fix(tools): correct Python-fallback bugs in calculator, file tools, a…

[TacoengineerIT]

Summary

Fixed 9 real bugs across 4 source files discovered via static analysis and
manual code review. All bugs affect the Python fallback path (active when the
Rust extension is not compiled); two are cross-platform regressions that fail
on Windows.

Problem

1. calculator.py — 6 bugs in the Python AST fallback

Expression	Expected	Actual (before fix)
safe_eval("2^10")	1024.0	ValueError — Python ^ is XOR, not power
safe_eval("ln(e)")	1.0	ValueError: Unknown function: ln
safe_eval("1/0")	math.inf	ZeroDivisionError unhandled
safe_eval("2 +")	ValueError	SyntaxError — broke pytest.raises(ValueError)
safe_eval("x + 1")	raises "unknown variable"	Capital U broke regex match
CalculatorTool.execute("1/0")	success=True, content="inf"	success=False

2. file_read.py / file_write.py — cross-platform path check

_is_path_allowed used str(path).startswith(str(d) + "/") with a hardcoded
/ separator. On Windows (os.sep = \) this never matched, so
allowed_dirs always denied access — even to permitted paths.

3. git_tool.py — unhandled NotADirectoryError on Windows

_run_git did not catch NotADirectoryError (WinError 267), raised by
subprocess.run when cwd is a non-existent directory. The exception
propagated instead of returning ToolResult(success=False).

Solution

• calculator: pre-process ^→**, add ln alias, convert SyntaxError→ValueError, return math.inf on
  division by zero, fix error message casing
• file_read / file_write: replace startswith(str(d) + "/") with Path.is_relative_to(d) (OS-agnostic, Python ≥
  3.9)
• git_tool: add except NotADirectoryError handler in _run_git

Testing

• Existing tests pass (uv run pytest tests/ -v)
• tests/tools/test_calculator.py — 25/25 (was 6 failed)
• tests/tools/test_file_read.py — test_allowed_dirs_permits passes
• tests/tools/test_file_write.py — test_allowed_dirs_permits passes
• tests/tools/test_git_tool.py — test_invalid_repo_path passes

Notes

Found via static analysis + manual code review of the full codebase. Bugs live
in the Python fallback path — invisible when openjarvis_rust is compiled, but
they surface immediately for contributors who skip maturin develop.