fix: add download retry to cache_audio_from_url matching cache_image_from_url (#3401)

PR #3323 added retry with exponential backoff to cache_image_from_url
but missed the sibling function cache_audio_from_url 18 lines below in
the same file. A single transient 429/5xx/timeout loses voice messages
while image downloads now survive them.

Apply the same retry pattern: 3 attempts with 1.5s exponential backoff,
immediate raise on non-retryable 4xx.

gateway/platforms/base.py

@@ -175,29 +175,51 @@ def cache_audio_from_bytes(data: bytes, ext: str = ".ogg") -> str:
     return str(filepath)
 
 
-async def cache_audio_from_url(url: str, ext: str = ".ogg") -> str:
+async def cache_audio_from_url(url: str, ext: str = ".ogg", retries: int = 2) -> str:
     """
     Download an audio file from a URL and save it to the local cache.
 
+    Retries on transient failures (timeouts, 429, 5xx) with exponential
+    backoff so a single slow CDN response doesn't lose the media.
+
     Args:
         url: The HTTP/HTTPS URL to download from.
         ext: File extension including the dot (e.g. ".ogg", ".mp3").
+        retries: Number of retry attempts on transient failures.
 
     Returns:
         Absolute path to the cached audio file as a string.
     """
+    import asyncio
     import httpx
+    import logging as _logging
+    _log = _logging.getLogger(__name__)
 
+    last_exc = None
     async with httpx.AsyncClient(timeout=30.0, follow_redirects=True) as client:
-        response = await client.get(
+        for attempt in range(retries + 1):
-            url,
+            try:
-            headers={
+                response = await client.get(
-                "User-Agent": "Mozilla/5.0 (compatible; HermesAgent/1.0)",
+                    url,
-                "Accept": "audio/*,*/*;q=0.8",
+                    headers={
-            },
+                        "User-Agent": "Mozilla/5.0 (compatible; HermesAgent/1.0)",
-        )
+                        "Accept": "audio/*,*/*;q=0.8",
-        response.raise_for_status()
+                    },
-        return cache_audio_from_bytes(response.content, ext)
+                )
+                response.raise_for_status()
+                return cache_audio_from_bytes(response.content, ext)
+            except (httpx.TimeoutException, httpx.HTTPStatusError) as exc:
+                last_exc = exc
+                if isinstance(exc, httpx.HTTPStatusError) and exc.response.status_code < 429:
+                    raise
+                if attempt < retries:
+                    wait = 1.5 * (attempt + 1)
+                    _log.debug("Audio cache retry %d/%d for %s (%.1fs): %s",
+                               attempt + 1, retries, url[:80], wait, exc)
+                    await asyncio.sleep(wait)
+                    continue
+                raise
+    raise last_exc
 
 
 # ---------------------------------------------------------------------------

tests/gateway/test_media_download_retry.py

@@ -171,6 +171,170 @@ class TestCacheImageFromUrl:
         mock_sleep.assert_not_called()
 
 
+# ---------------------------------------------------------------------------
+# cache_audio_from_url (base.py)
+# ---------------------------------------------------------------------------
+
+class TestCacheAudioFromUrl:
+    """Tests for gateway.platforms.base.cache_audio_from_url"""
+
+    def test_success_on_first_attempt(self, tmp_path, monkeypatch):
+        """A clean 200 response caches the audio and returns a path."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        fake_response = MagicMock()
+        fake_response.content = b"\x00\x01 fake audio"
+        fake_response.raise_for_status = MagicMock()
+
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(return_value=fake_response)
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client):
+                from gateway.platforms.base import cache_audio_from_url
+                return await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg"
+                )
+
+        path = asyncio.run(run())
+        assert path.endswith(".ogg")
+        mock_client.get.assert_called_once()
+
+    def test_retries_on_timeout_then_succeeds(self, tmp_path, monkeypatch):
+        """A timeout on the first attempt is retried; second attempt succeeds."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        fake_response = MagicMock()
+        fake_response.content = b"audio data"
+        fake_response.raise_for_status = MagicMock()
+
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(
+            side_effect=[_make_timeout_error(), fake_response]
+        )
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        mock_sleep = AsyncMock()
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client), \
+                 patch("asyncio.sleep", mock_sleep):
+                from gateway.platforms.base import cache_audio_from_url
+                return await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg", retries=2
+                )
+
+        path = asyncio.run(run())
+        assert path.endswith(".ogg")
+        assert mock_client.get.call_count == 2
+        mock_sleep.assert_called_once()
+
+    def test_retries_on_429_then_succeeds(self, tmp_path, monkeypatch):
+        """A 429 response on the first attempt is retried; second attempt succeeds."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        ok_response = MagicMock()
+        ok_response.content = b"audio data"
+        ok_response.raise_for_status = MagicMock()
+
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(
+            side_effect=[_make_http_status_error(429), ok_response]
+        )
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client), \
+                 patch("asyncio.sleep", new_callable=AsyncMock):
+                from gateway.platforms.base import cache_audio_from_url
+                return await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg", retries=2
+                )
+
+        path = asyncio.run(run())
+        assert path.endswith(".ogg")
+        assert mock_client.get.call_count == 2
+
+    def test_retries_on_500_then_succeeds(self, tmp_path, monkeypatch):
+        """A 500 response on the first attempt is retried; second attempt succeeds."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        ok_response = MagicMock()
+        ok_response.content = b"audio data"
+        ok_response.raise_for_status = MagicMock()
+
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(
+            side_effect=[_make_http_status_error(500), ok_response]
+        )
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client), \
+                 patch("asyncio.sleep", new_callable=AsyncMock):
+                from gateway.platforms.base import cache_audio_from_url
+                return await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg", retries=2
+                )
+
+        path = asyncio.run(run())
+        assert path.endswith(".ogg")
+        assert mock_client.get.call_count == 2
+
+    def test_raises_after_max_retries_exhausted(self, tmp_path, monkeypatch):
+        """Timeout on every attempt raises after all retries are consumed."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(side_effect=_make_timeout_error())
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client), \
+                 patch("asyncio.sleep", new_callable=AsyncMock):
+                from gateway.platforms.base import cache_audio_from_url
+                await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg", retries=2
+                )
+
+        with pytest.raises(httpx.TimeoutException):
+            asyncio.run(run())
+
+        # 3 total calls: initial + 2 retries
+        assert mock_client.get.call_count == 3
+
+    def test_non_retryable_4xx_raises_immediately(self, tmp_path, monkeypatch):
+        """A 404 (non-retryable) is raised immediately without any retry."""
+        monkeypatch.setattr("gateway.platforms.base.AUDIO_CACHE_DIR", tmp_path / "audio")
+
+        mock_sleep = AsyncMock()
+        mock_client = AsyncMock()
+        mock_client.get = AsyncMock(side_effect=_make_http_status_error(404))
+        mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+        mock_client.__aexit__ = AsyncMock(return_value=False)
+
+        async def run():
+            with patch("httpx.AsyncClient", return_value=mock_client), \
+                 patch("asyncio.sleep", mock_sleep):
+                from gateway.platforms.base import cache_audio_from_url
+                await cache_audio_from_url(
+                    "http://example.com/voice.ogg", ext=".ogg", retries=2
+                )
+
+        with pytest.raises(httpx.HTTPStatusError):
+            asyncio.run(run())
+
+        # Only 1 attempt, no sleep
+        assert mock_client.get.call_count == 1
+        mock_sleep.assert_not_called()
+
+
 # ---------------------------------------------------------------------------
 # Slack mock setup (mirrors existing test_slack.py approach)
 # ---------------------------------------------------------------------------