refactor(gateway): move the voice helpers into the transcription mixin

655aef56d89 moved the transcription methods into
GatewayInboundTranscriptionMixin but left _prepend_media_prefix (with its
_EMPTY_TEXT_PLACEHOLDER), _untranscribed_audio_note and
_transcribe_one_clip in run_inbound.py, though only the mixin calls them.
They move unchanged; asyncio is imported for _transcribe_one_clip.
No behaviour change: the voice/STT suites pass (14 files, 260 tests).

Review finding by @kshitijk4poor on #140973
Refs #134889 (MSG-22)
Refs #140719

gateway/run_inbound.py

@@ -1838,46 +1838,3 @@ class GatewayInboundMixin(GatewayInboundHooksMixin, GatewayInboundTranscriptionM
             return user_text
         prefix = "\n\n".join(enriched_parts)
         return f"{prefix}\n\n{user_text}" if user_text else prefix
-
-    _EMPTY_TEXT_PLACEHOLDER = "(The user sent a message with no text content)"
-
-    @classmethod
-    def _prepend_media_prefix(cls, prefix: str, user_text: str) -> str:
-        """``prefix`` + the user's text; the Discord empty-content placeholder is dropped as redundant."""
-        if user_text and user_text.strip() != cls._EMPTY_TEXT_PLACEHOLDER:
-            return f"{prefix}\n\n{user_text}"
-        return prefix
-
-    @staticmethod
-    def _untranscribed_audio_note(path: str) -> str:
-        """One minimal neutral marker for every STT failure. Never mention "no STT provider" or setup
-        steps — persisted in history they make the model keep volunteering STT-setup advice."""
-        from tools.credential_files import to_agent_visible_cache_path
-        agent_path = to_agent_visible_cache_path(os.path.abspath(path))
-        return f"[voice message could not be transcribed automatically; the audio is available at: {agent_path}]"
-
-    async def _transcribe_one_clip(self, path: str, transcribe_audio, transcribe_audio_local_fallback) -> tuple[Optional[str], str]:
-        """``(transcript_or_None, note)`` for one clip via configured STT with local fallback."""
-        result = await asyncio.to_thread(transcribe_audio, path, None, "gateway")
-        if not result.get("success"):
-            fallback = await asyncio.to_thread(transcribe_audio_local_fallback, path)
-            if fallback.get("success"):
-                logger.info("Configured STT failed for %s; recovered with local STT", path)
-                result = fallback
-        if not result["success"]:
-            logger.info("Voice transcription failed for %s: %s", path, result.get("error", "unknown error"))
-            return None, self._untranscribed_audio_note(path)
-        transcript = result["transcript"]
-        # STT may return success=True with an empty/whitespace transcript (silence, cut-off);
-        # empty quotes make the agent reply to nothing and can loop, so emit a sentinel note.
-        # See #41603.
-        if not (transcript or "").strip():
-            return None, (
-                "[The user sent a voice message but it came through "
-                "empty or inaudible — speech-to-text returned no "
-                "words. Do not guess at the content; ask the user "
-                "to resend or type it out.]"
-            )
-        # Plain quoted line: a "The user sent a voice message..." wrapper read as a meta-instruction
-        # and made the LLM comment on voice mode instead.
-        return transcript, f'"{transcript}"'

gateway/run_inbound_transcription.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import asyncio
 import logging
 import os
 from typing import Optional
@@ -141,3 +142,46 @@ class GatewayInboundTranscriptionMixin:
         except Exception as trans_exc:
             logger.warning("%s transcription failed: %s", log_context, trans_exc)
             return text, []
+
+    _EMPTY_TEXT_PLACEHOLDER = "(The user sent a message with no text content)"
+
+    @classmethod
+    def _prepend_media_prefix(cls, prefix: str, user_text: str) -> str:
+        """``prefix`` + the user's text; the Discord empty-content placeholder is dropped as redundant."""
+        if user_text and user_text.strip() != cls._EMPTY_TEXT_PLACEHOLDER:
+            return f"{prefix}\n\n{user_text}"
+        return prefix
+
+    @staticmethod
+    def _untranscribed_audio_note(path: str) -> str:
+        """One minimal neutral marker for every STT failure. Never mention "no STT provider" or setup
+        steps — persisted in history they make the model keep volunteering STT-setup advice."""
+        from tools.credential_files import to_agent_visible_cache_path
+        agent_path = to_agent_visible_cache_path(os.path.abspath(path))
+        return f"[voice message could not be transcribed automatically; the audio is available at: {agent_path}]"
+
+    async def _transcribe_one_clip(self, path: str, transcribe_audio, transcribe_audio_local_fallback) -> tuple[Optional[str], str]:
+        """``(transcript_or_None, note)`` for one clip via configured STT with local fallback."""
+        result = await asyncio.to_thread(transcribe_audio, path, None, "gateway")
+        if not result.get("success"):
+            fallback = await asyncio.to_thread(transcribe_audio_local_fallback, path)
+            if fallback.get("success"):
+                logger.info("Configured STT failed for %s; recovered with local STT", path)
+                result = fallback
+        if not result["success"]:
+            logger.info("Voice transcription failed for %s: %s", path, result.get("error", "unknown error"))
+            return None, self._untranscribed_audio_note(path)
+        transcript = result["transcript"]
+        # STT may return success=True with an empty/whitespace transcript (silence, cut-off);
+        # empty quotes make the agent reply to nothing and can loop, so emit a sentinel note.
+        # See #41603.
+        if not (transcript or "").strip():
+            return None, (
+                "[The user sent a voice message but it came through "
+                "empty or inaudible — speech-to-text returned no "
+                "words. Do not guess at the content; ask the user "
+                "to resend or type it out.]"
+            )
+        # Plain quoted line: a "The user sent a voice message..." wrapper read as a meta-instruction
+        # and made the LLM comment on voice mode instead.
+        return transcript, f'"{transcript}"'