test: isolate AF_UNIX socket paths + ambient HOME state (#4279 classes 2 & 4)

[abhay-codes07]

Related issue

Addresses #4279 (classes 2 & 4). Together with #4363 (classes 1 & 3) this covers all four classes.

Summary

The remaining two test-isolation gaps from #4279. Both are macOS / Databricks-dev-box-specific at runtime — I validated non-regression on a Windows checkout and followed the issue's prescribed fixes and the in-repo precedents, but the macOS-only failure modes (AF_UNIX 103-byte cap, real Keychain) aren't reproducible on my box, so I'm flagging them as pattern-applied rather than executed on the failing platform.

Class 2 — AF_UNIX 103-byte path cap

macOS caps a Unix socket path at ~103 bytes and its $TMPDIR is already ~48, so pytest's tmp_path (which embeds the test name) overflows before a socket filename is appended. The repo already solves this with a short_tmp_parent fixture (tests/inner/egress/test_relay.py), just not in the two other socket-binding tests. Promoted a shared short_tmp_parent to tests/inner/conftest.py and used it in:

• test_proxy.py::test_proxy_start_unix
• test_terminal.py::test_server_survives_inner_process_exit_real_tmux

Class 4 — host state outside OMNIGENT_CONFIG_HOME

Ambient provider detection also reads ~/.codex/config.toml and ~/.databrickscfg (under $HOME), and on macOS _claude_login_detected() falls back to claude auth status, which reads the Keychain — no $HOME override can hide it. Fixes:

• Redirect $HOME (and $USERPROFILE, so os.path.expanduser is isolated cross-platform) to a temp dir in test_openai_agents_sdk_spawn_env.py and test_provider_spawn_env.py.
• Stub ambient._claude_login_detected -> False for the Keychain case.
• Scope the same $HOME redirect into the one affected runner test (test_create_session_threads_workspace_to_pi_cwd).

Test Plan

Verified on a Windows checkout:

OMNIGENT_SKIP_WEB_UI=true uv run pytest \
  tests/runtime/test_provider_spawn_env.py \
  tests/runtime/test_openai_agents_sdk_spawn_env.py \
  "tests/runner/test_app_sessions_native_terminals_runtime.py::test_create_session_threads_workspace_to_pi_cwd"
# 99 passed  (Class-4 isolation is additive — no regression)

The Class-2 tests use AF_UNIX, which is unsupported on Windows, so they behave identically to clean main there (the short_tmp_parent fixture itself runs fine); their macOS path-length fix is validated by the established test_relay.py precedent. ruff check + ruff format --check clean.

Demo

N/A. Test-only change (socket-path + env isolation); no product code touched.

Type of change

• Bug fix
• Feature
• UI / frontend change
• Refactor / chore
• Docs
• Test / CI
• Breaking change

Test coverage

• Unit tests added / updated
• Integration tests added / updated
• E2E tests added / updated
• Manual verification completed
• Existing tests cover this change
• Not applicable

Note for a macOS reviewer

If you can run uv run python -m pytest tests/inner tests/runtime on a signed-in Mac with a gateway-pinned shell + ~/.codex/config.toml + multi-profile ~/.databrickscfg, these are the tests #4279 lists for classes 2 & 4 — a green run there confirms the runtime fix I couldn't exercise on Windows.

Changelog

Isolated the AF_UNIX socket paths and ambient $HOME/Keychain provider state in the affected tests so pytest is a usable local signal on macOS.

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