diff --git a/tests/tools/test_tts_output_timestamp.py b/tests/tools/test_tts_output_timestamp.py
new file mode 100644
index 00000000000..235d7d262d2
--- /dev/null
+++ b/tests/tools/test_tts_output_timestamp.py
@@ -0,0 +1,36 @@
+"""Regression test for salvaged PR #43911 — microsecond TTS output timestamps.
+
+Default output paths used second-resolution ``%Y%m%d_%H%M%S`` timestamps, so
+two text_to_speech_tool calls landing in the same wall-clock second produced
+the same filename and the second synthesis overwrote the first. The format
+now appends ``%f`` (microseconds).
+"""
+
+import datetime
+import re
+
+
+class TestDefaultOutputTimestampResolution:
+    def test_default_output_path_uses_microsecond_timestamp(self):
+        """The source must build default filenames with a %f component."""
+        import inspect
+
+        from tools import tts_tool
+
+        src = inspect.getsource(tts_tool.text_to_speech_tool)
+        assert "%Y%m%d_%H%M%S_%f" in src, (
+            "default TTS output timestamp lost its microsecond component — "
+            "concurrent calls in the same second would collide again (#43911)"
+        )
+
+    def test_microsecond_format_distinguishes_same_second_instants(self):
+        fmt = "%Y%m%d_%H%M%S_%f"
+        base = datetime.datetime(2026, 7, 28, 12, 0, 0, 1)
+        later_same_second = base.replace(microsecond=2)
+        assert base.strftime(fmt) != later_same_second.strftime(fmt)
+        # And the rendered value still parses back to the same instant.
+        assert datetime.datetime.strptime(base.strftime(fmt), fmt) == base
+
+    def test_timestamp_component_is_filename_safe(self):
+        stamp = datetime.datetime.now().strftime("%Y%m%d_%H%M%S_%f")
+        assert re.fullmatch(r"\d{8}_\d{6}_\d{6}", stamp)