refactor(discord): delegate ffmpeg discovery to shared tools.transcription_tools helper

Keep one owner for PATH/local-prefix ffmpeg discovery: ffmpeg_utils now
delegates to tools.transcription_tools._find_ffmpeg_binary and only adds
the Discord-specific FFMPEG_PATH override and Windows winget fallback on
top (follow-up to PR #60627 by @LauraGPT, fixes #60624).

plugins/platforms/discord/ffmpeg_utils.py

@@ -1,4 +1,11 @@
-"""Shared ffmpeg executable discovery for Discord voice paths."""
+"""Shared ffmpeg executable discovery for Discord voice paths.
+
+Discovery itself is owned by ``tools.transcription_tools`` (the same helper
+the STT pipeline uses — PATH plus common Homebrew/local prefixes); this module
+only layers the Discord-voice-specific extras on top: an explicit
+``FFMPEG_PATH`` override and a Windows winget fallback for installs that
+never touch PATH.
+"""
 
 from __future__ import annotations
 
@@ -7,13 +14,22 @@ import shutil
 from pathlib import Path
 
 
+def _shared_find_ffmpeg():
+    """Delegate to the repo-wide ffmpeg discovery helper when importable."""
+    try:
+        from tools.transcription_tools import _find_ffmpeg_binary
+    except ImportError:  # standalone plugin import (tests / sandboxes)
+        return shutil.which("ffmpeg")
+    return _find_ffmpeg_binary()
+
+
 def resolve_ffmpeg_executable() -> str:
     """Return an ffmpeg command that also covers common Windows installs."""
     explicit = os.getenv("FFMPEG_PATH")
     if explicit and explicit.strip():
         return os.path.expandvars(os.path.expanduser(explicit.strip()))
 
-    discovered = shutil.which("ffmpeg")
+    discovered = _shared_find_ffmpeg()
     if discovered:
         return discovered
 

tests/gateway/test_voice_command.py

@@ -757,10 +757,22 @@ class TestVoiceReceiver:
 
         monkeypatch.delenv("FFMPEG_PATH", raising=False)
         monkeypatch.setenv("LOCALAPPDATA", str(tmp_path))
-        monkeypatch.setattr(ffmpeg_utils.shutil, "which", lambda _cmd: None)
+        # Discovery delegates to tools.transcription_tools; simulate "not found".
+        monkeypatch.setattr(ffmpeg_utils, "_shared_find_ffmpeg", lambda: None)
 
         assert ffmpeg_utils.resolve_ffmpeg_executable() == str(ffmpeg)
 
+    def test_ffmpeg_resolver_delegates_to_shared_helper(self, monkeypatch):
+        """PATH/local-prefix discovery is owned by tools.transcription_tools."""
+        from plugins.platforms.discord import ffmpeg_utils
+
+        monkeypatch.delenv("FFMPEG_PATH", raising=False)
+        monkeypatch.setattr(
+            "tools.transcription_tools._find_ffmpeg_binary", lambda: "/opt/homebrew/bin/ffmpeg"
+        )
+
+        assert ffmpeg_utils.resolve_ffmpeg_executable() == "/opt/homebrew/bin/ffmpeg"
+
     def test_pcm_to_wav_uses_resolved_ffmpeg_executable(self, monkeypatch, tmp_path):
         """Receiver conversion should use the same resolved executable as playback."""
         from plugins.platforms.discord import adapter as discord_adapter