fix(mobile): iOS 18 iPad sidebar and thread feed start below the header#32936

Problem

On iPadOS / iOS before 26 (no Liquid Glass, so the bars are solid), two lists start underneath their column's header. The native column lays content out under the bar, but these lists add no top inset there:

• In the iPad sidebar, the newest threads sit behind the title bar and the Search field.
• In the right-hand inspector pane showing a subagent, the top of the loaded page is behind the pane's header. The "Load earlier activity" button can't be tapped, and the first rows are hidden under the title.

The same happens to the top of an ordinary thread feed, to the empty-thread placeholder, and to the first message sent into an empty thread, on iPad and iPhone.

Change

• Sidebar: ThreadNavigationSidebar now uses UIKit's automatic content inset (contentInsetAdjustmentBehavior="automatic", with indicator insets) on every iOS version. Before, it was only on when glass was supported. UIKit then clears the bar and its stacked Search field. On iOS 26 the props are the same as before. The WORKSPACE_LIST_SCROLL_INSETS constant only existed to turn this off on iOS < 26, so it is removed.
• Feed: ThreadFeed no longer takes a contentTopInset prop. Its only caller always passed 0.
  • When the feed does not get the native contentInset (iOS < 26), its top inset is useContentTopInset(), the column's measured top safe area. That is the bar height where the column lays content under the bar, and 0 on Android.
  • On iOS 26, where the feed already gets a native contentInset of the bar height, it stays 0.
  • This value drives the existing list-header spacer, the empty and unavailable placeholders, the scroll-indicator inset and the first-send anchor offset.
  • The header-material scroll check adds the bar height only on the native-inset path, so the spacer does not count as a scroll.
• The doc comment on useContentTopInset now says it applies to solid bars too.

Scope and approval

Fixes pingdotgg/t3code#32884 Fixes pingdotgg/t3code#22543

Triaged via the automated issue flow. #22543 reports the sidebar half on its own.

Verification

• vp run check:changed passes on the head 08e1fb258a (format, lint, knip, typecheck, react compiler, tests beside the changed files).
• This is a visual bug, so the proof is device captures and no new test. Before is main at ca796d5211 (N1: 80e1e4d14d). After is eb39186ba6, f76e21be6c (comment-only on top), or 4980e33628, as each row says; the head 08e1fb258a only merges main with no apps/mobile changes. Both sides share the native fingerprint and Legend List 3.7.2. Main merged since eb39186ba6 changes only file preview, asset loading and the Android rail width (0 off Android) under apps/mobile. The changed inset paths are identical apart from comments.
• Environment: pool iOS simulators driven by agent-device, 1x capture pixels per point, default text size, fresh dev servers seeded with synthetic Replay (dev) threads. iPad (7th generation) iOS 18 1080×810 landscape, iPhone Xs iOS 18 / 18.6 375×812 portrait, iPad Pro 11-inch (M4) iPadOS 26.0 1210×834 landscape. Each comparison is cropped to the pane it covers, or has the status strip cropped and generated titles and timestamps masked identically on both sides. Diff0 marks every changed pixel; DiffT uses 5% fuzz.

Recordings:

• I1: before, tapping the hidden "Load earlier activity" loads nothing. After, the tap at 10.6 s loads the earlier page, and the first row sits fully below the header.
• I2: retry goes from error to loading to success.
• I3: before and after. Fill at 2 s, send at 6 s, then the reply, keyboard dismissed, and pans.
• N1: before and after. New task at 1 s, send at 23 s, refocus at 25–26 s, reply at 26–29 s. Send closes the keyboard on both sides.
• S5/S6b sidebar Search, dark: focus, results, no matches, clear, cancel. I4 sidebar hide/restore: row 07 stays in place. I5 Search jump: lands at about 122 pt before and 120 pt after, unchanged. All three are in run 3.

Evidence write-ups:

• run 1, run 2, run 3, run 4: source full screens and the remaining rows.
• N1.
• Comparison repairs: F2 F3 F5 F8 I2 G1 and S2 I3 N1, with their crop boxes, masks and scripts.
• Fixture matrix.

Seed and driver scripts: seed-rpc.mjs, driver.md, capture.py, seed.py, recapture-seed.mjs, repair-comparisons.py, repair-four-comparisons.py.

What else changed in the captures: only the moved content above. Inside each crop or mask, the following still differ:

• the status-bar clock;
• generated thread titles, Replay timestamps and durations;
• Expo dev-client overlays.

The recordings also carry touch markers and grey boxes over model labels. In the I1 before recording the inspector is 266 pt wide; after, it is 260 pt. Run 3's Search recordings show a Working counter only on the after side.

Not checked:

• Android. useContentTopInset returns 0 there, and the sidebar change is in the iOS-only branch.
• The compact iOS 26 send lifecycle. The feed keeps its native-inset path there with unchanged values, and G1 shows the glass inspector pixel-identical.