The simulator loop — verification checklist & device matrix

A screen is finished when it survives this checklist on a real simulator, not when the code compiles. Budget as many loop iterations as it takes; the goal is "cannot find a flaw", not "looks fine".

Loop mechanics

1. Launch on the iOS Simulator (primary) — npx expo start + i, or your dev build. Android emulator second.
2. Screenshot the screen (simctl: xcrun simctl io booted screenshot s.png, or your agent's screenshot tool). Open the screenshot and study it — do not trust memory of what you wrote.
3. Interact: tap every control, type overlong text, background/foreground the app, rotate if supported.
4. For motion: screen-record the ENTIRE flow (xcrun simctl io booted recordVideo m.mov) — not just the hero transition. Watch it at full speed for feel, then scrub frame by frame. Stills cannot catch a one-frame flash, a dropped spring, or a keyboard jump-cut; only the recording can.
5. Fix → relaunch → re-verify. Never batch more than a few fixes between looks; regressions hide in batches.

If a UI-testing tool (e.g. Maestro) is available, script the flow's happy path once it stabilizes — taps, assertions, screenshots — so later changes re-verify for free.

Per-screen checklist

Layout

• Nothing clipped by the Dynamic Island / status bar; scrolled content passes under it with the intended fade/blur, not a hard edge
• Bottom CTA clears the home indicator (safe-area inset respected)
• Optical alignment: icons vs text baselines, centered things actually look centered (check at 2× zoom)
• Spacing rhythm consistent (no rogue 13px gaps in an 8pt system)
• Long text: 2× length titles truncate/wrap by design, not by accident
• Empty state, loading state, error state each verified by forcing them

Theming & type

• Dark mode AND light mode screenshots taken and inspected
• Dynamic Type at XL: no overlap, no clipped labels
• Contrast: secondary text still readable in both themes

Motion (evaluated on the full-flow recording, never on stills)

• Entrance plays once, correctly, on first mount (and NOT again on back-navigation)
• Gesture follows the finger 1:1; release springs with velocity; cancelling mid-gesture settles cleanly
• Frame-by-frame: no pop at animation start/end, no double-render flash, no one-frame white/wrong-theme/wrong-color frames during transitions
• Every modal/sheet cycle recorded: present, drag, dismiss, cancel — smooth in both directions
• Keyboard appear AND dismiss recorded: layout glides with it, focused input stays visible, nothing jump-cuts or reflows after settling
• Sustained 60 fps through every transition of the flow (measure with the perf monitor / Instruments, don't eyeball)
• Reduce Motion enabled → spatial animations become fades

Interaction

• Every tappable ≥ 44pt; press states visible; haptics where native controls would have them
• Keyboard: appears with the right type, doesn't cover the focused input, dismisses sensibly
• Back gesture (iOS edge swipe) works everywhere it should
• Rapid double-taps don't double-navigate or double-submit

State

• Background the app mid-flow → return: state intact
• Kill and relaunch: persisted state restores, ephemeral state resets
• Offline: actions queue or fail loudly — never silently

Device matrix (minimum)

Run the full checklist on the primary; on the others, verify layout, safe areas, and the hero flow.