feat: couple broadcast to voice + voice-controlled broadcast toggle

Completes the STREAM_BROWSER=true behaviour:
- handleJoin auto-starts the broadcast on voice join and wires the session to
  the guild streamer; each turn reports the live state to the brain so search
  routes Chrome (live) vs Gemini (off).
- New setBroadcast tool lets the user toggle the broadcast by voice ("방송
  켜줘/꺼줘") via the LLM (no hardcoded phrases); it refuses when
  STREAM_BROWSER=false. The directive flows brain -> bridge (broadcast_action)
  -> bot streamer.start/stop, guarded by isActive() so it's idempotent.
- Per-turn IPC uses a thread-local (reply/turn_state.py) instead of threading
  params through the whole engine chain: bridge sets broadcasting in, tool
  records the directive out; Tool.execute exposes broadcasting on ToolContext.

Bot typecheck clean; brain covered by tests/test_set_broadcast.py (+ existing
routing tests). Specs + docs updated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/jarvis/tools/builtin/set_broadcast.py

@@ -0,0 +1,75 @@
+"""Start or stop the live screen-share broadcast (Go-Live) on request.
+
+The brain cannot drive the Discord broadcast itself — the bot owns it. This
+tool records a directive ("start"/"stop") in the per-turn state; the bridge
+returns it to the bot, which performs the actual start/stop. Only meaningful in
+screen-share mode (``STREAM_BROWSER`` true); when broadcasting is disabled the
+tool refuses so the user is told it cannot be turned on.
+"""
+
+from __future__ import annotations
+
+from typing import Dict, Any, Optional
+
+from ..base import Tool, ToolContext
+from ..types import ToolExecutionResult
+from ...debug import debug_log
+
+
+class SetBroadcastTool(Tool):
+    """Turn the live screen-share broadcast on or off."""
+
+    @property
+    def name(self) -> str:
+        return "setBroadcast"
+
+    @property
+    def description(self) -> str:
+        return (
+            "Start or stop the live screen-share broadcast (Go-Live / showing your "
+            "screen on the call). Use when the user asks to turn the broadcast or "
+            "screen on or off (show/hide your screen, go live, stop streaming). "
+            "Only available in screen-share mode."
+        )
+
+    @property
+    def inputSchema(self) -> Dict[str, Any]:
+        return {
+            "type": "object",
+            "properties": {
+                "action": {
+                    "type": "string",
+                    "enum": ["start", "stop"],
+                    "description": "'start' to begin the broadcast, 'stop' to end it.",
+                }
+            },
+            "required": ["action"],
+        }
+
+    def run(self, args: Optional[Dict[str, Any]], context: ToolContext) -> ToolExecutionResult:
+        cfg = context.cfg
+        if not getattr(cfg, "stream_browser", True):
+            # Broadcast capability is disabled (STREAM_BROWSER=false): refuse so
+            # the user is clearly told it can't be turned on in this mode.
+            return ToolExecutionResult(
+                success=False,
+                reply_text="방송(화면 공유) 기능이 꺼져 있어 켤 수 없습니다 (STREAM_BROWSER=false).",
+            )
+
+        action = ""
+        if args and isinstance(args, dict):
+            action = str(args.get("action", "")).strip().lower()
+        if action not in ("start", "stop"):
+            return ToolExecutionResult(
+                success=False,
+                reply_text="Specify action='start' or action='stop'.",
+            )
+
+        # Record the directive for the bridge to return to the bot.
+        from ...reply.turn_state import request_broadcast
+        request_broadcast(action)
+        debug_log(f"    📡 setBroadcast requested: {action}", "stream")
+        return ToolExecutionResult(
+            success=True,
+            reply_text="방송을 시작합니다." if action == "start" else "방송을 종료합니다.",
+        )

src/jarvis/tools/builtin/set_broadcast.spec.md

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+# setBroadcast tool
+
+Lets the user turn the live screen-share broadcast (Go-Live) on or off by voice
+or text, e.g. "방송 켜줘 / 화면 보여줘" or "방송 꺼줘". The LLM picks the intent
+and calls the tool (no hardcoded phrase matching), so it works in any language.
+
+## Contract
+
+- Input: `{ "action": "start" | "stop" }`.
+- The brain cannot drive the Discord broadcast itself (the bot owns it). The
+  tool records the directive in request-scoped state
+  (`jarvis/reply/turn_state.request_broadcast`); `bridge/server.py` returns it as
+  `broadcast_action` in the `/converse` (and `/text`) response, and the bot
+  (`voice.ts` -> `index.ts` `onBroadcastAction`) calls `streamer.start/stop`.
+- Mode gate: when `cfg.stream_browser` is false (`STREAM_BROWSER=false`)
+  broadcasting is disabled — the tool refuses with a spoken explanation and
+  records no directive. This is the same capability flag that makes `/stream`
+  refuse and forces real-time search to Gemini.
+
+## Principles
+
+- Tool returns raw intent/result; it performs no broadcast itself and makes no
+  LLM call.
+- Idempotent at the bot edge: `start` is a no-op if already live, `stop` a no-op
+  if already off (`streamer.isActive()` guard).
+- Fail-safe: a missing/invalid action records nothing; the bot only acts on an
+  explicit `"start"`/`"stop"` directive.
+
+See `docs/stream_browser_modes.md` for how this fits the broadcast-coupled
+search routing.