[Quaii]

PR description — here's a filled-out version based on what we verified:

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What this PR does

Implements the scroll-reactive bottom navigation on iOS and Android with a hybrid precompression + threshold-settle collapse (instead of the earlier immediate-collapse approach). Adds a user-configurable behavior setting — Reactive, Expanded, or Compact — in Settings. Also adds StrandMotion.navigationBarCollapse / navigationBarExpand animation tokens to the design system.

Type of change

• New feature

How it was tested

UI-only change; no BLE path touched. Tested visually on device — scroll-down triggers precompression then settles to compact, scroll-up expands immediately. Behavior setting updates the bar live from Settings. Reduce Motion snaps rather than interpolates.

Checklist

• Swift package tests pass for any package I touched (swift test in Packages/)
• Android unit tests pass if I touched android/ (./gradlew testFullDebugUnitTest)
• No new build warnings introduced
• UI changes use only StrandDesign tokens — no hardcoded colors, fonts, or spacing
• No hardcoded hex frame bytes; protocol facts live in the schema / decoders
• Follows the conventions in docs/CONTRIBUTING.md
• I did not commit generated output (Strand.xcodeproj/) or any secrets/keystores

Related issues

Part of #86

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[ryanbr]

Thanks for this — it's a careful implementation and the cross-platform parity is genuinely well done. One blocker and one thing to verify before it can land.

🔴 Blocker: the Android side doesn't compile

AppRoot.kt:335 references NestedScrollSource.UserInput, which doesn't exist in this project's Compose version. app/build.gradle.kts pins Compose BOM 2024.06.00, and NestedScrollSource.UserInput wasn't introduced until Compose 1.7 (BOM 2024.09+). This version only has .Drag / .Fling.

Fix — use the pre-1.7 equivalent for user-drag gestures:

// AppRoot.kt:335
if (delta > 0f && source == NestedScrollSource.Drag) {

I applied that locally and the whole module then compiled clean (compileFullDebugKotlin) and the unit suite passed — so it's the only Android compile error, a one-line change. This lines up with the checklist: ./gradlew testFullDebugUnitTest is unchecked, so the Android side hadn't been built yet. Worth running it before pushing the fix.

🟡 Please verify the Swift app-target compiles

The checklist covers swift test for the package you touched (StrandDesign / Motion tokens — that part is CI-covered and fine). But RootTabView.swift, ScreenScaffold.swift, SettingsView.swift, and LiquidTodayView.swift are app-target Swift, and no default CI compiles those (app-build.yml is disabled). A compile error there passes every green check.

I confirmed statically that the symbols resolve (NoopMotion.gated, NoopMetrics.space1/2/3/5/6/controlHeight, the new StrandMotion.navigationBar{Collapse,Expand}, and the #if os(iOS)-scoped env keys / PreferenceKey), and the #if os(iOS) gating looks right — but that's not a compile guarantee. Please build both app targets locally (xcodebuild … Strand for macOS and NOOPiOS for iOS, since ScreenScaffold/SettingsView/LiquidTodayView are shared and must compile for both), or I can kick off an app-build run on the branch.

🟢 What's already solid

• Parity is correct despite a real trap — the two platforms name spacing tokens differently (Swift spaceN is a scale index → space6 = 24pt; Android spaceN is the dp value → space24 = 24dp). The mapping came out right: collapse threshold 24 = 24, noise floor 0.5 = 0.5, precompression 0.16 on both. The behavior matches.
• Setting parity: same key noop.bottomBarBehavior, same reactive/expanded/compact values, same default, loaded on launch.
• Design tokens: this actually improves compliance — hardcoded 2/7/8/22 spacing became NoopMetrics.space*, and StrandAlpha.navigationGlass / Metrics.tabBarClearance are named tokens.
• Reduce Motion handled on both (snap vs interpolate, state preserved at the 0.5 threshold), and no BLE path is touched.

Minor: the new preference isn't in the .noopbak whitelist — fine for a device-local UI choice, just flagging it's intentionally not backed up.

Once the .Drag fix is in and both app targets build, this is good to go.

[Quaii]

Fixed: NestedScrollSource.UserInput → .Drag in AppRoot.kt:335 (commit 88e3a63).

All 3 Platforms compile fine :)

[tigercraft4]

Heads up: #90 (by the maintainer) is an open prototype for the same scroll-reactive bottom bar on #86 — Android-only, simpler immediate-collapse. This PR is broader (both platforms + configurable behavior + design tokens), so it may supersede #90, but flagging so they get reconciled rather than landing independently.