fix(desktop): complete backend PATH for Homebrew Codex

[y0shua1ee]

Fixes #44813

Summary

/codex-runtime on in the macOS Desktop app can still fail when codex is installed via Homebrew at /opt/homebrew/bin/codex. The Desktop dashboard backend PATH may include Hermes-managed bins and the default Apple paths, while still missing Apple Silicon Homebrew.

This follows the two existing fixes in the same bug family:

• [Bug]: macOS gateway terminal PATH skips Homebrew dirs when /usr/bin exists #35613 / fix(terminal): complete sane PATH entries on POSIX (salvage of #35614) #42653: terminal/gateway subprocesses append missing POSIX sane PATH entries individually.
• [Bug]: /codex-runtime on fails on macOS desktop — dashboard inherits minimal PATH without ~/.hermes/node/bin #41385 / fix(desktop): extend PATH for dashboard backend so codex is discoverable on macOS #41389: Desktop backend should prepend Hermes-managed Node and venv bins so ~/.hermes/node/bin/codex is discoverable.

What changed

• Added apps/desktop/electron/backend-env.cjs:
  • prepends ~/.hermes/node/bin and the backend venv bin;
  • appends missing POSIX sane PATH entries (/opt/homebrew/bin, /opt/homebrew/sbin, /usr/local/sbin, etc.);
  • preserves caller PATH precedence and drops duplicates/empty entries;
  • preserves Windows PATH key casing and ; delimiters.
• Wired both Desktop backend descriptors through that helper:
  • createPythonBackend() for explicit/dev source checkouts;
  • createActiveBackend() for the installed active checkout.
• Added apps/desktop/electron/backend-env.test.cjs and included it in test:desktop:platforms.

Behavior change

A GUI-launched Desktop backend with a minimal macOS PATH can now discover both:

• Hermes-managed binaries such as ~/.hermes/node/bin/codex;
• Homebrew binaries such as /opt/homebrew/bin/codex.

That lets /codex-runtime on enable codex_app_server when Codex is installed through Homebrew.

Tests

zsh -lic 'node --check electron/backend-env.cjs && node --check electron/backend-env.test.cjs && node --check electron/main.cjs'
# passed

zsh -lic 'node --test electron/backend-env.test.cjs electron/backend-probes.test.cjs'
# tests 12, pass 12, fail 0

zsh -lic 'npm run test:desktop:platforms'
# tests 171, pass 170, fail 0, skipped 1

Risk / scope

This only affects the Electron Desktop backend subprocess environment. It does not change the model tool schema or terminal tool execution path. Windows behavior is covered by a regression test for PATH casing and delimiter preservation.

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