Three of the four locked items (1, 2, 4); item 6 (swipe-tabs) stays
deferred until server-side lyrics ingestion exists.
1. Dominant-color gradient backdrop. New album_color_extractor.dart
wraps the existing AlbumCoverCache: extracts the dominant color
via PaletteGenerator over the local file, caches in-memory keyed
by album_id. Top 55% of the screen carries the color (0.55 alpha
→ fs.obsidian) so controls below stay legible. AnimatedContainer
tweens the gradient across track changes.
2. Hero transition for cover art (mini bar → full screen). Stable
kPlayerCoverHeroTag (not media.id keyed) so the transition works
regardless of what's playing and isn't racy if media swaps mid-tap.
flightShuttleBuilder renders the destination's Hero widget for the
whole flight, which reads as a clean grow rather than a swap.
4. Crossfade on track change. AnimatedSwitcher around the album art,
title, and artist+album text block, all keyed by media.id so the
switcher fades between old and new on each track-change rebuild.
Pairs with the AnimatedContainer gradient so the whole "what's
playing" zone changes in lockstep.
palette_generator: ^0.3.3 added.
For #396 / #356 umbrella.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen
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