The merge job and its page: a selection to a panorama DNG, confirmed first

dr_ui::merge is the orchestration with no interface in it: decode each
frame to sensor data and build its graph as a session would (orientation,
lens profile); render each through the camera-space tap at proxy size and
detect keypoints there, so the alignment is measured in the undistorted
frame the tiles are rendered in; align; solve one gain per frame from the
proxies' overlaps; draw the aligned set in colour for the page; then wait.
Nothing is written until a Decision arrives (FR-MRG-1). The merge writes
a linear DNG through the outbox with a destination record, so the drain
puts it beside its sources on a folder library and a server alike, and
the library rescans (FR-MRG-3).

merge.slint is the page, on the import page's model: the alignment
table with a failed frame named on its row and the button held off
(FR-MRG-5), the preview, the projection choice, Stop and Back. A
"Merge to panorama" button joins the grid's selection bar at two frames.

Headless, the example produces the fixture's 22 993 x 5 980 DNG in 45 s
on the reference desktop, exposures balanced across the stop of drift.

ui/dr-ui/src/lib.rs

@@ -46,6 +46,8 @@ mod library_ui;
 mod live_style;
 mod masks_ui;
 pub mod memory;
+pub mod merge;
+mod merge_ui;
 mod net_runtime;
 mod peaking;
 mod place;
@@ -1542,6 +1544,35 @@ pub fn run(paths: Vec<PathBuf>) -> Result<()> {
         // through (`dr_plat::imports_supported`).
         window.set_import_supported(dr_plat::imports_supported());
 
+        // TRACES: FR-MRG-1
+        {
+            let merge = merge_ui::MergeController::new(activity.clone());
+            let library_for_sources = library.clone();
+            let collections_for_sources = collections.clone();
+            let library_for_context = library.clone();
+            let library_for_done = library.clone();
+            merge_ui::wire(
+                &window,
+                merge,
+                gpu.clone(),
+                move || library_for_sources.export_sources(&collections_for_sources.selected()),
+                move || {
+                    let conn = library_for_context.session()?;
+                    Some(merge_ui::Context {
+                        outbox: export::outbox_dir(&conn.account),
+                        conn,
+                    })
+                },
+                move |w| {
+                    // Staged beside its sources: upload it now rather than
+                    // on the next sync pass, then look for it, exactly as an
+                    // import does.
+                    drain_outbox(&library_for_done);
+                    w.invoke_library_rescan();
+                },
+            );
+        }
+
         let import = import_ui::ImportController::new(settings.clone(), activity.clone());
         let library_for_context = library.clone();
         let weak = window.as_weak();