feat: she can suggest + switch modes (set_mode tool + mode awareness)

"She suggests, you confirm" — instead of brittle keyword→mode mapping, she's given
awareness of her modes + the ability to switch, and her judgment decides when to
offer (the model reads "should I drive to Cleveland?" vs "should I fold the river"
far better than a lexicon could).

- tools: set_mode(mode) — switches the session's mode; in _BASE (all modes).
- mind: a per-turn mode-menu note listing her modes + "offer a switch when the work
  clearly shifts; on his yes, call set_mode; don't nag."
- Sticky mode stays manual otherwise; Poker still auto-engages on session start.
- test: set_mode switches + rejects unknown. Suite 97 green, ruff clean.

Note: server-side switch takes effect next turn; the UI badge syncs on next mode
load (cosmetic lag).

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

lyra/tools.py

@@ -52,6 +52,20 @@ def _think_about(args: dict, ctx: dict) -> str:
             "I'll come back to it on my own between our conversations.")
 
 
+def _set_mode(args: dict, ctx: dict) -> str:
+    from lyra import modes
+    key = (args.get("mode") or "").strip().lower()
+    m = modes.MODES.get(key)
+    if not m:
+        return f"(unknown mode '{key}'; valid: {', '.join(modes.MODES)})"
+    sid = ctx.get("session_id")
+    if not sid:
+        return "(no session to switch)"
+    memory.set_session_mode(sid, key)
+    logbus.log("info", "mode switch (tool)", session=sid, mode=key)
+    return f"Switched to {m.label} mode."
+
+
 def _thought_response(args: dict, ctx: dict) -> str:
     try:
         tid = int(args.get("thread_id"))
@@ -452,6 +466,12 @@ _S = {"type": "string"}
 _N = {"type": "number"}
 
 TOOLS.update({
+    "set_mode": {"handler": _set_mode, "spec": _f(
+        "set_mode",
+        "Switch your conversation mode when the work clearly shifts and Brian's agreed to it. "
+        "Offer first ('want me in Decide for this?'), then call this on his yes.",
+        {"mode": {**_S, "description": "Mode key: conversation | poker_cash | build | explore | study | decide"}},
+        ["mode"])},
     "thought_response": {"handler": _thought_response, "spec": _f(
         "thought_response",
         "When you've brought one of your own thoughts/threads to Brian and he responds to "