fix(prompts): handle undecodable overrides

nanobot/utils/workspace_prompts.py

@@ -25,7 +25,7 @@ def load_workspace_prompt_override(
     Returns the loaded text and its original length. Missing, unreadable, and
     empty files return ``(None, 0)`` so callers can fall back to their default.
     """
-    with suppress(OSError):
+    with suppress(OSError, UnicodeDecodeError):
         text = path.read_text(encoding="utf-8").rstrip()
         if text:
             original_chars = len(text)
@@ -50,7 +50,7 @@ def initialize_workspace_prompt(path: Path, default_prompt: str) -> bool:
             not path.is_file() or bool(path.read_text(encoding="utf-8").strip())
         ):
             return False
-    except OSError:
+    except (OSError, UnicodeDecodeError):
         return False
 
     path.parent.mkdir(parents=True, exist_ok=True)

tests/agent/test_evaluator.py

@@ -56,6 +56,14 @@ def test_resolve_evaluator_prompt_uses_default_for_empty_override(tmp_path) -> N
     assert resolve_evaluator_prompt(tmp_path) == default_evaluator_prompt()
 
 
+def test_resolve_evaluator_prompt_uses_default_for_undecodable_override(tmp_path) -> None:
+    path = evaluator_prompt_file(tmp_path)
+    path.parent.mkdir()
+    path.write_bytes("Custom evaluator prompt.".encode("utf-16"))
+
+    assert resolve_evaluator_prompt(tmp_path) == default_evaluator_prompt()
+
+
 def test_resolve_evaluator_prompt_caps_workspace_override(tmp_path) -> None:
     path = evaluator_prompt_file(tmp_path)
     path.parent.mkdir()

tests/command/test_builtin_evaluator_prompt.py

@@ -59,6 +59,23 @@ async def test_evaluator_prompt_init_does_not_overwrite_existing_prompt(tmp_path
     assert prompt_file.read_text(encoding="utf-8") == "custom"
 
 
+@pytest.mark.asyncio
+async def test_evaluator_prompt_handles_undecodable_existing_prompt(tmp_path) -> None:
+    prompt_file = tmp_path / "prompts" / "evaluator.md"
+    prompt_file.parent.mkdir()
+    original = "custom".encode("utf-16")
+    prompt_file.write_bytes(original)
+
+    status = await cmd_evaluator_prompt(_make_ctx(tmp_path))
+    init = await cmd_evaluator_prompt(
+        _make_ctx(tmp_path, "/evaluator-prompt init", "init")
+    )
+
+    assert "Heartbeat evaluator prompt: nanobot default" in status.content
+    assert "already exists" in init.content
+    assert prompt_file.read_bytes() == original
+
+
 @pytest.mark.asyncio
 async def test_evaluator_prompt_init_recreates_empty_prompt(tmp_path) -> None:
     prompt_file = tmp_path / "prompts" / "evaluator.md"