major refactor

core/schema/models/checkpoint.py

@@ -0,0 +1,38 @@
+"""Checkpoint schema — source of truth for pipeline state snapshots."""
+
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Any, Dict, Optional
+from uuid import UUID
+
+
+@dataclass
+class Checkpoint:
+    """
+    A snapshot of pipeline state on a timeline.
+
+    Stage outputs stored as JSONB — each stage serializes to JSON,
+    the checkpoint stores it without knowing the shape.
+
+    parent_id forms a tree: multiple children from the same parent
+    = different config tries from the same starting point.
+    """
+
+    id: UUID
+    timeline_id: UUID
+    parent_id: Optional[UUID] = None  # null = root checkpoint
+
+    # Stage outputs — JSONB per stage, opaque to the checkpoint layer
+    stage_outputs: Dict[str, Any] = field(default_factory=dict)
+
+    # Config that produced this checkpoint
+    config_overrides: Dict[str, Any] = field(default_factory=dict)
+
+    # Pipeline state
+    stats: Dict[str, Any] = field(default_factory=dict)
+
+    # Scenario bookmark
+    is_scenario: bool = False
+    scenario_label: str = ""
+
+    created_at: Optional[datetime] = None