feat: animate compact window transitions

README.md

@@ -190,6 +190,8 @@ Opening video fits the window to its display aspect ratio, including non-square
 
 **Compact mode** uses the same window, Metal view, and playback session—not a second window or macOS system PiP. Use the PiP-shaped button in the normal playback controls, **⌃⌘P**, or **Playback Actions → Enter Compact Mode**. The compact-mode button replaces the fullscreen button; fullscreen remains available through its menu, keyboard shortcuts, and double-clicking normal-mode video. Compact mode starts at the current screen's top-right corner with a 16-point inset and a preferred width of 320 points, preserving display aspect where usable screen bounds and the 160 × 90-point minimum allow; extreme ratios retain letterboxing. Compact mode floats above ordinary windows, joins all Spaces, and is configured to join eligible other-app fullscreen spaces and Stage Manager sets. Small hover controls provide play/pause, restore, and Playback Actions; keyboard playback controls remain available.
 
+Entry and restoration animate the same window's position and size over **250 ms** with ease-in/ease-out timing while normal and compact controls cross-fade; playback and the Metal view stay in place. macOS **Reduce Motion** disables both animations. Rapid toggles keep the latest destination and finish the current native frame animation before changing direction; native fullscreen transitions are also serialized. Media close, errors, shutdown, and explicit fullscreen handoff restore immediately rather than leave a frame animation pending.
+
 Drag the compact video to move the window; on release, each axis snaps independently when within 24 points of an inset usable-screen edge. **Snap to Screen Edges** is enabled by default, configurable with `[ui].compact_snap_to_edges`, and its toggle is session-only. Disabling snapping permits free placement. Exiting compact mode restores the previous normal geometry and window behavior, including keep-on-top; entry from fullscreen waits for the native exit animation, and restoring that session returns to fullscreen. Double-clicking compact video also restores the previous mode. Video replacement updates the compact aspect; audio-only replacement, playback errors, and closing the file leave compact mode. Closing the window still quits the app.
 
 Default shortcuts and their explicit action names are listed in **Configuration**. Bindings apply only to the playback window and do not intercept text editing, file/URL dialogs, plain Tab navigation, or VoiceOver's Control+Option commands. Configured modifier combinations work in playback. Holding a playback/window/settings key performs it once; seek, volume, and frame-step keys may repeat. Player menus show the first configured chord and use the same explicit actions rather than retaining hidden fixed player shortcuts; all configured chords work from playback. Return/Space navigation in an open menu activates its selected action.
@@ -221,7 +223,7 @@ Playback terms are defined in [CONTEXT.md](CONTEXT.md).
 - `Sources/App/AutomaticQuality.swift`: clock-injected quality decisions using reserve/stall hysteresis, stepwise resolution choices, cooldown and extraction-failure backoff. Ordinary state revisions do not reset health; source/seek/pause transitions do.
 - `Sources/App/PlaybackProgress.swift`: local per-video position persistence and canonical file identities, using injectable UserDefaults. The player model checkpoints authoritative positions, supplies saved YouTube positions as backend open intent, and queues local restoration against the ready source.
 - `Sources/App/SystemPlaybackControls.swift`: native remote-command registration, main-thread dispatch, Now Playing publication, seekability gating, and target cleanup.
-- `Sources/App/CompactWindow.swift`: same-window compact geometry, saved normal window state, asynchronous fullscreen transitions and failure recovery, all-Spaces/floating behavior, and magnetic edge snapping with a session-only toggle.
+- `Sources/App/CompactWindow.swift`: same-window compact geometry, saved normal window state, serialized frame/fullscreen animations with cancellation, Reduce Motion and failure recovery, all-Spaces/floating behavior, and magnetic edge snapping with a session-only toggle.
 - `Sources/App/YouTubeResolver.swift`: YouTube URL and metadata validation, strict bundled yt-dlp/Deno discovery, capped-default or explicit-resolution SDR selection, playable resolution discovery and headers, bounded nonblocking process output, sanitized extraction errors, and request-local cancellation.
 - `Sources/CLI/PlayerCommand.swift` and `Sources/CLI/TerebiCLI.swift`: command-line validation/help and native application discovery/launching. Fresh instances receive media/config/reporting startup arguments in one launch; default reuse delivers the selected URL to an existing app. The app owns Apple events to prevent SwiftUI's default external-document routing from replacing its singleton window.
 - `Sources/Launcher/FFmpegRuntime.swift` and `Sources/App/Bootstrap.swift`: shared bundled-library preflight and the app's FFmpeg-independent entrypoint. The bootstrap loads the player library and calls its exported `terebi_app_main` entry point without replacing the executable, consuming initial launch events, or losing macOS app identity. `Contents/Resources/ffmpeg-libraries.txt` records the five versioned library filenames relative to `Contents/Frameworks`.
@@ -242,6 +244,8 @@ Generates short fixtures and exercises the real playback interface and native ou
 
 `make check-window` runs the compact-mode check, also included in `make check`. It exercises magnetic thresholds/corners, negative-origin screens, portrait/extreme aspect bounds, configured/session-only snapping, actual hidden-window entry/resizing/snapping/restoration, view-host identity, keyboard eligibility, and a replay of AppKit's fullscreen-failure lifecycle. It requires a graphical macOS session but does not display windows or play audio. Visible fullscreen transitions, cross-Space/Stage Manager behavior, and hover/drag usability still require a check in the app.
 
+The native window check also covers queued entry/exit reversals, exact snapshot recovery, urgent nonanimated restoration, close/reattachment ignoring stale completions, and injected Reduce Motion. Animation smoothness and control cross-fades still need visual verification in the app.
+
 `make check-config` checks isolated XDG/fallback paths, missing-file defaults without creation, partial/quoted/commented nested TOML, invalid syntax/types/keys/UTF-8, shortcut replacement/unbinding, chord normalization, inverse-pair sharing and unrelated conflicts, invalid action/quality names, duplicate keys, read errors, explicit path delivery, `--no-config` bypass, and unchanged file bytes/session reset. It needs neither FFmpeg nor a graphical session and never reads the user's configuration.
 
 `make check-youtube` checks URL/metadata/header trust boundaries, resolution choices and the default cap, real subprocess output, bounded pipe draining, cancellation, request isolation, and damaged/moved helper discovery using isolated fixtures. It also runs the actual bundled extractor against offline metadata to verify 1080p priority over extractor preferences, combined-stream selection, lower-resolution fallback, and explicit 4K; no external network access is required.