Reload Footage shows new pixels and keeps Photoshop layers; Reload Footage Changed on Disk

Reload Footage (Cmd+Alt+L) updated an item's metadata but left the media
pool's decoded frames and the layer cache in place, so the old image kept
rendering until Edit > Purge. It also replaced the footage with a probe of
the merged document, so a Photoshop layer item lost its layer and its
Retain Layer Sizes bounds.

Reload now re-reads only what the file decides (size, a movie's duration,
streams and frame rate, codec, a data file's text), keeps the layer or
page and the interpretation, finds a Photoshop layer again by name, and
makes the media layer forget the file (FootageSource::forget, which also
drops the EXR aux-channel cache) and clears the layer cache.

Settings > Import > Reload Footage Changed on Disk (on by default): the
desktop app stamps footage files (size + modification time) on a worker
thread every two seconds and when the window comes back to the front, and
reloads what changed. Not an undo step and it doesn't modify the project;
a file still being written is retried on the next check.
footage.reloadChanged runs one check (CLI, MCP, agents).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/lib.rs

@@ -16,6 +16,7 @@ pub mod commands;
 pub mod config;
 pub mod demo;
 pub mod footage_check;
+pub mod footage_reload;
 pub mod guard;
 pub mod history;
 pub mod jobs;
@@ -101,6 +102,13 @@ pub trait Services: Send + Sync {
     fn exists(&self, path: &str) -> bool {
         std::path::Path::new(path).exists()
     }
+    /// A file's size and modification time (nanoseconds since 1970), to notice that it changed
+    /// on disk (Settings ▸ Import ▸ Reload Footage Changed on Disk); `None` when it can't be read.
+    fn stamp(&self, path: &str) -> Option<(u64, u128)> {
+        let meta = std::fs::metadata(path).ok()?;
+        let modified = meta.modified().ok()?.duration_since(std::time::UNIX_EPOCH).ok()?;
+        Some((meta.len(), modified.as_nanos()))
+    }
     /// Keep a file the app made for itself (footage extracted from a template): like
     /// [`Services::write_file`], creating its folder, but never offered as a download (web: it
     /// goes to browser storage only).
@@ -459,6 +467,11 @@ pub struct Session {
     /// event loop (the desktop app) turn this on; headless sessions run `footage.check` when
     /// they want it.
     pub check_footage_on_open: bool,
+    /// Each footage file's size and modification time when last seen (Settings ▸ Import ▸
+    /// Reload Footage Changed on Disk, [`footage_reload`]).
+    pub footage_stamps: std::collections::HashMap<String, footage_reload::Stamp>,
+    /// The stamps being taken on a worker thread ([`footage_reload::start_scan`]).
+    pub footage_scan: Option<footage_reload::Scan>,
 }
 
 /// A thumbnail render ([`Session::thumbnail_job`]): (width, height, RGBA8).
@@ -544,6 +557,8 @@ impl Default for Session {
             next_task_id: 1,
             learn: None,
             check_footage_on_open: false,
+            footage_stamps: Default::default(),
+            footage_scan: None,
         }
     }
 }