perf(pos-app): speed up amount entry on low-end devices

[ignaciosantise]

Summary

Makes the amount screen respond faster on low-end Android POS hardware. The existing BigAmountInput animation and visuals are unchanged.

• Stable keypad handler: app/amount.tsx now uses plain useState with a stable onKeyPress. Before, a new inline handler on every render stopped the memoized NumericKeyboard from skipping renders, so all 12 keys re-rendered on each press. This removes react-hook-form, which only this screen used; the lockfile change is just its own entries.
• Cached separators: formatAmount.ts looks up the decimal and group separators once per locale. Before, each key press built three Intl.NumberFormat instances, which is slow on Android Hermes because it goes through Java ICU.
• Reanimated sync UI props: ANDROID_SYNCHRONOUSLY_UPDATE_UI_PROPS and IOS_SYNCHRONOUSLY_UPDATE_UI_PROPS are turned on in package.json. A Perfetto profile showed about 37% of the UI thread going to Reanimated committing the full shadow tree on every animation frame. With the flags, transform and opacity updates skip that commit.
• AnimatedCharacter: plain Text instead of Animated.Text.

Measurements

Release builds on a low-end Android POS terminal (MediaTek MT6761, 4× Cortex-A53, 1.8 GB RAM). A scripted adb typing sequence (1234567.89 then 10 backspaces) ran ×5 per run, 3 baseline runs vs 2 final runs.

Per key press (p50)	Before	After
JS work, normal typing (250ms between taps)	77ms	37ms
Key press → next frame, normal typing	103ms	60ms
JS work, rapid typing (~80ms between taps)	87ms	39ms
Key press → next frame, rapid typing	185ms	94ms

The janky-frame % under rapid typing did not change (~14%).

Testing

• Android release build on the POS terminal: the amount renders the same as main, and every scripted tap registered
• iOS simulator (dev JS on an existing binary): the amount renders correctly. An earlier version of this change used a zero-width translateX anchor, which broke iOS; it was reverted.
• npm test (309 passing), lint, type check
• iOS build with a fresh pod install, to confirm IOS_SYNCHRONOUSLY_UPDATE_UI_PROPS
• Web

Native config changed (Reanimated static flags), so native builds need a clean prebuild or pod install.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
pos-demo	Ready	Preview	Sep 30, 2026 5:45pm UTC

2 Skipped Deployments

Project	Deployment	Actions	Updated
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react-native-walletkit	Ignored		Sep 30, 2026 5:45pm UTC

[claude]

Claude finished @ignaciosantise's task in 2m 36s —— View job

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Code Review

• Read changed files
• License compliance check
• Breaking changes check
• Post review findings

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License compliance: ✅ No issues — react-hook-form (MIT) removed, no new deps introduced.

Breaking changes: ✅ No breaking changes — all exported symbols and component contracts are unchanged; pos-app is a private app.

Found 2 issue(s)

Issue 1: Unnecessary handlePress closure layer prevents full key memoization

ID: numeric-keyboard-handlepress-closure-a3f1
File: dapps/pos-app/components/numeric-keyboard.tsx:27-29
Severity: LOW
Category: performance

Context:

• Pattern: handlePress is a local closure that just forwards to onKeyPress, then each Pressable wraps it in another arrow () => handlePress(key) — two closure layers with no benefit.
• Risk: Every render of NumericKeyboardBase allocates 12 new closures (one per key). In normal usage the memoized NumericKeyboard doesn't re-render during typing, so this is benign — but if anything causes a keyboard re-render, the Pressable children all get new onPress references.
• Impact: No functional bug, but the double-indirection obscures the intent and partially undercuts the memo optimization this PR adds.
• Trigger: Any re-render of NumericKeyboardBase (theme change, orientation change).

Recommendation:

// Remove handlePress entirely; inline onKeyPress directly
onPress={() => onKeyPress(key)}

Fix this →

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Issue 2: IOS_SYNCHRONOUSLY_UPDATE_UI_PROPS is a native-config change with unchecked iOS test

ID: package-ios-sync-ui-props-untested-b8c2
File: dapps/pos-app/package.json:29-34
Severity: MEDIUM
Category: test_coverage

Context:

• Pattern: staticFeatureFlags.IOS_SYNCHRONOUSLY_UPDATE_UI_PROPS: true is compiled into the Reanimated Babel plugin output — it affects every useAnimatedStyle / withTiming / withSpring call in the entire app on iOS, not just the amount screen.
• Risk: The PR's own checklist marks "iOS build with a fresh pod install" as unchecked. If the flag triggers an assertion in the Reanimated native module (e.g., accessing the shadow tree on the wrong thread), it silently breaks all animations app-wide on iOS.
• Impact: Potential animation regressions across the whole iOS app (amount screen, scan screen, any other screens using Reanimated).
• Trigger: First iOS release build after pod install with the new flag.

Recommendation: Confirm the iOS native build passes with IOS_SYNCHRONOUSLY_UPDATE_UI_PROPS: true before merging (the PR's own checkbox covers this). If the flag is not yet validated on iOS, consider shipping only ANDROID_SYNCHRONOUSLY_UPDATE_UI_PROPS: true initially and following up with the iOS flag after the pod install test passes.