[skygunner]

Problem

controller_tui test fixtures run scripts through /bin/sh. The child inherited the test process's global PATH, and other tests in this binary legitimately replace that process-global environment. When a concurrently running test had rewritten PATH, the fixture's external utility lookups failed non-deterministically (observed as sleep: command not found), producing failures unrelated to the behavior under test.

Change

The fixture now sets a child-local PATH (/usr/bin:/bin) on the spawned shell instead of inheriting the process environment. This is test-only: no production code, CLI behavior, or global environment is modified.

The regression runs the fixture in an isolated child process whose inherited PATH contains no shell utilities. The fixture's own script calls an external utility (sleep), so the child process can only succeed when the command lookup is child-local. The parent test asserts the isolated probe actually ran and passed, so a filter that matches nothing cannot report a false success.

Scope: POSIX only, matching the existing fixture (/bin/sh, #[cfg(unix)]). The fixture already requires a POSIX layout; pinning the two standard system directories does not assume Nix or Homebrew layouts.

Validation

cargo test --locked -p webcodex-cli --lib controller_fixture
  -> 1 passed; 1 ignored; 545 filtered out

With the child-local PATH removed (change reverted), the same tests fail:
  fixture utility lookup failed: /bin/sh: line 1: sleep: command not found
  test result: FAILED. 0 passed; 1 failed; 1 ignored; 545 filtered out

The ignored probe is invoked explicitly by its parent test; it is not meant to run in the ordinary parallel pool. Not run here: macOS and Windows lanes (no environment available; the fixture is POSIX-only by construction).

[yyjeqhc]

Reviewed the scoped implementation and regression coverage against its source baseline; CI and diff checks pass. No blocking issue identified.