feat(api): wire /dm/narrate — 200 prose | 502 model_error | 422 invalid log

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

api/app/main.py

@@ -12,6 +12,8 @@ from fastapi.responses import JSONResponse
 from pydantic import BaseModel
 
 from .canon_log import validate_canon_log
+from .narrate import run as narrate_run
+from .ollama_client import ModelError
 
 app = FastAPI(title="coc-rpg proxy", version="0.0.1")
 
@@ -52,7 +54,10 @@ def health() -> dict:
 
 @app.post("/dm/narrate")
 def narrate(req: TurnRequest = Depends(valid_turn)) -> dict:
-    return {"detail": "not implemented"}
+    try:
+        return {"prose": narrate_run(req.canon_log)}
+    except ModelError as exc:
+        raise HTTPException(status_code=502, detail={"model_error": str(exc)})
 
 
 @app.post("/dm/adjudicate")

api/tests/test_narrate_endpoint.py

@@ -0,0 +1,39 @@
+import json
+from pathlib import Path
+
+from fastapi.testclient import TestClient
+
+import app.main as main
+import app.narrate as narrate
+from app.ollama_client import ModelError
+
+client = TestClient(main.app)
+VALID = json.loads((Path(__file__).parent / "fixtures" / "canon_log_valid.json").read_text())
+
+
+def test_valid_log_returns_prose(monkeypatch):
+    monkeypatch.setattr(narrate.ollama_client, "chat", lambda *a, **k: "You stand on the wharf.")
+    monkeypatch.setattr(narrate.call_log, "record", lambda **kw: None)  # keep test output pristine
+    r = client.post("/dm/narrate", json={"canon_log": VALID})
+    assert r.status_code == 200
+    assert r.json() == {"prose": "You stand on the wharf."}
+
+
+def test_model_error_maps_to_502(monkeypatch):
+    def boom(*a, **k):
+        raise ModelError("upstream down")
+
+    monkeypatch.setattr(narrate.ollama_client, "chat", boom)
+    monkeypatch.setattr(narrate.call_log, "record", lambda **kw: None)
+    r = client.post("/dm/narrate", json={"canon_log": VALID})
+    assert r.status_code == 502
+    assert "model_error" in r.json()["detail"]
+
+
+def test_invalid_log_still_422(monkeypatch):
+    monkeypatch.setattr(narrate.ollama_client, "chat", lambda *a, **k: "x")
+    bad = json.loads(json.dumps(VALID))
+    bad["player"]["luck"] = 5  # §7 leak — schema rejects
+    r = client.post("/dm/narrate", json={"canon_log": bad})
+    assert r.status_code == 422
+    assert "canon_log_errors" in r.json()["detail"]