Probe and compile for a package's models, not only the user's

`inference::init` listed the models from the user's shared directory
alone, while the app loads them from there or from the package's
`/usr/share/darkroom/models`. On a fresh package install the probe found
"no model to probe with", stayed on the CPU, and compiled nothing. Both
now resolve each file with the same search, `library::shared_model`.

The PKGBUILD names the ONNX Runtime packages as optional dependencies,
since the app loads one from /usr/lib if present.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/inference.rs

@@ -19,23 +19,26 @@ use dr_types::FaceDetector;
 /// fingerprints the model files and a probe before they land would be a
 /// probe of nothing.
 pub fn init(runtime_dirs: Vec<PathBuf>) {
-    let dir = crate::library::shared_face_models_dir();
-    let mut models: Vec<(Role, PathBuf)> = FaceDetector::ALL
+    // Each file where the app will actually load it from — the user's
+    // shared directory, else the package's — so a fresh install with models
+    // only under `/usr/share` probes and compiles for them rather than
+    // finding nothing and settling on the CPU.
+    let mut wanted: Vec<(Role, &str)> = FaceDetector::ALL
         .iter()
-        .map(|d| (Role::Detector, dir.join(d.file_name())))
+        .map(|d| (Role::Detector, d.file_name()))
+        .collect();
+    wanted.extend([
+        (Role::Embedder, "arcface_mbf_b1.onnx"),
+        (Role::Scene, "yolo26s-sem-ade20k.onnx"),
+        (Role::Landmarks, crate::library::LANDMARK_MODEL),
+        (Role::EyeClassifier, crate::library::EYE_MODEL),
+        (Role::EyeClassifier, crate::library::SUNGLASSES_MODEL),
+        (Role::Inpainter, crate::library::INPAINT_MODEL),
+    ]);
+    let models: Vec<(Role, PathBuf)> = wanted
+        .into_iter()
+        .filter_map(|(role, name)| Some((role, crate::library::shared_model(name)?)))
         .collect();
-    models.push((Role::Embedder, dir.join("arcface_mbf_b1.onnx")));
-    models.push((Role::Scene, dir.join("yolo26s-sem-ade20k.onnx")));
-    models.push((Role::Landmarks, dir.join(crate::library::LANDMARK_MODEL)));
-    models.push((Role::EyeClassifier, dir.join(crate::library::EYE_MODEL)));
-    models.push((
-        Role::EyeClassifier,
-        dir.join(crate::library::SUNGLASSES_MODEL),
-    ));
-    if let Some(p) = crate::library::inpaint_model() {
-        models.push((Role::Inpainter, p));
-    }
-    models.retain(|(_, p)| p.is_file());
 
     dr_inference_engine::init(dr_inference_engine::Config {
         runtime_dirs,
@@ -75,12 +78,13 @@ pub fn user_runtime_dir() -> PathBuf {
 /// Which form the current backend loads `detector` in, given the files on
 /// this device — the fact `faces.model_id` has to carry (§7).
 ///
-/// Reads the shared directory only. An account-private model directory can
-/// override the file `library::face_models` loads, but not which form the
-/// backend wants, and the int8 sibling is something a packager ships, not
-/// something a user drops in.
+/// Reads the shared and system directories only. An account-private model
+/// directory can override the file `library::face_models` loads, but not
+/// which form the backend wants, and the int8 sibling is something a
+/// packager ships, not something a user drops in.
 pub fn detector_form(detector: FaceDetector) -> Form {
-    let canonical = crate::library::shared_face_models_dir().join(detector.file_name());
+    let canonical = crate::library::shared_model(detector.file_name())
+        .unwrap_or_else(|| crate::library::shared_face_models_dir().join(detector.file_name()));
     dr_inference_engine::resolve_model(Role::Detector, &canonical).1
 }