test: make path-handling tests pass on Windows runners

[Teerapat-Vatpitak]

Summary

• Fixes three pre-existing tests that pass on Linux CI but fail on Windows because of test-side platform assumptions, not application bugs.
• Touches only agent/tests/ — no production code changes.
• After this PR: full pytest sweep on Windows goes from 3 failed, 863 passed to 866 passed, 0 failed.

Why

A Windows contributor running pytest --ignore=agent/tests/e2e_backtest --tb=short -q against main hits these three failures:

FAILED agent/tests/test_backtest_runner_security.py::test_signal_engine_rejects_top_level_execution
FAILED agent/tests/test_backtest_runner_security.py::test_signal_engine_rejects_class_level_execution
FAILED agent/tests/test_loop_helpers.py::TestNormalizeToolRunDir::test_preserves_absolute_run_dir

Linux CI is unaffected, so the failures didn't surface in #80 / #82 / etc. The behaviour the tests exercise is correct on both platforms; only the test inputs make POSIX-specific assumptions.

What was actually wrong

1. test_backtest_runner_security.py — RCE path interpolation

Both failing tests build a signal_engine.py whose source contains pytest's tmp_path formatted into an os.system('touch ...') call. On Windows tmp_path resolves to e.g. C:\Users\teera\AppData\Local\Temp\pytest-25\.... Interpolated into a single-quoted Python string literal, the leading \U is interpreted as a (truncated) unicode escape:

ValueError: Invalid signal_engine.py syntax:
(unicode error) 'unicodeescape' codec can't decode bytes in position 8-9:
truncated \UXXXXXXXX escape

ast.parse raises SyntaxError before the security scrubber under test ever runs — so the test fails for the wrong reason on Windows, while passing on Linux because the path uses forward slashes there.

Fix: switch the interpolation to Path.as_posix(). Forward-slash paths survive Python source escaping intact while still pointing at the same filesystem location on every OS, so the scrubber gets a chance to see the actual class- / top-level statement and reject it as the test originally intended.

2. test_loop_helpers.py::TestNormalizeToolRunDir::test_preserves_absolute_run_dir

The test passed the literal "/var/tmp/custom_run" and expected it back unchanged from _normalize_tool_run_dir:

args = {"run_dir": "/var/tmp/custom_run"}
out = _normalize_tool_run_dir(args, "/tmp/run_123")
assert out["run_dir"] == "/var/tmp/custom_run"

_normalize_tool_run_dir calls Path.is_absolute(), which on Windows returns False for a bare drive-less path. The function then correctly treats the input as relative and joins it with memory_run_dir, yielding C:\var\tmp\custom_run. The function is doing the right thing — the test asserted POSIX semantics on a cross-platform helper.

Fix: resolve the test input through os.path.abspath before handing it to the function, so the input is the platform's actual absolute form (/var/tmp/custom_run on POSIX, C:\var\tmp\custom_run on Windows). The assertion then holds on both.

Verification

Before (on Windows / Python 3.12):

3 failed, 863 passed, 1 skipped, 2 warnings in 13.54s

After (same machine):

866 passed, 1 skipped, 2 warnings in 12.33s

The three previously-failing tests now pass without changing any production code. Linux CI continues to pass (the patches are no-ops on POSIX where forward slashes are already the path separator and /var/tmp/custom_run is already an absolute path).

Test plan

• Targeted run — the three previously-failing tests pass: pytest agent/tests/test_backtest_runner_security.py::test_signal_engine_rejects_top_level_execution agent/tests/test_backtest_runner_security.py::test_signal_engine_rejects_class_level_execution agent/tests/test_loop_helpers.py::TestNormalizeToolRunDir::test_preserves_absolute_run_dir -v → 3 passed.
• Full sweep on Windows — pytest --ignore=agent/tests/e2e_backtest --tb=line -q → 866 passed, 0 failed.
• Linux behaviour preserved — Path.as_posix() on POSIX is a no-op, and os.path.abspath('/var/tmp/custom_run') returns /var/tmp/custom_run unchanged.

Checklist

• No changes to protected areas (agent/src/agent/, agent/src/session/, agent/src/providers/) — only agent/tests/.
• No production code touched.
• No hardcoded secrets / paths.
• Code follows CONTRIBUTING.md (Conventional Commit prefix test:, Google-style docstrings via comments).
• Documentation updated — N/A.

[warren618]

Thanks for the focused Windows compatibility fix. I verified the targeted path-handling tests locally in a combined merge gate, and CI was already green, so this is now merged.