Report offline footage and recover automatically when media returns (#3161)

* 3118: report and recover offline footage consistently

* 3118: preserve manual reload and refresh data watch paths

* 3118: document availability and reload contracts

crates/render/src/disk_cache.rs

@@ -1004,6 +1004,11 @@ pub fn footage_salt_with(project: &effectcraft_project::Project, virtual_id: Opt
             hash_debug(&mut h, f);
             footage_stamp(&mut h, f, virtual_id);
         }
+        if let Some(proxy) = it.proxy.as_ref().filter(|p| p.enabled) {
+            h.write_u64(id.0);
+            hash_debug(&mut h, proxy);
+            footage_stamp(&mut h, &proxy.footage, virtual_id);
+        }
     }
     let v = h.finish();
     (v as u64) ^ ((v >> 64) as u64)

crates/render/src/footage.rs

@@ -99,20 +99,38 @@ pub trait FootageSource: Send + Sync {
     fn problem(&self, _footage: &Footage) -> Option<String> {
         None
     }
-    /// [`Self::problem`] of what `item` shows: its proxy's while Use Proxy shows the proxy
+    /// Missing files and [`Self::problem`] of what `item` shows: its proxy's while Use Proxy shows the proxy
     /// instead (the reason then says it is the proxy's), else the footage item's own. A
     /// composition has one only through its proxy.
     fn item_problem(&self, item: &effectcraft_project::Item) -> Option<String> {
         match item.proxy.as_deref().filter(|px| px.enabled && px.footage.has_video) {
-            Some(px) => self.problem(&px.footage).map(|why| format!("Proxy: {why}")),
+            Some(px) => {
+                missing_problem(&px.footage, "Use Set Proxy to locate the proxy file.").or_else(|| self.problem(&px.footage)).map(|why| format!("Proxy: {why}"))
+            }
             None => match &item.kind {
-                ItemKind::Footage(f) => self.problem(f),
+                ItemKind::Footage(f) => missing_problem(f, "Use File ▸ Dependencies ▸ Relink Missing Footage or Replace Footage.").or_else(|| self.problem(f)),
                 _ => None,
             },
         }
     }
 }
 
+/// A known offline source, without filesystem access while painting or querying.
+fn missing_problem(f: &Footage, remedy: &str) -> Option<String> {
+    (f.missing && !f.path.is_empty() && f.kind != effectcraft_project::FootageKind::Data).then(|| format!("Missing footage: {}. {remedy}", f.path))
+}
+
+/// Inventory warning, including an unused proxy or an original currently replaced by a proxy.
+/// Viewer warnings instead use `item_problem`, which follows the active render source.
+pub fn missing_item_problem(item: &effectcraft_project::Item) -> Option<String> {
+    if let ItemKind::Footage(f) = &item.kind
+        && let Some(why) = missing_problem(f, "Use File ▸ Dependencies ▸ Relink Missing Footage or Replace Footage.")
+    {
+        return Some(why);
+    }
+    item.proxy.as_ref().and_then(|p| missing_problem(&p.footage, "Use Set Proxy to locate the proxy file.")).map(|why| format!("Proxy: {why}"))
+}
+
 /// A render's view of a [`FootageSource`] whose frame reads can be called off with `cancel`
 /// (a viewer frame nobody waits for any more, #329). Every read goes through
 /// [`FootageSource::cancellable`] on its own, so reads made for this render on another thread

crates/render/src/lib.rs

@@ -46,7 +46,7 @@ mod opts;
 mod pipeline;
 
 pub use accel::{Accelerator, Backend, FxStep, FxTarget};
-pub use footage::{CancellableFootage, FloatCurve, FootageSource, NoFootage, is_vector_footage};
+pub use footage::{CancellableFootage, FloatCurve, FootageSource, NoFootage, is_vector_footage, missing_item_problem};
 pub use frames::{
     adaptive_samples, blend_frames, cineon_frame, content_bounds, extended_region, field_frame, frame_position, frame_size, interpret_pixels, kurbo_path,
     render_frame, roi_inside,