fix(android): space the New thread FAB 16dp from the edge and tab bar

[PixPMusic]

Problem

On the compact Android thread list, the New thread FAB sat about 17dp from the right edge and 32dp above the tab bar. The right margin used right-5, a rem value, so it grew with the app's text size. The bottom offset put a 16dp floor under the safe-area inset and then added another 16dp, even though the tab bar already absorbs the navigation bar inset.

Change

The FAB and the filter button stacked above it now take their position from one helper, androidHomeFabPosition in AndroidHomeFab.shared.tsx: a fixed 16dp right margin (Material's FAB margin, in dp so it does not scale with text size) and safe-area-bottom + 16dp in the compact list. The expanded sidebar keeps its old bottom offset. The filter button is still stacked 8dp above the FAB.

Taken over from @PixPMusic's original #18578, which found the right values. The rebuild folds the helper into the existing shared FAB module instead of a new file and exposes one position object so the two controls cannot drift apart.

Verification

Original author's measurements on an Android 17 Pixel Fold emulator (cover display, 2.44 px/dp). These historical captures show the intended spacing; they are not visual verification of the rebuilt head.

Before	After

• Right gap 42px to 39px, gap above the tab bar 78px to 39px. Both are now 16dp.
• Added tests: 0 → 0; the existing FAB scroll suite passes all 4 tests.
• Mobile typecheck, lint and format on the three touched files pass.
• Two independent reviews of the rebuilt diff found no blocking issues. Code tracing confirms the compact tab bar consumes the bottom inset, while layouts without that bar pass the actual inset. Nonzero insets and 3-button navigation still need native runtime verification.

Readiness blocker — missing current-head native proof: the native device tool returned “Agent device access is turned off for this environment”, so the rebuilt head was not rendered. Nonzero bottom insets and 3-button navigation need Android verification. iOS does not render this FAB. macOS, Windows, and Electron desktop were not exercised.

Rebuilt by Claude Fable 5.1 in Claude Code, running in T3 Code.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Approved at 4f83c53

Macroscope's review found this PR approvable — This is a narrowly scoped Android layout correction that centralizes FAB positioning and changes only fixed spacing around existing controls. It introduces no new capability, data or infrastructure behavior, schema changes, or static-analysis overrides.

^{You can add or adjust custom eligibility rules. Learn more.}

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📥 Commits

Reviewing files that changed from the base of the PR and between 81e3570 and 3858803.

📒 Files selected for processing: 3

• apps/mobile/src/features/home/AndroidHomeFab.android.tsx
• apps/mobile/src/features/home/AndroidHomeFab.shared.tsx
• apps/mobile/src/features/home/ThreadListToolbar.tsx

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📥 Commits

Reviewing files that changed from the base of the PR and between 9067e59 and 81e3570.

📒 Files selected for processing: 2

• apps/mobile/src/features/home/AndroidHomeFab.android.tsx
• apps/mobile/src/features/home/ThreadListToolbar.tsx

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📝 Walkthrough

The Android home FAB and thread list filter FAB now use a shared right-margin constant and bottom-positioning helper. The helper calculates the bottom offset from the safe-area inset and sidebar state.

Changes: Android FAB positioning

Layer / File(s)	Summary
Shared positioning helper apps/mobile/src/features/home/android-home-fab-position.ts	Adds a 16 dp right-margin constant and a helper that calculates the bottom offset from the safe-area inset and sidebar state.
FAB and filter menu positioning apps/mobile/src/features/home/AndroidHomeFab.android.tsx, apps/mobile/src/features/home/ThreadListToolbar.tsx	Both FAB containers use the shared right margin and bottom-positioning helper. The filter FAB retains its additional fabSize + 8 offset.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 81e35

The shared offsets preserve the compact safe-area spacing and the filter button’s 8 dp gap from the New thread button. No actionable positioning issue is established, so the change is ready to merge subject to normal checks.

Pre-merge checks: 3 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check		The description explains the problem, change, and verification, but it omits the required Scope and approval section. It also names an implementation file and position object that do not match the rep…	Add the Scope and approval section with the triaged issue or explicit maintainer approval, or explain why this focused fix qualifies for an exemption. Correct the implementation details to match android-home-fab-position.ts, ANDROID_HOME_FA…

Passed checks: 3 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title is concise, conventional, and accurately identifies the Android FAB spacing fix.

Full details: Description check

Explanation

The description explains the problem, change, and verification, but it omits the required Scope and approval section. It also names an implementation file and position object that do not match the reported diff, and its screenshots are historical rather than from the current head.

Resolution

Add the Scope and approval section with the triaged issue or explicit maintainer approval, or explain why this focused fix qualifies for an exemption. Correct the implementation details to match android-home-fab-position.ts, ANDROID_HOME_FAB_MARGIN, and androidHomeFabBottom. Provide current-head Android screenshots and document any remaining unverified navigation configurations.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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[juliusmarminge]

Taking over this one. Will bring in main, trim it to the minimum, and push to this branch.

Dismissing prior approval to re-evaluate 4f83c53