feat(import): say which fields differ, and stop offering to apply nothing

A row marked "edited" or "conflict" gave no way to tell what actually
differs, so a resource that drifted from the file — however it drifted —
reads as an unexplained accusation. The plan now carries the field names
the source and the local copy disagree on, and the row's tooltip lists
them.

The preview's primary button also read "Apply" when the current selection
would change nothing. It now reads "Done", since committing an empty
selection only records the decisions made in the preview.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/yaak/src/import.rs

@@ -842,6 +842,7 @@ fn merge_with_linked_source(
                 selected,
                 resolution,
                 reason,
+                changed_fields: Vec::new(),
             };
 
             // Nothing can be created inside a folder that isn't imported, so it starts unchecked
@@ -870,13 +871,15 @@ fn merge_with_linked_source(
                 return Ok(());
             }
 
-            let incoming = serde_json::to_value(&any)?;
-            let current = current_models.get(&planned_id).cloned().unwrap_or_default();
+            let incoming = comparable(serde_json::to_value(&any)?);
+            let current = comparable(current_models.get(&planned_id).cloned().unwrap_or_default());
             let (source_changed, local_changed) = match recorded_hash(row) {
-                Some(hash) => (content_hash(incoming) != hash, content_hash(current) != hash),
+                Some(hash) => {
+                    (hash_comparable(&incoming) != hash, hash_comparable(&current) != hash)
+                }
                 // Without a recorded version, all that can be told is whether the two sides differ
                 None => {
-                    let differs = comparable(incoming) != comparable(current);
+                    let differs = incoming != current;
                     (differs, differs)
                 }
             };
@@ -891,7 +894,9 @@ fn merge_with_linked_source(
                     Some(ImportConflictResolution::KeepMine),
                 ),
             };
-            items.push(item(action, selected, resolution, None));
+            let mut planned = item(action, selected, resolution, None);
+            planned.changed_fields = changed_fields(&incoming, &current);
+            items.push(planned);
             Ok(())
         };
 
@@ -946,6 +951,7 @@ fn merge_with_linked_source(
             selected: false,
             resolution: None,
             reason: None,
+            changed_fields: Vec::new(),
         });
     }
 
@@ -965,6 +971,7 @@ fn create_only_items(plan: &ImportPlan) -> Vec<ImportPlanItem> {
             selected: true,
             resolution: None,
             reason: None,
+            changed_fields: Vec::new(),
         });
     };
     for v in &plan.resources.folders {
@@ -1014,10 +1021,29 @@ const CONTENT_HASH_VERSION: &str = "v1:";
 /// Identifies a resource's content well enough to tell "changed since the last import" from
 /// "unchanged", without keeping a copy of every imported resource around.
 fn content_hash(value: Value) -> String {
-    let canonical = serde_json::to_string(&sorted_keys(comparable(value))).unwrap_or_default();
+    hash_comparable(&comparable(value))
+}
+
+fn hash_comparable(value: &Value) -> String {
+    let canonical = serde_json::to_string(&sorted_keys(value.clone())).unwrap_or_default();
     format!("{CONTENT_HASH_VERSION}{:x}", Sha256::digest(canonical.as_bytes()))
 }
 
+/// The fields two comparable forms disagree on, so a preview row can explain itself.
+fn changed_fields(incoming: &Value, current: &Value) -> Vec<String> {
+    let (Some(incoming), Some(current)) = (incoming.as_object(), current.as_object()) else {
+        return Vec::new();
+    };
+    incoming
+        .keys()
+        .chain(current.keys())
+        .collect::<BTreeSet<_>>()
+        .into_iter()
+        .filter(|key| incoming.get(*key) != current.get(*key))
+        .cloned()
+        .collect()
+}
+
 /// A hash written by a version this build doesn't understand says nothing about the resource.
 fn recorded_hash(row: &ImportSourceResource) -> Option<&str> {
     let hash = row.content_hash.as_deref()?;
@@ -2079,6 +2105,7 @@ mod tests {
         let nested = item_by_name(&plan, "Nested Request");
         assert_eq!(nested.action, ImportPlanAction::KeepLocal);
         assert!(!nested.selected);
+        assert_eq!(nested.changed_fields, vec!["url".to_string()], "the preview names the edit");
         let extra = item_by_name(&plan, "Extra Request");
         assert_eq!(extra.action, ImportPlanAction::Create);
         assert!(extra.selected);