Fix Silas identity/voice leak, avatar gender, and add pre-warm batch gen

session.caller was reading name/voice from CALLER_BASES randomized defaults
instead of the slim bg dict — causing Silas to appear as "Earl" with wrong
voice. Now prefers bg data when populated.

Also: avatar endpoint infers gender from voice pool, /api/callers returns bg
name, regulars get canonical voice force-locked, batch gen splits into two
parallel calls with pre-warm so subsequent resets are instant.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/services/caller_gen.py

@@ -92,6 +92,7 @@ def build_batch_prompt(ctx: dict) -> str:
             lines.append(f"Current arc state: {r['arc_state']}")
             lines.append("")
             lines.append(f"For {r['name']}: invent a fresh reason he is calling tonight — a new development, grievance, or specific recent event. DO NOT alter his voice, personality, or core traits. Write a new scene for an existing character.")
+            lines.append(f"CRITICAL — this caller MUST appear in the output JSON with EXACTLY these fields locked: name=\"{r['name']}\", voice_suggestion=\"{r['voice']}\", age={r['age']}. Do NOT rename this caller. Do NOT give him a different voice. Do NOT change his age. Only invent: location, identity, situation, reason_calling, opening_line, secret_want, specific_details, emotional_register.")
             lines.append("")
 
     lines.append(f"Available voices (voice_suggestion must match one of these exactly):")
@@ -131,3 +132,54 @@ async def generate_batch(ctx: dict) -> list[CallerIdentity]:
     for c in callers:
         c.voice_resolved = resolve_voice(c.voice_suggestion, ctx["voice_roster"])
     return callers
+
+
+REGULAR_SYSTEM_PROMPT = """You are writing a single caller — a recurring character on Luke's late-night radio show. The character's identity is fixed (name, voice, age, core lore). You only invent a fresh reason he's calling tonight, grounded in his current arc state.
+
+Output strict JSON with these fields only: location, identity, situation, reason_calling, opening_line, secret_want, specific_details (array of 2-3 strings), emotional_register. Do NOT include name, voice_suggestion, or age — those are locked."""
+
+
+async def generate_regular_situation(regular: dict, ctx: dict) -> dict:
+    """Generate a fresh situation for a locked regular. Returns a dict matching
+    the CallerIdentity schema. One small LLM call (~$0.01)."""
+    lines = [
+        f"Tonight is {ctx['date']}. {ctx['weather']}.",
+        "",
+        f"### {regular['name']}",
+        regular["lore"],
+        f"Current arc state: {regular['arc_state']}",
+        "",
+        f"Invent a fresh reason {regular['name']} is calling tonight — a new development, grievance, or specific recent event. DO NOT alter his voice, personality, or core traits.",
+        "",
+        "Output JSON only, no prose.",
+    ]
+    prompt = REGULAR_SYSTEM_PROMPT + "\n\n" + "\n".join(lines)
+
+    async with httpx.AsyncClient(timeout=60.0) as client:
+        resp = await client.post(
+            "https://openrouter.ai/api/v1/chat/completions",
+            headers={"Authorization": f"Bearer {settings.openrouter_api_key}"},
+            json={
+                "model": BATCH_MODEL,
+                "messages": [{"role": "user", "content": prompt}],
+                "response_format": {"type": "json_object"},
+                "max_tokens": 1500,
+                "temperature": 0.9,
+            },
+        )
+        resp.raise_for_status()
+        data = resp.json()
+
+    content = data["choices"][0]["message"]["content"]
+    usage = data.get("usage", {})
+    cost_tracker.record_llm_call(
+        category="background_gen",
+        model=BATCH_MODEL,
+        usage_data=usage,
+    )
+
+    stripped = content.strip()
+    if stripped.startswith("```") and stripped.endswith("```"):
+        lines = stripped.splitlines()
+        stripped = "\n".join(lines[1:-1])
+    return json.loads(stripped)