feat(music-lab): pipeline 상태 머신

music-lab/app/pipeline/state_machine.py

@@ -0,0 +1,41 @@
+"""파이프라인 상태 머신 — 전이 규칙 단일 소스."""
+
+STEPS = ["cover", "video", "thumb", "meta", "review", "publish"]
+USER_GATES = ["cover", "video", "thumb", "meta", "publish"]  # review는 자동
+
+_APPROVE_NEXT = {
+    "cover_pending":   "video_pending",
+    "video_pending":   "thumb_pending",
+    "thumb_pending":   "meta_pending",
+    "meta_pending":    "ai_review",      # 자동 검토 단계로
+    "publish_pending": "publishing",
+}
+
+TERMINAL_STATES = {"published", "cancelled", "failed", "awaiting_manual"}
+
+
+def next_state_on_approve(state: str) -> str:
+    if state not in _APPROVE_NEXT:
+        raise ValueError(f"승인 불가 상태: {state}")
+    return _APPROVE_NEXT[state]
+
+
+def next_state_on_reject(state: str) -> str:
+    if not state.endswith("_pending"):
+        raise ValueError(f"반려 불가 상태: {state}")
+    return state  # 같은 상태 유지 (재생성 후 다시 _pending)
+
+
+def can_transition(from_state: str, to_state: str) -> bool:
+    if from_state in TERMINAL_STATES:
+        return False
+    if to_state in {"cancelled", "failed", "awaiting_manual"}:
+        return True
+    if to_state == _APPROVE_NEXT.get(from_state):
+        return True
+    # 자동 전이 (ai_review → publish_pending, publishing → published)
+    auto_transitions = {
+        ("ai_review", "publish_pending"),
+        ("publishing", "published"),
+    }
+    return (from_state, to_state) in auto_transitions