fix(dev): forward termination signals to Electron child (#899)

[iddogino]

Summary

Fixes #899. In startElectron, forward SIGINT/SIGTERM/SIGHUP from the electron-vite parent to the spawned Electron child, matching Electron's own CLI wrapper (node_modules/electron/cli.js).

Why

electron-vite spawns the Electron binary directly via spawn(electronPath, ...) and does not trap signals. When the user hits Ctrl-C in a dev session:

• SIGINT is delivered to the foreground process group once.
• The Node parent has no SIGINT handler, so it exits immediately with Node's default behavior.
• The Electron child receives only that single SIGINT.

Under a direct ./node_modules/.bin/electron . launch the picture is different: the Electron CLI shim installs a handler that forwards SIGINT to its child, so the Electron child receives SIGINT twice (once from the pgroup, once forwarded). On macOS, an Electron app whose before-quit handler calls event.preventDefault() and then later calls app.quit() from an async continuation can stall in AppKit's event loop — never reaching [NSApp terminate:]. The second SIGINT forwarded by the shim is what knocks Electron out of that stuck state.

By matching that forwarding behavior in electron-vite, electron-vite dev now exits as cleanly as electron . does for that app.

A reduced test was run against the repro in the issue (https://github.com/iddogino/electron-vite-quit-repro):

scenario	result
unpatched, Ctrl-C via pty	hangs — 3 Electron processes lingering
parent kept alive but no forwarding	still hangs
parent kept alive and signal forwarded (this PR)	clean exit, 0 lingering

Notes on the implementation

• currentElectronPs tracks the latest-spawned child so that when the watch-on-rebuild path (server.ts) kills the old Electron and spawns a new one, signals go to the current child, not a stale reference.
• signalHandlersInstalled guards against accumulating process.on handlers across dev restarts.
• The ps.on('close', process.exit) behavior is unchanged, so a normal in-app quit still exits the parent as before.

Test plan

• pnpm run lint, pnpm run typecheck, pnpm run build all pass.
• prettier --check src/electron.ts passes.
• Built dist dropped into the repro — pty Ctrl-C exits cleanly (0 lingering Electron processes).
• Manual sanity test on the repro in a real terminal with Ctrl-C.
• Manual sanity test of the watch-restart path (edit src/main/index.js, confirm restart still works).

[alex8088]

Thanks for the PR. I will perform some local tests to verify the changes.

[callummr]

Have you had a chance to review this @alex8088 ? I have a use-case that will benefit from it as my main launches a few subprocesses and doesn't know to kill them without this patch. Cheers!