# Retrospective phase implementation

Added explicit final `retrospective` phase to the deterministic task-phase machine.

## Changes
- phase model now includes:
  - `retrospective`
  - `closed`
- `closed` is now the only fully terminal phase
- `done`, `blocked`, and `needs_user_decision` can flow into `retrospective`
- retrospective cannot repair the main deliverable; it must create follow-up tasks instead
- runner now enforces retrospective completion before `retrospective -> closed`
- init now creates `RETROSPECTIVE.md`
- state schema now tracks:
  - `Retrospective required`
  - `Retrospective status`
  - `Preventive changes needed`
  - `Observed failures summary`
  - `Observed failures`
  - `Preventive changes proposed`
  - `Follow-up tasks created`

## Validation
- `bun run typecheck` passes
- `task-phase-init` smoke test created the new retrospective artifacts successfully

## Effect
The phase machine can now end with a deterministic learning tail that captures failure modes and spawns follow-up tasks without inflating or reopening the original task.