Native macOS .app launcher + bundle

[MuJiongan]

What

A real macOS .app bundle so you can launch gorchestra from Spotlight/Dock/Launchpad instead of running make backend and make frontend in two terminals.

make app-install     # one-time: pywebview into the backend venv
make install-app     # build frontend + .app + drop into /Applications

Then Cmd+Space → gorchestra → Enter.

How

• launcher.py — runs FastAPI in a daemon thread on pinned port 8765, mounts frontend/dist/ as an SPA fallback, opens a native WKWebView via pywebview. private_mode=False so localStorage (API keys, default models) persists across launches. Port pin is required because localStorage is origin-scoped — a shifting port would orphan settings every relaunch.
• scripts/build_app.sh — produces gorchestra.app. The executable in Contents/MacOS/ is a tiny C wrapper compiled to native arm64 Mach-O that execvs the project's venv Python on launcher.py. A shell-script wrapper here would make LaunchServices misread the architecture and falsely demand Rosetta with a misleading -10669 error. Bundle is then ad-hoc signed so macOS 15+ App Management lets it launch.
• Graceful teardown — runner child is spawned with start_new_session=True; events.cancel uses killpg() so cancellation reaps the runner's grandchildren (shell-tool subprocesses) too. The pywebview closing event reuses the same teardown, so closing the window kills any in-flight runs cleanly.
• Force-quit teardown (parent-death watchdog) — the runner child holds the read end of a pipe whose write end the parent keeps open for the duration of the run. If the parent dies abruptly (SIGKILL, force-quit from Activity Monitor, segfault — anything that bypasses signal handlers and atexit), the kernel closes the write end, the child gets EOF instantly, and a daemon thread killpgs the child's own process group + _exits. Verified: SIGKILL on a parent with an active sleep grandchild reaps both within 2 seconds.

Targets

Target	What it does
make app-install	One-time: install pywebview into the backend venv
make app	Dev mode: launch in a window without bundling
make app-bundle	Build gorchestra.app in the project root
make install-app	Above + copy into /Applications

Caveats

• Bundle is hard-linked to this checkout — moves of the project directory require a make install-app rebuild. For a fully relocatable bundle, swap the C wrapper for py2app.
• make dev runs the frontend in your browser and uses that browser's localStorage. The native-window launches (make app and gorchestra.app) both run via Homebrew's embedded Python.app and share a single WKWebView store under ~/Library/WebKit/org.python.python/, so settings carry between those two — but not from the browser.

Verification

• make dev still works (backend on 8000, vite on 5173, vite proxy unchanged).
• 51/51 backend pytest tests pass on both commits.
• Empirical localStorage persistence test: write key in launch 1, read it back in launch 2 with same origin — value preserved.
• make install-app end-to-end: builds, installs to /Applications, launches via open, FastAPI binds 8765, WKWebView loads UI.
• Parent-death watchdog test: spawned a parent that ran a workflow whose node Popen'd sleep 60; SIGKILL on parent → both runner child and sleep grandchild gone within 2s.