diff --git a/gateway/run.py b/gateway/run.py
index a3485ccb59..f28a40eb61 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -29412,6 +29412,13 @@ def _shutdown_gateway_health_export(runner: Any) -> None:
         logger.debug("gateway health OTLP export shutdown failed", exc_info=True)
 
 
+def _gateway_stderr_formatter() -> logging.Formatter:
+    """Return the redacting formatter used by the gateway stderr stream."""
+    from agent.redact import RedactingFormatter
+
+    return RedactingFormatter("%(asctime)s %(levelname)s %(name)s: %(message)s")
+
+
 async def start_gateway(config: Optional[GatewayConfig] = None, replace: bool = False, verbosity: Optional[int] = 0) -> bool:
     """
     Start the gateway and run until interrupted.
@@ -29641,12 +29648,10 @@ async def start_gateway(config: Optional[GatewayConfig] = None, replace: bool =
     # verbosity=1    (-v):         INFO and above
     # verbosity=2+   (-vv/-vvv):   DEBUG
     if verbosity is not None:
-        from agent.redact import RedactingFormatter
-
         _stderr_level = {0: logging.WARNING, 1: logging.INFO}.get(verbosity, logging.DEBUG)
         _stderr_handler = logging.StreamHandler(_safe_stderr())
         _stderr_handler.setLevel(_stderr_level)
-        _stderr_handler.setFormatter(RedactingFormatter('%(levelname)s %(name)s: %(message)s'))
+        _stderr_handler.setFormatter(_gateway_stderr_formatter())
         logging.getLogger().addHandler(_stderr_handler)
         # Lower root logger level if needed so DEBUG records can reach the handler
         if _stderr_level < logging.getLogger().level:
diff --git a/hermes_cli/stderr_timestamp.py b/hermes_cli/stderr_timestamp.py
index e16c152a39..83e8a20ac5 100644
--- a/hermes_cli/stderr_timestamp.py
+++ b/hermes_cli/stderr_timestamp.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import argparse
+import re
 import signal
 import subprocess
 import sys
@@ -11,13 +12,20 @@ from pathlib import Path
 from typing import BinaryIO, Sequence, TextIO
 
 
+_TIMESTAMP_PREFIX = re.compile(
+    r"^\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3}(?:\s|$)"
+)
+
+
 def _timestamp() -> str:
     """Match logging.Formatter's default ``%(asctime)s`` timestamp shape."""
     return datetime.now().strftime("%Y-%m-%d %H:%M:%S,%f")[:23]
 
 
 def _write_timestamped_line(log_file: TextIO, line: str) -> None:
-    log_file.write(f"{_timestamp()} {line.rstrip(chr(10))}\n")
+    rendered = line.rstrip("\r\n")
+    prefix = "" if _TIMESTAMP_PREFIX.match(rendered) else f"{_timestamp()} "
+    log_file.write(f"{prefix}{rendered}\n")
     log_file.flush()
 
 
diff --git a/tests/gateway/test_stderr_formatting.py b/tests/gateway/test_stderr_formatting.py
new file mode 100644
index 0000000000..1d6b27f53d
--- /dev/null
+++ b/tests/gateway/test_stderr_formatting.py
@@ -0,0 +1,28 @@
+"""Regression tests for operator-visible gateway stderr formatting."""
+
+from __future__ import annotations
+
+import logging
+import re
+
+from gateway.run import _gateway_stderr_formatter
+
+
+def test_gateway_stderr_formatter_includes_timestamp() -> None:
+    record = logging.LogRecord(
+        name="gateway.run",
+        level=logging.ERROR,
+        pathname=__file__,
+        lineno=1,
+        msg="delivery failed",
+        args=(),
+        exc_info=None,
+    )
+
+    rendered = _gateway_stderr_formatter().format(record)
+
+    assert re.fullmatch(
+        r"\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3} "
+        r"ERROR gateway\.run: delivery failed",
+        rendered,
+    )
diff --git a/tests/hermes_cli/test_stderr_timestamp.py b/tests/hermes_cli/test_stderr_timestamp.py
index 10b4c59dc3..6bda125b8f 100644
--- a/tests/hermes_cli/test_stderr_timestamp.py
+++ b/tests/hermes_cli/test_stderr_timestamp.py
@@ -11,7 +11,8 @@ def test_main_timestamps_each_stderr_line(tmp_path):
     code = (
         "import sys\n"
         "sys.stderr.write('first failure\\n')\n"
-        "sys.stderr.write('second failure without newline')\n"
+        "sys.stderr.write('second failure without newline\\n')\n"
+        "sys.stderr.write('2026-07-15 12:34:56,789 already timestamped')\n"
         "sys.exit(7)\n"
     )
 
@@ -29,6 +30,7 @@ def test_main_timestamps_each_stderr_line(tmp_path):
     assert rc == 7
     lines = log_path.read_text(encoding="utf-8").splitlines()
     timestamp = r"\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3}"
-    assert len(lines) == 2
+    assert len(lines) == 3
     assert re.fullmatch(f"{timestamp} first failure", lines[0])
     assert re.fullmatch(f"{timestamp} second failure without newline", lines[1])
+    assert lines[2] == "2026-07-15 12:34:56,789 already timestamped"