Test isolation: integration conftest leaks KALSHI_DEMO into unit from_env tests (4 full-suite failures)

[TexasCoding]

Summary

Four unit tests fail in the full pytest tests/ run but pass in isolation:

tests/test_client.py::TestKalshiClientFromEnv::test_from_env_demo_flag
tests/test_client.py::TestKalshiClientFromEnv::test_from_env_base_url_override
tests/test_async_client.py::TestAsyncKalshiClientFromEnv::test_from_env_demo_flag
tests/test_async_client.py::TestAsyncKalshiClientFromEnv::test_from_env_base_url_override

This is pre-existing (reproduces on main, independent of #443/PR #444) and is an environment-variable test-isolation leak.

Root cause

tests/integration/conftest.py has a session-scoped autouse fixture that does:

if "KALSHI_DEMO" not in os.environ:
    _monkeypatch_session.setenv("KALSHI_DEMO", "true")

_monkeypatch_session is a session-scoped MonkeyPatch, so it only undoes at session end — not between tests. Once the first test under tests/integration/ triggers fixture setup (the integration tests pytest.skip() in their bodies, but autouse fixtures still set up first), KALSHI_DEMO=true is set for the remainder of the session and leaks into later unit tests.

test_from_env_base_url_override sets KALSHI_API_BASE_URL but does not delenv("KALSHI_DEMO"), so from_env sees the leaked KALSHI_DEMO=true alongside an explicit base_url and raises the "Conflicting environment: demo=True together with explicit base_url" error.

Reproduction (deterministic)

uv run pytest tests/integration tests/test_client.py::TestKalshiClientFromEnv \
  tests/test_async_client.py::TestAsyncKalshiClientFromEnv -q -p no:randomly
# -> 4 failed, 8 passed, 313 skipped

Excluding tests/integration makes all four pass.

Suggested fixes (any one)

1. Make the demo-env autouse fixture function-scoped (or use a fresh MonkeyPatch per test), so KALSHI_DEMO doesn't persist across the session.
2. Have the TestKalshiClientFromEnv / TestAsyncKalshiClientFromEnv from_env tests monkeypatch.delenv("KALSHI_DEMO", raising=False) (they already delenv KALSHI_API_BASE_URL).
3. Add a session-end teardown that explicitly restores KALSHI_DEMO.

Option 1 fixes the class of bug (any unit test reading KALSHI_DEMO is currently exposed), so it's preferable.

[TexasCoding]

Correction + fix incoming (PR #444).

The leaked variable is KALSHI_PRIVATE_KEY_PATH, not KALSHI_DEMO as I first wrote. The actual failure is:

kalshi.errors.KalshiAuthError: Both KALSHI_PRIVATE_KEY and KALSHI_PRIVATE_KEY_PATH are set.

Mechanism: tests/integration/conftest.py::_bridge_env_vars (session-scoped autouse) bridges a developer's ambient KALSHI_DEMO_PRIVATE_KEY_PATH → KALSHI_PRIVATE_KEY_PATH for the whole session. test_from_env_demo_flag / test_from_env_base_url_override set KALSHI_PRIVATE_KEY but — unlike their passing siblings (test_from_env_with_pem_string, test_from_env_with_key_path) — never delenv("KALSHI_PRIVATE_KEY_PATH"), so from_env() sees both and raises. (This is why it only surfaces on machines with demo creds exported, including the maintainer's; CI without demo creds wouldn't bridge a path and wouldn't trip it.)

Fix: make the two non-hermetic tests match their siblings by dropping the ambient PEM path — monkeypatch.delenv("KALSHI_PRIVATE_KEY_PATH", raising=False) in both test_client.py and test_async_client.py. The session-scoped bridge itself is left as-is (session scope is required for the session-scoped integration clients); the right boundary to harden is the unit test's own env, consistent with the rest of the class. Will be closed by PR #444.