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Resuming the app with a busy channel open stalled for several frames (149, 136, 109 and 102 ms on an iPhone 12 mini), because every visible message re-parsed its markdown, repeatedly. The app widget rebuilds on every lifecycle change, and each rebuild created new light and dark `ThemeData`. A new `ThemeData` never equals the previous one, so `MaterialApp` animated between two identical themes for its full theme transition. Each frame of that animation produced a new markdown theme, and every mounted message re-parsed its markdown in response (`_MdWidgetState.didChangeDependencies` and `didUpdateWidget`). In a 15 s resume on a large channel that re-parse took 373 ms of main-isolate time. The themes are now built only when the community accent changes, so a lifecycle rebuild keeps the same theme objects and starts no transition. ### Validation - Added test: `an app rebuild keeps its themes and markdown theme` rebuilds the app and checks that the theme and the markdown theme stay identical. It fails without the change. - Full mobile suite: only the known failures that also fail on main (notification toggle, push bootstrap, push bridge, push lease revocation outbox). - Automated simulator run (iPhone 17 Pro, debug build): opened a channel with markdown messages, backgrounded and resumed the app several times, and switched between light and dark appearance while the app was open. Messages render, resume works, and the app follows appearance changes live. A channel's long-press action sheet keeps its light background after a switch to dark mode on both this build and main, so that is unrelated to this change. - Profile evidence (iPhone 12 mini, Profile build, before the change): the stalls and re-parse samples above came from a resume with a large channel open. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Signed-off-by: Tom Brow <tomb@squareup.com> Co-authored-by: Tom Brow <tomb@squareup.com> Co-authored-by: studio <dc2fc481343672df31a689840c09299972e704dac592e0da6f18486646a7ee3e@buzz.block.builderlab.xyz>