diff --git a/src/takopi/bridge.py b/src/takopi/bridge.py
index c27bdb6..d61c3ae 100644
--- a/src/takopi/bridge.py
+++ b/src/takopi/bridge.py
@@ -409,7 +409,7 @@ async def handle_message(
         if resume_token_value is None:
             resume_token_value = progress_renderer.resume_token
         progress_renderer.resume_token = resume_token_value
-        err_body = f"Error:\n{error}"
+        err_body = str(error)
         final_md = progress_renderer.render_final(elapsed, err_body, status="error")
         logger.debug("[error] markdown: %s", final_md)
         final_msg, edited = await _send_or_edit_markdown(
@@ -463,9 +463,9 @@ async def handle_message(
     final_answer = answer
     if run_ok is False and run_error:
         if final_answer.strip():
-            final_answer = f"{final_answer}\n\nError:\n{run_error}"
+            final_answer = f"{final_answer}\n\n{run_error}"
         else:
-            final_answer = f"Error:\n{run_error}"
+            final_answer = str(run_error)
 
     status = (
         "error" if run_ok is False else ("done" if final_answer.strip() else "error")
diff --git a/src/takopi/runners/codex.py b/src/takopi/runners/codex.py
index 6e354bd..073aafd 100644
--- a/src/takopi/runners/codex.py
+++ b/src/takopi/runners/codex.py
@@ -39,6 +39,25 @@ _ACTION_KIND_MAP: dict[str, ActionKind] = {
 }
 
 _RESUME_RE = re.compile(r"(?im)^\s*`?codex\s+resume\s+(?P<token>[^`\s]+)`?\s*$")
+_ANSI_ESCAPE_RE = re.compile(r"\x1b\[[0-9;]*[A-Za-z]")
+_TRUSTED_DIR_RE = re.compile(r"not inside a trusted directory", re.IGNORECASE)
+
+
+def _strip_ansi(text: str) -> str:
+    return _ANSI_ESCAPE_RE.sub("", text)
+
+
+def _extract_stderr_reason(stderr_tail: str) -> str | None:
+    if not stderr_tail:
+        return None
+    cleaned = _strip_ansi(stderr_tail)
+    lines = [line.strip() for line in cleaned.splitlines() if line.strip()]
+    if not lines:
+        return None
+    for line in lines:
+        if _TRUSTED_DIR_RE.search(line):
+            return line
+    return lines[-1]
 
 
 def _started_event(token: ResumeToken, *, title: str) -> StartedEvent:
@@ -558,7 +577,11 @@ class CodexRunner(ResumeTokenMixin, JsonlSubprocessRunner):
         stderr_tail: str,
         state: CodexRunState,
     ) -> list[TakopiEvent]:
-        message = f"codex exec failed (rc={rc})."
+        reason = _extract_stderr_reason(stderr_tail)
+        if reason:
+            message = f"codex exec failed (rc={rc}).\n\n{reason}"
+        else:
+            message = f"codex exec failed (rc={rc})."
         resume_for_completed = found_session or resume
         return [
             self.note_event(
diff --git a/tests/test_exec_runner.py b/tests/test_exec_runner.py
index 5d7cd9c..e673876 100644
--- a/tests/test_exec_runner.py
+++ b/tests/test_exec_runner.py
@@ -243,6 +243,30 @@ async def test_codex_runner_preserves_warning_order(tmp_path) -> None:
     assert seen[2].answer == "ok"
 
 
+@pytest.mark.anyio
+async def test_codex_runner_includes_stderr_reason(tmp_path) -> None:
+    codex_path = tmp_path / "codex"
+    codex_path.write_text(
+        "#!/usr/bin/env python3\n"
+        "import sys\n"
+        "\n"
+        "sys.stderr.write('Not inside a trusted directory and --skip-git-repo-check was not specified.\\n')\n"
+        "sys.stderr.flush()\n"
+        "sys.exit(1)\n",
+        encoding="utf-8",
+    )
+    codex_path.chmod(0o755)
+
+    runner = CodexRunner(codex_cmd=str(codex_path), extra_args=[])
+    events = [evt async for evt in runner.run("hi", None)]
+
+    completed = next(evt for evt in events if isinstance(evt, CompletedEvent))
+    assert completed.ok is False
+    assert completed.error is not None
+    assert "codex exec failed (rc=1)." in completed.error
+    assert "\n\nNot inside a trusted directory" in completed.error
+
+
 @pytest.mark.anyio
 async def test_run_serializes_two_new_sessions_same_thread(
     tmp_path, monkeypatch