feat: add same-window compact playback with magnetic snapping

README.md

@@ -22,6 +22,10 @@ The layout follows [IINA's video-first window](https://iina.io/img/screenshot.pn
 
 Opening video fits the window to its display aspect ratio, including non-square pixels, and constrains subsequent window resizing. Fullscreen retains the normal letterboxed renderer; audio-only playback and close release the aspect constraint. Extreme ratios that cannot fit both the screen and usable controls keep a freely resizable letterboxed window.
 
+**Compact mode** uses the same window, Metal view, and playback session—not a second window or macOS system PiP. Use **⌃⌘P** or **Playback Actions → Enter Compact Mode**. It starts at the current screen's bottom-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.
+
+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 and remembers its toggle across launches. 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.
+
 | Key | Action |
 |---|---|
 | `K` / `Space` | Toggle playback |
@@ -37,12 +41,12 @@ Single-key shortcuts apply only to the playback window and do not intercept text
 
 Frame stepping uses decoded presentation timestamps, not an average-FPS time offset, including variable-frame-rate video and reordered B-frames. Steps start from the displayed frame, stop at the first/last frame, and keep the timeline paused. Consecutive same-direction repeats share one counted queue entry without skipping frames or reordering seeks/direction changes. The last presented image remains visible during decoder preroll and queued steps; the progress thumb follows each authoritative stepped position. Opening/closing media still clears the old image. Audio-only files disable stepping; normal playback resumes with audio synchronized to the selected frame.
 
-- Existing shortcuts remain: **⌘O** opens files, **←/→** seeks five seconds, **↑/↓** adjusts volume by five percent, **⌃⌘F** toggles fullscreen, and **Esc** leaves fullscreen. Double-clicking video also toggles fullscreen.
+- Existing shortcuts remain: **⌘O** opens files, **←/→** seeks five seconds, **↑/↓** adjusts volume by five percent, **⌃⌘F** toggles fullscreen, and **Esc** leaves fullscreen. Double-clicking normal-mode video also toggles fullscreen.
 - The timeline slider seeks on release and holds the requested position until queued seeking finishes. Both slider tracks span the native thumb-center travel range; the orange fill ends at the current volume thumb center. The volume thumb is opaque light gray.
-- **Single-click video:** hide controls. Mouse movement reveals them; they fade after 2.5 seconds, including while paused. Hovering the titlebar/controller, dragging, seeking, an inactive window, errors, or VoiceOver keep them visible.
+- **Single-click normal-mode video:** hide controls. Mouse movement reveals them; they fade after 2.5 seconds, including while paused. Hovering the normal titlebar or either controller, dragging, seeking, an inactive normal-mode window, errors, or VoiceOver keep them visible. Compact controls can fade while another app is active; hovering its video reveals them without hiding the desktop cursor.
 - Click the right-hand time label to switch between total and remaining time. The titlebar pin keeps the window on top.
 
-Only implemented actions have controls; there are no placeholder playlist, subtitle, picture-in-picture, or settings buttons. Layout and interaction references: IINA v1.5.0's [floating controller](https://github.com/iina/iina/blob/v1.5.0/iina/OSCFloatingView.swift), [preferences](https://github.com/iina/iina/blob/v1.5.0/iina/Preference.swift), and [titlebar](https://github.com/iina/iina/blob/v1.5.0/iina/Titlebar.swift).
+Only implemented actions have controls; there are no placeholder playlist, subtitle, or settings buttons. Layout and interaction references: IINA v1.5.0's [floating controller](https://github.com/iina/iina/blob/v1.5.0/iina/OSCFloatingView.swift), [preferences](https://github.com/iina/iina/blob/v1.5.0/iina/Preference.swift), and [titlebar](https://github.com/iina/iina/blob/v1.5.0/iina/Titlebar.swift).
 
 ## Where to change things
 
@@ -50,6 +54,7 @@ Only implemented actions have controls; there are no placeholder playlist, subti
 - `Sources/Core/player.cpp`: single demux/decode worker, bounded buffers, timestamps, audio-master synchronization, paused previews, exact frame stepping, decoder/resampler drain, seeking, errors, and shutdown. A seek stops output and flushes all old timeline state before resuming.
 - `Sources/Core/output.hpp` and `Sources/macOS/Output.mm`: native output contract, allocation-free/nonblocking Core Audio callback and bounded audio ring, latency-aware presentation clock, retained frame mailbox, and Metal YUV conversion. The view can outlive the player safely.
 - `Sources/App/TerebiApp.swift`: MainActor state polling, file panel/Finder/drop handling, autoplay, video host, AppKit glass and native slider cells, floating controls, visibility, video-fitted sizing, and native window integration. The shared `PlayerModel.open` path enqueues play after an accepted open, on the new file's command timeline; the C interface still opens paused for callers that need explicit playback control.
+- `Sources/App/CompactWindow.swift`: same-window compact geometry, saved normal window state, asynchronous fullscreen transitions and failure recovery, all-Spaces/floating behavior, magnetic edge snapping, and its persisted preference.
 - `Makefile`: compiler/linker commands and app bundle construction. No generated Xcode project or additional build dependency.
 
 ## Runnable check
@@ -62,6 +67,8 @@ Generates short fixtures and exercises the real playback interface and native ou
 
 `make check-audio` runs just the audio-quality check. A check-only hook captures actual Core Audio callback PCM into preallocated storage and compares every sample against FFmpeg's reference output for PCM/AAC, 44.1/48 kHz, and coarse container timestamps. It verifies that repeated forward/backward stepping stays silent and that resumed audio matches the exact selected-frame PCM suffix. It also checks fractional gain, silent muted startup, smooth live volume changes, and unchanged playback completion. A separate gapped fixture verifies that real timestamp gaps remain silent. Release builds contain no capture hook.
 
+`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, isolated preference persistence, 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.
+
 Continuous audio uses resampled sample counts for its output timeline; packet timestamp quantization and rounded resampler delay must not insert silence or drop samples between blocks.
 
 Volume persists across open, seek, and close. Live gain changes ramp over five milliseconds without callback allocation or locking; a stopped output adopts the requested gain before playback starts, so muted startup cannot leak audio.