UI hooks

Scripts cannot draw Slint widgets, so packages reach Vivi's UI through script messages:

Need	Use
Short status / confirmation	`vivi-toast <text>`
Pairing link or code	`vivi-qr <title> <text> [caption]`
Folder chooser	`vivi-pick-folder <id> <key>`
Seek-bar hover previews	write `seek-NN.jpg` and send `vivi-preview-frames <dir>`
Chapter pictures in the Chapters tab	write `chapter-N.jpg` and send `vivi-chapter-thumbs <dir>`
Buttons in Settings	`action` settings
Overlay text	`mp.osd_message` / `mp.create_osd_overlay` (drawn under Vivi's UI)
Keys	`mp.add_forced_key_binding`

Need a widget that does not exist yet? Open an issue in Loafer19/vivi: new hooks are added as script messages.

Built-in (Rust) plugins

Features with rich UI (visualizer, Skip Intro, Lyrics, Subtitle Search, Auto-tagger, Free Music, Network Streams) are compiled into Vivi in src/plugins/. Each implements the Plugin trait and is listed in plugins::builtin(); the Registry calls the enabled ones on the UI thread:

Hook	When
`enable(cx)` / `disable(cx)`	Switched on / off (and at startup).
`file_loaded(cx)`	mpv loaded a new file.
`tick(cx)`	Every 100 ms; poll worker-thread channels here.
`setting_changed(cx, key)`	A setting changed (already saved).
`command(cx, name, args)`	An action button or a Slint `plugin-command(id, name, args)` callback.

Ctx gives cx.app (the Slint window), cx.player (mpv), cx.get / cx.flag / cx.set for settings and cx.toast. Hooks run on the UI thread: do network and disk work on a thread and send results through a channel. These live in the vivi repository and also need an entry in plugins/index.json here (kind = "builtin").