and CONTEXT.md if present.
3. Verify every blocked_by task is completed; refuse blocked tasks and explain the blockers.
4. Refuse cancelled tasks. Surface ambiguity or conflicts before editing.
5. Set status to in-progress only when work can actually begin, preserving existing manual content.

Implementation loop