## Why
Core tests should branch on the executor's operating system, not on
runner details such as Docker or Wine. This keeps platform behavior
stable as new test backends are added and reserves Wine-specific skips
for actual runner debt.
## What
- Add `TestTargetOs` and target/host-aware skip helpers while keeping
`TestEnvironment` internal.
- Replace topology enum access with remote predicates and a narrow
Docker accessor.
- Migrate OS-semantic Wine skips, preserve runner-specific gaps, and
document the skip taxonomy.
## Validation
- `just test -p core_test_support`
- `just test -p codex-core
remote_test_env_can_connect_and_use_filesystem`
- `bazel test //codex-rs/core:core-all-wine-exec-test
--test_output=errors` reached test execution; unrelated existing
view-image, path, and timing failures remain.
- `just test -p codex-core` and `just test` reached broad test
execution; this checkout has unrelated helper, sandbox, and timing
failures.
Adam Perry @ OpenAI
9a79536e6b