diff --git a/tests/tools/test_tts_command_providers.py b/tests/tools/test_tts_command_providers.py
index 616a88d7b88d..5bfe64125e78 100644
--- a/tests/tools/test_tts_command_providers.py
+++ b/tests/tools/test_tts_command_providers.py
@@ -14,6 +14,8 @@ differences) Windows.
 
 import json
 import os
+import shlex
+import subprocess
 import sys
 from pathlib import Path
 from unittest.mock import patch
@@ -37,6 +39,7 @@ from tools.tts_tool import (
     _render_command_tts_template,
     _resolve_command_provider_config,
     _resolve_max_text_length,
+    _run_command_tts,
     _shell_quote_context,
     check_tts_requirements,
     text_to_speech_tool,
@@ -57,6 +60,13 @@ def _python_copy_command(output_placeholder: str = "{output_path}") -> str:
     )
 
 
+def _shell_command(*args: str) -> str:
+    """Return a shell command string for subprocess.Popen(shell=True)."""
+    if os.name == "nt":
+        return subprocess.list2cmdline(list(args))
+    return " ".join(shlex.quote(str(arg)) for arg in args)
+
+
 # ---------------------------------------------------------------------------
 # _resolve_command_provider_config / built-in precedence
 # ---------------------------------------------------------------------------
@@ -348,6 +358,53 @@ class TestRenderCommandTtsTemplate:
         assert '"bob\'s voice"' in rendered
 
 
+# ---------------------------------------------------------------------------
+# _run_command_tts idle/progress timeout behavior
+# ---------------------------------------------------------------------------
+
+class TestRunCommandTts:
+    def test_stderr_progress_extends_beyond_timeout(self, tmp_path):
+        script = tmp_path / "progress_then_exit.py"
+        script.write_text(
+            "\n".join([
+                "import sys, time",
+                "for idx in range(4):",
+                "    print(f'tick {idx}', file=sys.stderr, flush=True)",
+                "    time.sleep(0.15)",
+                "print('done', flush=True)",
+            ]),
+            encoding="utf-8",
+        )
+
+        result = _run_command_tts(
+            _shell_command(sys.executable, "-u", str(script)),
+            timeout=0.25,
+        )
+
+        assert result.returncode == 0
+        assert "tick 3" in result.stderr
+        assert "done" in result.stdout
+
+    def test_silent_after_progress_still_times_out_with_stderr(self, tmp_path):
+        script = tmp_path / "progress_then_hang.py"
+        script.write_text(
+            "\n".join([
+                "import sys, time",
+                "print('starting tier 1', file=sys.stderr, flush=True)",
+                "time.sleep(1.0)",
+            ]),
+            encoding="utf-8",
+        )
+
+        with pytest.raises(subprocess.TimeoutExpired) as excinfo:
+            _run_command_tts(
+                _shell_command(sys.executable, "-u", str(script)),
+                timeout=0.2,
+            )
+
+        assert "starting tier 1" in (excinfo.value.stderr or "")
+
+
 # ---------------------------------------------------------------------------
 # End-to-end: _generate_command_tts
 # ---------------------------------------------------------------------------
diff --git a/tools/tts_tool.py b/tools/tts_tool.py
index 82dc5ad4f4d8..9a0c37d1393b 100644
--- a/tools/tts_tool.py
+++ b/tools/tts_tool.py
@@ -48,6 +48,7 @@ import shutil
 import subprocess
 import tempfile
 import threading
+import time
 import uuid
 from dataclasses import dataclass, field
 from pathlib import Path
@@ -999,7 +1000,7 @@ def _terminate_command_tts_process_tree(proc: subprocess.Popen) -> None:
 
 
 def _run_command_tts(command: str, timeout: float) -> subprocess.CompletedProcess:
-    """Run a command-provider shell command with process-tree timeout cleanup."""
+    """Run a command-provider shell command with process-tree idle cleanup."""
     from agent.delegation_context import delegated_child_subprocess_env
 
     popen_kwargs: Dict[str, Any] = {
@@ -1019,21 +1020,75 @@ def _run_command_tts(command: str, timeout: float) -> subprocess.CompletedProces
         popen_kwargs["start_new_session"] = True
 
     proc = subprocess.Popen(command, **popen_kwargs, stdin=subprocess.DEVNULL)
-    try:
-        stdout, stderr = proc.communicate(timeout=timeout)
-    except subprocess.TimeoutExpired as exc:
-        _terminate_command_tts_process_tree(proc)
+    output_queue: "queue.Queue[tuple[str, Optional[str]]]" = queue.Queue()
+    chunks: Dict[str, list[str]] = {"stdout": [], "stderr": []}
+    open_streams = {"stdout", "stderr"}
+
+    def read_stream(name: str, stream: Any) -> None:
         try:
-            stdout, stderr = proc.communicate(timeout=1)
-        except Exception:
-            stdout = getattr(exc, "output", None)
-            stderr = getattr(exc, "stderr", None)
+            while True:
+                chunk = stream.read(1)
+                if not chunk:
+                    break
+                output_queue.put((name, chunk))
+        finally:
+            output_queue.put((name, None))
+
+    readers = [
+        threading.Thread(
+            target=read_stream,
+            args=("stdout", proc.stdout),
+            daemon=True,
+        ),
+        threading.Thread(
+            target=read_stream,
+            args=("stderr", proc.stderr),
+            daemon=True,
+        ),
+    ]
+    for reader in readers:
+        reader.start()
+
+    deadline = time.monotonic() + timeout
+    timed_out = False
+    while open_streams:
+        remaining = deadline - time.monotonic()
+        if remaining <= 0:
+            timed_out = True
+            break
+        try:
+            name, chunk = output_queue.get(timeout=min(0.05, remaining))
+        except queue.Empty:
+            continue
+        if chunk is None:
+            open_streams.discard(name)
+            continue
+        chunks[name].append(chunk)
+        deadline = time.monotonic() + timeout
+
+    if timed_out:
+        _terminate_command_tts_process_tree(proc)
+        for reader in readers:
+            reader.join(timeout=0.5)
+        while True:
+            try:
+                name, chunk = output_queue.get_nowait()
+            except queue.Empty:
+                break
+            if chunk:
+                chunks[name].append(chunk)
+        stdout = "".join(chunks["stdout"])
+        stderr = "".join(chunks["stderr"])
         raise subprocess.TimeoutExpired(
             command,
             timeout,
             output=stdout,
             stderr=stderr,
-        ) from exc
+        )
+
+    stdout = "".join(chunks["stdout"])
+    stderr = "".join(chunks["stderr"])
+    proc.wait()
 
     if proc.returncode:
         raise subprocess.CalledProcessError(