feat(api): narrate service — render→route→call→log, returns raw prose

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

api/app/narrate.py

@@ -0,0 +1,37 @@
+"""The Narrator role service (charter §5). Renders the digest, routes the model,
+calls Ollama with one retry, logs the call (§10), and returns raw prose — tags
+left intact for the client's TagExtractor to harvest (§2/§6). Raises ModelError
+on failure for the handler to map to a 502.
+"""
+
+import random
+from time import perf_counter
+
+from . import call_log, ollama_client, prompts, routing
+
+
+def run(canon_log: dict) -> str:
+    cfg = routing.for_role("narrator")
+    options = {**cfg.options, "seed": random.randint(0, 2**31 - 1)}
+    messages = [
+        {"role": "system", "content": prompts.system_prompt("narrator")},
+        {"role": "user", "content": prompts.render_digest(canon_log)},
+    ]
+
+    start = perf_counter()
+    try:
+        text = ollama_client.chat(cfg.model, messages, options, think=cfg.think)
+    except ollama_client.ModelError as exc:
+        call_log.record(
+            role="narrator", model=cfg.model, options=options, messages=messages,
+            canon_log=canon_log, ok=False,
+            latency_ms=int((perf_counter() - start) * 1000), error=str(exc),
+        )
+        raise
+
+    call_log.record(
+        role="narrator", model=cfg.model, options=options, messages=messages,
+        canon_log=canon_log, ok=True,
+        latency_ms=int((perf_counter() - start) * 1000), response=text,
+    )
+    return text