feat(api): origin seed JSON Schema + validator

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/tests/test_origin_schema.py

@@ -0,0 +1,48 @@
+import copy
+
+from app.canon_log import validate_origin
+
+VALID_ORIGIN = {
+    "schema_version": 1,
+    "id": "deserter",
+    "display_name": "The Deserter",
+    "description": "You walked away from a company that doesn't allow walking away.",
+    "start_location_id": "greywater_docks",
+    "situation": ["Arrived at Greywater by barge before dawn, hood up"],
+    "opening_facts": ["the player deserted the Iron Kettle mercenary company"],
+    "disposition_overrides": {"brannoc_thane": 40, "cadwyn_vell": 15},
+    "inventory_grants": [{"item_id": "worn_shortsword", "qty": 1}],
+    "start_quest_id": "find_the_ledger",
+    "build_constraints": {
+        "allowed_classes": ["sellsword", "assassin", "priest"],
+        "luck_modifier": 0,
+    },
+}
+
+
+def test_valid_origin_passes():
+    assert validate_origin(VALID_ORIGIN) == []
+
+
+def test_null_start_quest_is_allowed():
+    doc = copy.deepcopy(VALID_ORIGIN)
+    doc["start_quest_id"] = None
+    assert validate_origin(doc) == []
+
+
+def test_unknown_class_is_rejected():
+    doc = copy.deepcopy(VALID_ORIGIN)
+    doc["build_constraints"]["allowed_classes"] = ["bard"]
+    assert validate_origin(doc) != []
+
+
+def test_missing_required_field_is_rejected():
+    doc = copy.deepcopy(VALID_ORIGIN)
+    del doc["start_location_id"]
+    assert validate_origin(doc) != []
+
+
+def test_extra_field_is_rejected():
+    doc = copy.deepcopy(VALID_ORIGIN)
+    doc["surprise"] = True
+    assert validate_origin(doc) != []