feat(P3): mind/mouth split — separate voice model for the final reply (seam, default off)

The mind (chat backend/model) decides, reasons, and runs tools → a draft; the mouth
re-voices that draft in her character. Default: no mouth configured → the mind's
draft IS the reply, bit-for-bit the old behavior (and old streaming path untouched).

- config: MOUTH_BACKEND / MOUTH_MODEL. The slot for an eventual fine-tuned voice.
- chat: _mind_loop (tool/generation loop, non-stream, returns draft + tools_run),
  _voice_pass / mind.voice_messages (re-voice the draft, keep every fact/number),
  _mouth_target (active only when configured AND != mind). respond + respond_stream
  branch: mouth off = stream the mind directly (unchanged); mouth on = mind decides
  + runs tools, then the mouth streams the re-voiced reply. Falls back to the draft
  on any mouth failure (chat never breaks).
- Key payoff: the mouth needs no tool support (the mind handles tools), so it can be
  a non-tool character model (Dolphin / Claude / fine-tune). Makes the fine-tune
  easy: teach a small model to *sound* like Lyra, not to be smart.
- tests: mouth target on/off, voice_messages shape, voice_pass revoice+fallback.
  Suite 96 green, ruff clean.

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

lyra/config.py

@@ -38,6 +38,11 @@ class Config:
     ping_quiet_hours: str  # local "start-end" 24h window to stay silent, e.g. "1-9"
     digest_hour: int       # local hour (0-23) to send her daily "what I've been thinking" digest
     chat_deliberate: bool  # think privately before answering substantive chat turns
+    # Mind/mouth split: the mind (the chat backend/model above) decides, reasons, and
+    # runs tools; the mouth re-voices the final reply in her character. Empty = mouth
+    # is the mind (no separate pass) — the slot for an eventual fine-tuned voice.
+    mouth_backend: str
+    mouth_model: str | None
     # External input feed (her #1: react to the world). Comma-separated RSS/Atom URLs.
     feeds: tuple[str, ...]
     feed_react_prob: float  # chance a would-be new thread reacts to a feed item instead
@@ -81,6 +86,8 @@ def load() -> Config:
         ping_quiet_hours=os.getenv("PING_QUIET_HOURS", "1-9"),
         digest_hour=int(os.getenv("DIGEST_HOUR", "18")),
         chat_deliberate=os.getenv("CHAT_DELIBERATE", "true").lower() not in ("0", "false", "no"),
+        mouth_backend=os.getenv("MOUTH_BACKEND", "").lower(),
+        mouth_model=os.getenv("MOUTH_MODEL") or None,
         feeds=_csv("LYRA_FEEDS", "https://hnrss.org/frontpage,https://www.pokernews.com/rss.php"),
         feed_react_prob=float(os.getenv("FEED_REACT_PROB", "0.5")),
     )