backlot phase 0: artifact contract + gate hardening
- init_project() writes project.json marker + canonical workspace layout
- write_checkpoint enforces approval gates: completed on a gated stage
requires human_approved=True (GATE VIOLATION otherwise)
- superseded checkpoints archived to projects/<id>/history/ (stage
versioning, gate audit trail, replay)
- BaseTool auto-instruments execute() -> projects/<id>/events.jsonl
(start/finish/error, scene_id, cost) for the Backlot live board
- assets stage now gates (human_approval_default: true) in all manifests
- checkpoint-protocol + AGENT_GUIDE: manifest gate value is binding,
awaiting_human + end-turn protocol, per-gate approval, canonical
checkpoint location fixed to projects/<id>/
- gate reminder footer on all gating stage director skills
- /backlot command files for Claude Code, Codex, Cursor, Copilot
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