feat(ui): redesign the desktop screen share picker

[renefloor]

Redesigns the desktop screen-share picker onto the design system, and stops it hammering the platform while it is open.

Figma: Screen Share Modal

Why

The old picker was a raw Material AlertDialog with a Material TabBar, styled from the pre-design-system StreamVideoTheme.colorTheme, with a hard-coded 640×560 body and Colors.blueAccent selection borders.

It was also slow. ScreenSelectorStateNotifier ran a Timer.periodic(2s) calling updateSources() for as long as the dialog was open. Every tick made the platform re-enumerate every screen and window and re-capture a full-resolution bitmap of each — getSources was called without a thumbnailSize. Each thumbnail event then allocated a new state object, which rebuilt the entire dialog through one top-level ValueListenableBuilder, and called setState on the tile, re-decoding an uncapped Image.memory on the UI isolate. With ~30 windows open that is 30 full-tree rebuilds and 30 full-res decodes every two seconds.

On top of that, the notifier was disposed only in the Cancel and Share handlers. Dismissing with Esc or a tap outside leaked the notifier, its three subscriptions and the timer — which then kept re-enumerating sources for the rest of the app's life, stacking one more per open.

What changed

Loading. ScreenShareSourceController replaces ScreenSelectorStateNotifier. It reads both source types in a single getSources call when the picker opens, and again only when the refresh button in the header is pressed. No timer, no onAdded/onRemoved/onThumbnailChanged subscriptions. It asks for 480×300 thumbnails instead of whatever the platform defaults to. Switching tabs is now a filter over already-loaded state rather than a wipe-and-refetch. The dialog owns the controller through a StatefulWidget, so it is disposed whichever way the dialog goes away.

Design. StreamModalDialog + showStreamModalDialog (header with title and actions, footer, StreamBlurScrim barrier) and StreamTabBar join src/widgets/design_system_candidates/ — stream_core_flutter ships none of them yet. StreamScreenShareSelector is the grid, StreamScreenShareThumbnail one tile, and StreamScreenShareSelectorThemeData restyles them.

A tile's selection border paints as a foregroundDecoration, so going from the unselected 1px to the selected 2px never resizes the tile.

Breaking

TabbedScreenSelectWidget, ThumbnailGrid, ScreenSelectorStateNotifier and ScreenSelectorState are gone; ScreenShareThumbnailWidget is StreamScreenShareThumbnail. showDefaultScreenSelectionDialog and StreamScreenShareButton.desktopScreenSelectorBuilder keep their signatures, so the common path needs no change. The dogfooding custom-selector example is ported.

Tests

• ScreenShareSourceController: one getSources for both types, a capped thumbnailSize, updateSources never called, a tab switch that reloads nothing, refresh that reloads once, a dropped selection, a failed load.
• StreamScreenShareSelector and showDefaultScreenSelectionDialog: tab contents, selection, the empty state, no polling over ten seconds, and picking a source through the real entry point.
• StreamTabBar and StreamModalDialog: indicator, tap reporting, header and footer slots, close button, dismissal through the scrim.
• Goldens for the whole modal and for both tabs, in light and dark. Snapshotted inline rather than through the route — the CI capture path drops Overlay content.

🤖 Generated with Claude Code

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[codecov]

Codecov Report

❌ Patch coverage is 93.13187% with 25 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (v2@ad336b1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
.../lib/src/screen_share/desktop_screen_selector.dart	90.69%	8 Missing ⚠️
.../theme/components/screen_share_selector_theme.dart	53.33%	7 Missing ⚠️
...c/screen_share/screen_share_selector_defaults.dart	93.02%	3 Missing ⚠️
...zations/stream_video_flutter_localizations_nl.dart	0.00%	2 Missing ⚠️
...c/screen_share/screen_share_source_controller.dart	96.82%	2 Missing ⚠️
...dgets/design_system_candidates/stream_tab_bar.dart	95.23%	2 Missing ⚠️
...ideo_flutter/lib/src/theme/stream_video_theme.dart	85.71%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##             v2    #1342   +/-   ##
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  Coverage      ?   32.15%           
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  Files         ?      378           
  Lines         ?    28992           
  Branches      ?        0           
=====================================
  Hits          ?     9321           
  Misses        ?    19671           
  Partials      ?        0           

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