fix(tts): fall through to raw import when lazy_deps fails (#53259)

Replace 
aise ImportError(str(e)) with pass in the except Exception
handler of _import_edge_tts(), _import_elevenlabs(), and
_import_mistral_client() so packages installed via PYTHONPATH or Docker
layered filesystems still work when lazy_deps.ensure() raises.

Also fix the Mistral STT path in transcription_tools.py which only
caught ImportError, not FeatureUnavailable.

Adds 6 regression tests using sys.modules fixtures (no
builtins.__import__ patching).

tests/tools/test_tts_pythonpath_fallback.py

@@ -0,0 +1,103 @@
+"""Regression tests for #53259.
+
+When TTS packages (edge-tts, elevenlabs, mistralai) installed outside the
+venv but importable on sys.path (e.g. via PYTHONPATH, Docker layered
+filesystems), the lazy-import helpers must fall through to the raw import
+instead of re-raising lazy_deps.ensure() failures as ImportError.
+
+Uses sys.modules fixtures so builtins.__import__ stays intact — patching
+__import__ replaces the helper's own ``from tools.lazy_deps import ...``
+and defeats the purpose of the test.
+"""
+
+import sys
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from tools.lazy_deps import FeatureUnavailable
+
+
+@pytest.fixture(autouse=True)
+def _clean_tts_modules():
+    """Remove TTS packages from sys.modules so each test starts fresh."""
+    removed = {}
+    for name in ("edge_tts", "elevenlabs", "elevenlabs.client",
+                 "mistralai", "mistralai.client"):
+        if name in sys.modules:
+            removed[name] = sys.modules.pop(name)
+    yield
+    for name in ("edge_tts", "elevenlabs", "elevenlabs.client",
+                 "mistralai", "mistralai.client"):
+        sys.modules.pop(name, None)
+    sys.modules.update(removed)
+
+
+class TestEdgeTtsPythonpathFallback:
+    def test_falls_through_on_lazy_deps_failure(self):
+        """FeatureUnavailable from ensure() must not prevent raw import."""
+        mock_edge_tts = MagicMock()
+        with patch.dict(sys.modules, {"edge_tts": mock_edge_tts}), \
+             patch("tools.lazy_deps.ensure",
+                   side_effect=FeatureUnavailable("tts.edge", (), "test")):
+            from tools.tts_tool import _import_edge_tts
+            result = _import_edge_tts()
+        assert result is mock_edge_tts
+
+    def test_raises_when_package_truly_missing(self):
+        """When the package is truly absent, ImportError must propagate."""
+        with patch("tools.lazy_deps.ensure"), \
+             patch.dict(sys.modules, {"edge_tts": None}):
+            from tools.tts_tool import _import_edge_tts
+            with pytest.raises(ImportError):
+                _import_edge_tts()
+
+
+class TestElevenLabsPythonpathFallback:
+    def test_falls_through_on_lazy_deps_failure(self):
+        """FeatureUnavailable from ensure() must not prevent raw import."""
+        mock_cls = MagicMock()
+        mock_client_pkg = MagicMock()
+        mock_client_pkg.ElevenLabs = mock_cls
+        with patch.dict(sys.modules, {
+            "elevenlabs": mock_client_pkg,
+            "elevenlabs.client": mock_client_pkg,
+        }), patch("tools.lazy_deps.ensure",
+                  side_effect=FeatureUnavailable("tts.elevenlabs", (), "test")):
+            from tools.tts_tool import _import_elevenlabs
+            result = _import_elevenlabs()
+        assert result is mock_cls
+
+    def test_raises_when_package_truly_missing(self):
+        """When the package is truly absent, ImportError must propagate."""
+        with patch("tools.lazy_deps.ensure"), \
+             patch.dict(sys.modules, {"elevenlabs": None,
+                                      "elevenlabs.client": None}):
+            from tools.tts_tool import _import_elevenlabs
+            with pytest.raises(ImportError):
+                _import_elevenlabs()
+
+
+class TestMistralPythonpathFallback:
+    def test_falls_through_on_lazy_deps_failure(self):
+        """FeatureUnavailable from ensure() must not prevent raw import."""
+        mock_cls = MagicMock()
+        mock_mistralai = MagicMock()
+        mock_mistralai.Mistral = mock_cls
+        with patch.dict(sys.modules, {
+            "mistralai": mock_mistralai,
+            "mistralai.client": mock_mistralai,
+        }), patch("tools.lazy_deps.ensure",
+                  side_effect=FeatureUnavailable("tts.mistral", (), "test")):
+            from tools.tts_tool import _import_mistral_client
+            result = _import_mistral_client()
+        assert result is mock_cls
+
+    def test_raises_when_package_truly_missing(self):
+        """When the package is truly absent, ImportError must propagate."""
+        with patch("tools.lazy_deps.ensure"), \
+             patch.dict(sys.modules, {"mistralai": None,
+                                      "mistralai.client": None}):
+            from tools.tts_tool import _import_mistral_client
+            with pytest.raises(ImportError):
+                _import_mistral_client()