feat(api): §10 JSON-lines call logging (full prompt + seed, injectable sink)

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

api/tests/test_call_log.py

@@ -0,0 +1,34 @@
+import json
+
+from app.call_log import record
+
+
+def test_success_record_shape():
+    captured = []
+    rec = record(
+        role="narrator", model="qwen3.5:latest", options={"seed": 7},
+        messages=[{"role": "user", "content": "x"}], canon_log={"a": 1},
+        ok=True, latency_ms=120, response="prose", write=captured.append,
+    )
+    assert len(captured) == 1
+    parsed = json.loads(captured[0])
+    assert parsed["ok"] is True
+    assert parsed["response"] == "prose"
+    assert parsed["options"]["seed"] == 7
+    assert parsed["role"] == "narrator"
+    assert parsed["canon_log"] == {"a": 1}
+    assert "error" not in parsed
+    assert "ts" in parsed
+    assert rec["response"] == "prose"
+
+
+def test_failure_record_shape():
+    captured = []
+    record(
+        role="narrator", model="m", options={}, messages=[], canon_log={},
+        ok=False, latency_ms=5, error="ModelError: down", write=captured.append,
+    )
+    parsed = json.loads(captured[0])
+    assert parsed["ok"] is False
+    assert parsed["error"] == "ModelError: down"
+    assert "response" not in parsed