## Why
Automatic startup work and `codex doctor` can run before a workspace is
trusted. A repository-controlled `PATH` must not be able to make those flows
execute workspace-provided helpers.
## What changed
- Resolve helpers used by automatic startup from trusted system installation
directories, and give plugin-sync Git subprocesses a sanitized environment.
- Make terminal detection environment-only and have doctor inspect executable
locations without running them. Fetch update metadata with the HTTP client
instead of `curl`.
- Fall back conservatively when trusted terminal helpers are unavailable,
including for tmux keyboard enhancement flags.
## Testing
Add black-box coverage with hostile workspace `PATH` entries for startup,
interactive tmux startup, support log collection, doctor, and curated plugin
sync. Add unit coverage for trusted executable resolution and bounded update
HTTP responses.
GitOrigin-RevId: 3b8995eb422b60ed53b0386951de59e8f9bfc542