feat: GPUI desktop port foundation

- scene crate: full project/scene/element model, serde round-trip
  proven against the web SerializedProject shape
- transfer crate: .ocp zip container, cross-compat with web fflate
  archives proven in both directions
- storage crate: filesystem project store replacing IndexedDB,
  .ocp import/export
- media crate: ffmpeg-next 8 decoder (frames, audio, thumbnails,
  waveform summaries)
- playback crate: wall-clock anchored, frame-rounded playback clock
- gpu crate: native texture readback; compositor renders headless
  offscreen on Vulkan (spike test)
- flake devshell: rust toolchain, GPUI native deps, ffmpeg dev,
  bindgen clang args; GPUI hello-world builds
- port plan in notes/gpui-port.md

1 files changed, 120 insertions, 0 deletions

diff --git a/rust/crates/timeline/src/scenes.rs b/rust/crates/timeline/src/scenes.rs
new file mode 100644
index 00000000..8a7a5c4f
--- /dev/null
+++ b/rust/crates/timeline/src/scenes.rs
@@ -0,0 +1,120 @@
+use chrono::{DateTime, Utc};
+use scene::{Scene, SceneTracks};
+use time::MediaTime;
+
+use crate::placement::MAIN_TRACK_NAME;
+use crate::placement::track_factory::build_empty_track;
+use crate::types::TrackType;
+
+pub fn get_main_scene(scenes: &[Scene]) -> Option<&Scene> {
+    scenes.iter().find(|scene| scene.is_main)
+}
+
+pub fn ensure_main_scene(scenes: &[Scene], next_id: &mut dyn FnMut() -> String, now: DateTime<Utc>) -> Vec<Scene> {
+    if scenes.iter().any(|scene| scene.is_main) {
+        return scenes.to_vec();
+    }
+
+    let main_scene = build_default_scene(
+        next_id(),
+        next_id(),
+        "Main scene".to_string(),
+        true,
+        now,
+    );
+    let mut next = Vec::with_capacity(scenes.len() + 1);
+    next.push(main_scene);
+    next.extend(scenes.iter().cloned());
+    next
+}
+
+pub fn build_default_scene(
+    id: impl Into<String>,
+    main_track_id: impl Into<String>,
+    name: String,
+    is_main: bool,
+    now: DateTime<Utc>,
+) -> Scene {
+    Scene {
+        id: id.into(),
+        name,
+        is_main,
+        tracks: SceneTracks {
+            overlay: Vec::new(),
+            main: build_empty_track(
+                main_track_id,
+                TrackType::Video,
+                Some(MAIN_TRACK_NAME.to_string()),
+            ),
+            audio: Vec::new(),
+        },
+        bookmarks: Vec::new(),
+        created_at: now,
+        updated_at: now,
+    }
+}
+
+pub struct SceneDeleteCheck {
+    pub can_delete: bool,
+    pub reason: Option<String>,
+}
+
+pub fn can_delete_scene(scene: &Scene) -> SceneDeleteCheck {
+    if scene.is_main {
+        return SceneDeleteCheck {
+            can_delete: false,
+            reason: Some("Cannot delete main scene".to_string()),
+        };
+    }
+    SceneDeleteCheck {
+        can_delete: true,
+        reason: None,
+    }
+}
+
+pub fn get_fallback_scene_after_delete<'a>(
+    scenes: &'a [Scene],
+    deleted_scene_id: &str,
+    current_scene_id: Option<&str>,
+) -> Option<&'a Scene> {
+    if current_scene_id != Some(deleted_scene_id) {
+        return scenes.iter().find(|scene| Some(scene.id.as_str()) == current_scene_id);
+    }
+    get_main_scene(scenes)
+}
+
+pub fn find_current_scene<'a>(
+    scenes: &'a [Scene],
+    current_scene_id: &str,
+) -> Option<&'a Scene> {
+    scenes
+        .iter()
+        .find(|scene| scene.id == current_scene_id)
+        .or_else(|| get_main_scene(scenes))
+        .or_else(|| scenes.first())
+}
+
+pub fn get_project_duration_from_scenes(scenes: &[Scene]) -> MediaTime {
+    let Some(main_scene) = get_main_scene(scenes).or_else(|| scenes.first()) else {
+        return MediaTime::ZERO;
+    };
+
+    crate::calculate_total_duration(&main_scene.tracks)
+}
+
+pub fn update_scene_in_array(
+    scenes: &[Scene],
+    scene_id: &str,
+    update: impl Fn(&Scene) -> Scene,
+) -> Vec<Scene> {
+    scenes
+        .iter()
+        .map(|scene| {
+            if scene.id == scene_id {
+                update(scene)
+            } else {
+                scene.clone()
+            }
+        })
+        .collect()
+}