python-test-environment-isolation

Answer

Root cause. test_install.py's two bare-wrapper tests simulated bridge-absence by (a) copying the wrapper alone to a tmp dir (so search orders 2–3 — same-dir and ../plugin/ — miss), and (b) trusting that the ambient python3 cannot import the pip-installed terminal_jail package, so _find_bridge()'s python-module fallback (search order 4) also misses. That assumption breaks under uv run: uv puts the venv bin/ on PATH, python3 becomes the venv interpreter, search order 4 finds the bridge → the wrapper's interruptor engages → the "bridge not available" warning never appears (test 1 fails) and the firewall blocks the marker command, exiting 126 (test 2 fails).

Fix. TERMINAL_JAIL_BRIDGE is the wrapper's explicit override (search order 1). The wrapper treats an explicit override as authoritative: a missing file is a hard failure (wrapper L82) with no fall-through to order 4. Pin it to a guaranteed-missing path (a unique tmp_path subpath, so it can never exist on any host) in the two tests' env:

# test_install.py

def bridge_absent_env(tmp_path: Path) -> dict:
    """Explicit override = hard failure (wrapper L82, no fall-through to the
    python-module search). Pinning a guaranteed-missing path makes
    bridge-absence deterministic on every host — ambient python3, the repo
    venv, or a fresh `uv run` venv with terminal_jail pip-installed."""
    return {"TERMINAL_JAIL_BRIDGE": str(tmp_path / "no-bridge" / "interruptor_bridge.py")}


def test_bare_wrapper_warns_when_bridge_absent(bare_wrapper: Path, tmp_path: Path) -> None:
    result = _run(bare_wrapper, "echo hi", env=bridge_absent_env(tmp_path))
    assert result.returncode == 0
    assert "interruptor bridge not available" in result.stderr
    assert "hi" in result.stdout


def test_bare_wrapper_runs_without_firewall_when_bridge_absent(bare_wrapper: Path, tmp_path: Path) -> None:
    result = _run(bare_wrapper, "printf 'ran-%s' TERMINAL_JAIL_FORBIDDEN",
                  env=bridge_absent_env(tmp_path))
    assert result.returncode == 0
    assert result.stdout.strip() == "ran-TERMINAL_JAIL_FORBIDDEN"

Key points: the pin must be non-empty (an empty TERMINAL_JAIL_BRIDGE is treated as unset and falls through to order 4) and absolute/missing (a path under pytest's unique tmp_path is guaranteed absent, unlike /nonexistent/… which is only conventionally absent). The wrapper's _find_bridge() already provides the required hard-failure semantics:

# wrapper, search order 1 (L82 = the hard-failure return)
if [ -n "${TERMINAL_JAIL_BRIDGE:-}" ]; then
    if [ -f "$TERMINAL_JAIL_BRIDGE" ]; then echo "$TERMINAL_JAIL_BRIDGE"; return 0; fi
    return 1          # explicit override missing ⇒ hard failure, NO fall-through
fi
# ... orders 2 (same-dir), 3 (../plugin/), 4 (python module import)