spae-buildlisted

# Build ## When to use - `STATE.json` has `phase: build`. - The work stream needs the next planned task completed. ## Goal - Execute exactly one task from `PLAN.md`, mutating source/tests plus `STATE.json`, while preserving the framework execution cursor. - Complete the active task with minimal production code that meets exhaustive tests, serves its `Intent` and the plan `## Goal`, and leaves seams for downstream tasks. - Meet the task acceptance criteria through exhaustive tests and task verification steps. - Hand off to `/check` for the `done` transition and cursor advance; never claim either. ## Input Read: - `.spae/current/STATE.json` for phase, cursor, and task registry (consult `references/STATE.md` for field reference, directives, and phase snapshots). - `.spae/current/PLAN.md` for the plan `## Goal`, the active task, its `Intent`, acceptance criteria, and verification steps; they carry all the goal context build needs. - Relevant project source, tests, docs, and configuration needed for the active task. ## Testing See `references/testing-guide.md` for test structure, isolation, mocking, assertion, and performance standards. ## Cleanup See `references/cleanup-guide.md` for the self-introduced-artifact checklist and diff-only audit scope. ## Workflow 1. **GATE**—Confirm `.spae/current/STATE.json` has `phase: build` and an active task. Halt on state drift: if `tasks[`active_task_id`]` reads `"done"`, halt; report and make no changes