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, 97 insertions, 0 deletions

diff --git a/rust/crates/timeline/src/track_element_update.rs b/rust/crates/timeline/src/track_element_update.rs
new file mode 100644
index 00000000..98395ab0
--- /dev/null
+++ b/rust/crates/timeline/src/track_element_update.rs
@@ -0,0 +1,97 @@
+use scene::{Element, SceneTracks, Track};
+
+pub fn find_track_in_scene_tracks<'a>(tracks: &'a SceneTracks, track_id: &str) -> Option<&'a Track> {
+    if tracks.main.id() == track_id {
+        return Some(&tracks.main);
+    }
+
+    tracks
+        .overlay
+        .iter()
+        .chain(tracks.audio.iter())
+        .find(|track| track.id() == track_id)
+}
+
+pub fn update_track_in_scene_tracks(
+    tracks: &SceneTracks,
+    track_id: &str,
+    update: impl Fn(&Track) -> Track,
+) -> SceneTracks {
+    if tracks.main.id() == track_id {
+        return SceneTracks {
+            main: update(&tracks.main),
+            ..tracks.clone()
+        };
+    }
+
+    if tracks.overlay.iter().any(|track| track.id() == track_id) {
+        return SceneTracks {
+            overlay: tracks
+                .overlay
+                .iter()
+                .map(|track| {
+                    if track.id() == track_id {
+                        update(track)
+                    } else {
+                        track.clone()
+                    }
+                })
+                .collect(),
+            ..tracks.clone()
+        };
+    }
+
+    if tracks.audio.iter().any(|track| track.id() == track_id) {
+        return SceneTracks {
+            audio: tracks
+                .audio
+                .iter()
+                .map(|track| {
+                    if track.id() == track_id {
+                        update(track)
+                    } else {
+                        track.clone()
+                    }
+                })
+                .collect(),
+            ..tracks.clone()
+        };
+    }
+
+    tracks.clone()
+}
+
+fn with_replaced_elements(track: &Track, elements: Vec<Element>) -> Track {
+    let mut next = track.clone();
+    *next.elements_mut() = elements;
+    next
+}
+
+pub fn update_element_in_scene_tracks(
+    tracks: &SceneTracks,
+    track_id: &str,
+    element_id: &str,
+    update: impl Fn(&Element) -> Element,
+    element_predicate: Option<&dyn Fn(&Element) -> bool>,
+) -> SceneTracks {
+    let update_in_track = |track: &Track| {
+        let elements = track
+            .elements()
+            .iter()
+            .map(|element| {
+                if element.base().id != element_id {
+                    return element.clone();
+                }
+                if let Some(predicate) = element_predicate
+                    && !predicate(element)
+                {
+                    return element.clone();
+                }
+                update(element)
+            })
+            .collect();
+        with_replaced_elements(track, elements)
+    };
+
+    update_track_in_scene_tracks(tracks, track_id, update_in_track)
+}