fix(main): defer hide() in hideOnClose handler past windowShouldClose:

[MaxLeiter]

Bug

On macOS, clicking the red traffic-light on a hideOnClose pool window quits the consumer's entire app, not just the popout. Cmd+W on the same window works correctly.

Reported and root-caused in anthropics/apps#43100 (closed unmerged in favor of fixing it here, per @alicelovescake).

Root cause

WindowInstance's close handler does event.preventDefault() then browserWindow.hide() synchronously. The two close paths diverge at the native layer:

• Red button → AppKit -[NSWindow performClose:] → -windowShouldClose: delegate → emits JS close. The handler's hide() → -[NSWindow orderOut:] runs while still inside windowShouldClose:, which trips app termination.
• Cmd+W → focused.close() → NativeWindowMac::Close() → emits JS close directly (no delegate). Same handler runs, no termination.

Fix

Wrap the hide() in setImmediate(...) so windowShouldClose: returns NO before the window orders out. The preventDefault() and UserCloseRequested event stay synchronous so consumers see no API change. The isDestroyed() guard re-evaluates inside the deferred callback to handle a force-close racing the deferred hide.

The defer is unconditional (not Darwin-gated) — one event-loop tick is harmless on Windows/Linux and keeps the code path uniform.

Observable change

The renderer receives UserCloseRequested while the window is still visible for ~1 tick (previously it was already hidden). The Hidden event still fires when the deferred orderOut: runs, so anything that genuinely depends on visibility should be listening for that instead.

Tests

Two new unit tests in tests/unit/main-process.test.ts:

• hideOnClose: defers hide() past the close event, preventDefault stays synchronous — asserts hide() is not called inside the close dispatch and is called on the next tick.
• hideOnClose: deferred hide() is a no-op if the window was destroyed in between — guards the race against a destroy() between the close event and the deferred hide.

yarn test:unit: 174 passed. yarn typecheck, yarn lint, yarn format:check: clean.

Verification

Verified working on macOS by @alicelovescake against an earlier iteration of the same defer in anthropics/apps#43100. The exact patch in that PR (against the built dist/) is byte-equivalent to this change in src/.

Related

• fix(main): disarm hideOnClose veto on app quit so the drain completes #19 also touches this close handler (_forceClosing, app-quit drain). The two changes are orthogonal — fix(main): disarm hideOnClose veto on app quit so the drain completes #19 disarms the veto so the close proceeds on quit; this PR fixes the case where the veto is intentional. Should rebase cleanly in either order.

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