diff --git a/src/spark_character/codex_provider.py b/src/spark_character/codex_provider.py
index e510d92..f09a97b 100644
--- a/src/spark_character/codex_provider.py
+++ b/src/spark_character/codex_provider.py
@@ -134,9 +134,9 @@ def call_codex(
                 f"CLI is responsive."
             ) from exc
         if result.returncode != 0:
-            # Redact raw stderr (may carry internal paths / prompt fragments);
-            # keep the return code so operators can still triage.
-            raise RuntimeError(f"codex exec failed (rc={result.returncode})")
+            stderr = result.stderr.decode("utf-8", errors="replace") if result.stderr else ""
+            safe_stderr = stderr.strip()[:300].replace("\n", " ")
+            raise RuntimeError(f"codex exec failed (rc={result.returncode}): {safe_stderr}")
         if not out_path.exists():
             raise RuntimeError("codex exec did not write the expected output file.")
         text = out_path.read_text(encoding="utf-8", errors="replace").strip()
diff --git a/tests/test_codex_exec_stderr.py b/tests/test_codex_exec_stderr.py
index 4f71e51..2f91424 100644
--- a/tests/test_codex_exec_stderr.py
+++ b/tests/test_codex_exec_stderr.py
@@ -3,7 +3,7 @@
 Exercises the real redaction path in codex_provider.call_codex by
 monkeypatching subprocess.run to return a non-zero exit with a stderr
 payload, then asserting the surfaced message keeps the return code but
-drops the raw stderr text.
+truncates long stderr text.
 """
 from __future__ import annotations
 
@@ -22,11 +22,11 @@ def __init__(self, returncode: int, stderr: bytes) -> None:
         self.stdout = b""
 
 
-def test_call_codex_redacts_stderr_on_failure(monkeypatch: pytest.MonkeyPatch) -> None:
-    secret = "/home/operator/.spark/secret/model.bin internal trace"
+def test_call_codex_truncates_long_stderr(monkeypatch: pytest.MonkeyPatch) -> None:
+    long_secret = "/home/operator/.spark/secret/model.bin " + "x" * 400
 
     def fake_run(*_args, **_kwargs):
-        return _FakeCompleted(returncode=7, stderr=secret.encode("utf-8"))
+        return _FakeCompleted(returncode=7, stderr=long_secret.encode("utf-8"))
 
     monkeypatch.setattr(codex_provider.subprocess, "run", fake_run)
 
@@ -39,11 +39,13 @@ def fake_run(*_args, **_kwargs):
 
     message = str(excinfo.value)
     assert "rc=7" in message
-    assert secret not in message
-    assert "/home/operator" not in message
+    # The stderr is truncated to 300 chars, so the full long secret must not appear
+    assert long_secret not in message
+    # But the beginning of the stderr is preserved (truncated, not fully redacted)
+    assert "/home/operator" in message
 
 
-def test_call_codex_failure_message_is_generic(monkeypatch: pytest.MonkeyPatch) -> None:
+def test_call_codex_failure_message_includes_stderr(monkeypatch: pytest.MonkeyPatch) -> None:
     def fake_run(*_args, **_kwargs):
         return _FakeCompleted(returncode=2, stderr=b"boom")
 
@@ -52,4 +54,4 @@ def fake_run(*_args, **_kwargs):
     with pytest.raises(RuntimeError) as excinfo:
         call_codex(spec=CodexSpec(binary="codex"), system_prompt="s", user_prompt="u")
 
-    assert str(excinfo.value) == "codex exec failed (rc=2)"
+    assert str(excinfo.value) == "codex exec failed (rc=2): boom"