[ragojose]

What

Two viewport-mode bugs, both reported from the running app.

1. + / ⌘T in mobile mode snapped the window back to desktop. OnTabCreated ended with UpdateWindowForViewportMode(TabIsMobile(browser_id), …), and a brand-new tab is always desktop — so adopting it animated the 512×896 mobile shell back to the saved desktop frame and re-laid the chrome on every new tab. New tabs now inherit the outgoing active tab's viewport mode (the outgoing tab is still the active one during adoption; OnAfterCreated promotes the new browser only after adoption returns).

The overrides are applied a UI-thread turn later, via BroHandler::AdoptTabMobileEmulation. Calling ExecuteDevToolsMethod on a browser still inside its own OnAfterCreated is a deterministic SIGSEGV in CEF 151 (EXC_BAD_ACCESS on CrBrowserMain, OnAfterCreated → SetTabMobileEmulation → CefBrowserHostCToCpp::ExecuteDevToolsMethod) — hit while developing this, so the mode is recorded synchronously (the shell lays out from it in the same turn) and only the DevTools calls are deferred.

2. Activating a desktop tab from the mobile shell scrambled the tab strip. The activation spring moves pill frames through the animator; the window resize that follows re-laid the strip with plain frame sets, which do not stop an in-flight animation. Those pills kept springing to the targets computed for the 512pt strip inside a now-1200pt window and overlapped each other. Unanimated layouts now assign through the animator inside a zero-duration NSAnimationContext group, which both lands the frame and cancels the spring.

Measured pill geometry, 5 tabs, after switching from the mobile shell to a desktop tab:

	before	after
pills 1–3	28pt @468, 28pt @503, 110pt @539 (overlapping)	158pt @468, @634, @800
pills 4–5	158pt @967, @1133	158pt @967, @1133

Pills 4–5 were already correct because their slots didn't move on activation, so no animation was in flight for them — that asymmetry is what identified the cause.

Also in this branch

Uncommitted work that was already in the workspace, included here rather than stranded:

• Reading Mode crash gate moves to ImmersiveReadAnything; the previous ReadAnything name is not a base::Feature in CEF 151 (verified against the shipped framework), and Chromium silently ignores unknown disable-features names, so that switch was a no-op.
• Tab strip gains horizontal scrolling with the search control pinned at the trailing edge.

Testing

Driven through the accessibility API against a renamed copy of the build on an isolated profile, with page state read over CDP:

• + in mobile mode: window holds 512×896, toggles read Mobile, four consecutive new tabs, no crash reports.
• the inherited tab is genuinely emulated — navigating it reports W=390 DPR=2 TOUCH=5 UA=iphone.
• desktop unchanged: + from a desktop tab stays 1200×800.
• mobile ↔ desktop tab switches round-trip cleanly, 512×896 ↔ 1200×800, pills evenly spaced and stable both immediately and after settling; confirmed visually from a window capture.

🤖 Generated with Claude Code