fix(ios): show a sidebar toggle on the unfolded iPhone Duo in portrait

[PixPMusic]

Problem

On the iPhone Duo unfolded in portrait, an open thread fills the screen and the thread list is hidden. The only way back to the list is an edge swipe, and nothing in the header hints at it. iPad shows a sidebar toggle in the same situation. Julius agreed in Discord that there should be a sidebar button there, top left.

Cause

Unfolded in portrait, the inner display (669×951pt, regular width) reports a hinge but no side bar and no fold division. The Duo rule in deriveLayout keys off those two signals, so this posture fell through to the iPad floor of 720pt and went compact. UIKit still kept the split expanded, so it showed the thread alone. With a compact layout the thread header never got the split view's sidebar toggle.

Fix

• deriveLayout also treats a display with a hinge as Duo geometry. Unfolded portrait now takes the same split path as iPad: the list sits beside the thread, and the thread header gets the sidebar toggle (Maximize content / Show thread sidebar).
• In that split, the Threads and Pull requests tab buttons sit at the leading edge of the thread list's bottom toolbar, with compose at the trailing edge, so they hide when the list collapses. Without this, UIKit's phone tab bar spread across both panes, its pill centered near the divider and its compose button under the thread, duplicating the header's. UIKit can't leading-align its floating tab bar, so it stays hidden in this posture. The Duo's side rail still carries UIKit's tabs when it has one, and iPad keeps its segmented picker, which now shares the tab selection logic.

Unfolded landscape already took the Duo path through its side rail, and the folded front screen reports a compact size class, so neither changes.

Verification

• Device metrics from the iOS 27.1 Duo simulator, read from useNativeLayoutMetrics:

  Posture	Size	Size class	Side bar	Layout before → after
  Unfolded, portrait	669×951	regular	none	compact → split
  Unfolded, landscape	951×669	regular	right	split → split
  Folded, portrait	466×678	compact	right	compact → compact
  Folded, landscape	678×466	compact	right	compact → compact

• vp test run apps/mobile/src/lib/reserved-regions.test.ts apps/mobile/src/lib/layout.test.ts: 49 passed. New cases use the measured unfolded-portrait metrics (split with the hinge, compact without it) and the folded metrics in both orientations.

• vp run typecheck in apps/mobile passes. vp lint and vp fmt --check on the changed files are clean.

• On the Duo, unfolded in portrait, with a synthetic showcase environment: the toggle hides and shows the list. The toolbar tabs switch between Threads and Pull requests, including from an open thread (which closes it), and the selected tab is highlighted. Collapsing the list hides the tabs, leaving compose only in the thread header. In unfolded landscape, the side rail and the list beside the thread look the same as on main.

• On an iPad simulator, the sidebar's segmented picker still switches tabs after the shared selection hook refactor.

• Not checked: the folded front screen visually. The simulator stream goes black while folded, so the folded rows above come from the metrics log only.

Before / After

iPhone Duo, unfolded, portrait.

	Before	After
Thread
Thread with list	—
Home

Model: Claude Opus 5.5 | Harness: Claude Code in T3 Code

[macroscopeapp]

Approvability

Verdict: Approved at 50ae77d

Macroscope's review found this PR approvable — This is a focused iOS Duo portrait layout fix with localized workspace toolbar changes and regression coverage for the affected device metrics. Existing iPad, folded Duo, Android, and side-rail paths remain accounted for, with no schema, infrastructure, security, or static-analysis changes.

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[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between c8bbdcc and 50ae77d.

📒 Files selected for processing: 5

• apps/mobile/src/features/workspace/WorkspaceRootScreen.tsx
• apps/mobile/src/features/workspace/WorkspaceSidebarTabs.ios.tsx
• apps/mobile/src/features/workspace/WorkspaceToolbar.ios.tsx
• apps/mobile/src/features/workspace/useSystemWorkspaceTabBar.ts
• apps/mobile/src/lib/layout.ts

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📝 Walkthrough

Duo layout detection now considers hinge metadata. iOS sidebar tabs can use picker or toolbar placement based on layout metrics. Tab selection is shared between the sidebar picker and toolbar controls.

Changes: Duo display layout

Layer / File(s)	Summary
Hinge geometry and layout tests apps/mobile/src/lib/layout.ts, apps/mobile/src/lib/reserved-regions.test.ts	deriveLayout now treats reported hinge metadata as Duo geometry. Tests cover unfolded displays with and without hinge metadata, and folded front-screen layouts.

iOS workspace tabs

Layer / File(s)	Summary
Sidebar-tab placement and picker layout apps/mobile/src/features/workspace/useSystemWorkspaceTabBar.ts, apps/mobile/src/features/workspace/WorkspaceRootScreen.tsx	The sidebar-tab hook returns "picker", "toolbar", or null based on platform and layout metrics. The workspace root applies picker layout behavior only in picker mode.
Tab selection and toolbar controls apps/mobile/src/features/workspace/useSelectWorkspaceTab.ts, apps/mobile/src/features/workspace/WorkspaceSidebarTabs.ios.tsx, apps/mobile/src/features/workspace/WorkspaceToolbar.ios.tsx	A shared hook handles tab selection, keyboard dismissal, and navigation-stack popping. The sidebar picker uses the hook. When tabs are assigned to the toolbar, it displays Threads and Pull requests buttons with selection-specific tint.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  actor User
  participant WorkspaceToolbar
  participant useSelectWorkspaceTab
  participant Keyboard
  participant Navigation
  participant WorkspaceState
  User->>WorkspaceToolbar: Select Threads or Pull requests
  WorkspaceToolbar->>useSelectWorkspaceTab: Select requested tab
  useSelectWorkspaceTab->>Keyboard: Dismiss keyboard
  useSelectWorkspaceTab->>Navigation: Pop to top when navigation index is truthy
  useSelectWorkspaceTab->>WorkspaceState: Dispatch tab selection

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Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 50ae7

The unfolded portrait Duo routes workspace tabs to the thread-list toolbar. No merge-blocking issue was identified; merge after normal checks.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main iOS Duo portrait-layout fix.
Description check		The description explains the problem, cause, fix, affected layouts, verification results, screenshots, and known limitation. It does not include a dedicated Scope and approval section or a link to the…
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.

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Dismissing prior approval to re-evaluate c8bbdcc

Dismissing prior approval to re-evaluate 50ae77d