Format the tree the way the gate asks for it

`cargo fmt --check` is a required step and had drifted across 45 files. Most of
it arrived this week: several operations were written in parallel worktrees and
merged by hand, and a hand-merge resolves conflicts without ever running the
formatter over the result.

No behaviour changes — this is `cargo fmt --all` and nothing else, kept as its
own commit so the next reader can skip it wholesale rather than search it for
one that matters.

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

core/dr-segment/src/prior.rs

@@ -142,7 +142,11 @@ impl Membership {
 
     /// The instance a region belongs to, if any.
     pub fn instance_of(&self, region: u32) -> Option<usize> {
-        self.of.get(region as usize).copied().flatten().map(|(i, _)| i)
+        self.of
+            .get(region as usize)
+            .copied()
+            .flatten()
+            .map(|(i, _)| i)
     }
 
     /// How two regions relate semantically, in `-1.0..=1.0`.
@@ -233,11 +237,7 @@ pub fn apply_semantic_prior(
 ///
 /// The returned ids are sorted, so the same click always produces the same
 /// mask — which is what lets it be a cache key.
-pub fn regions_for_instance(
-    field: &RegionField,
-    mask: &[f32],
-    options: &PriorOptions,
-) -> Vec<u32> {
+pub fn regions_for_instance(field: &RegionField, mask: &[f32], options: &PriorOptions) -> Vec<u32> {
     let mut coverage = vec![0.0f32; field.region_count];
     let mut sizes = vec![0u32; field.region_count];
 
@@ -278,10 +278,26 @@ mod tests {
             labels: vec![0, 0, 2, 2, 1, 1, 3, 3],
             region_count: 4,
             adjacency: vec![
-                Edge { a: 0, b: 1, saddle: 1.0 },
-                Edge { a: 0, b: 2, saddle: 1.0 },
-                Edge { a: 1, b: 3, saddle: 1.0 },
-                Edge { a: 2, b: 3, saddle: 1.0 },
+                Edge {
+                    a: 0,
+                    b: 1,
+                    saddle: 1.0,
+                },
+                Edge {
+                    a: 0,
+                    b: 2,
+                    saddle: 1.0,
+                },
+                Edge {
+                    a: 1,
+                    b: 3,
+                    saddle: 1.0,
+                },
+                Edge {
+                    a: 2,
+                    b: 3,
+                    saddle: 1.0,
+                },
             ],
         }
     }
@@ -361,7 +377,10 @@ mod tests {
     #[test]
     fn zero_strength_is_arm_a_exactly() {
         let f = field();
-        let opts = PriorOptions { strength: 0.0, ..PriorOptions::default() };
+        let opts = PriorOptions {
+            strength: 0.0,
+            ..PriorOptions::default()
+        };
         let m = Membership::compute(&f, &[&left_half()], &opts).unwrap();
         assert_eq!(apply_semantic_prior(&f, &m, &opts).adjacency, f.adjacency);
     }
@@ -394,7 +413,11 @@ mod tests {
         let err = Membership::compute(&f, &[&vec![0.0; 3]], &PriorOptions::default()).unwrap_err();
         assert_eq!(
             err,
-            MembershipError::MaskSize { instance: 0, expected: 8, got: 3 }
+            MembershipError::MaskSize {
+                instance: 0,
+                expected: 8,
+                got: 3
+            }
         );
     }
 
@@ -403,12 +426,8 @@ mod tests {
     fn different_instances_repel() {
         let f = field();
         let right_half = vec![0.0, 0.0, 1.0, 1.0, 0.0, 0.0, 1.0, 1.0];
-        let m = Membership::compute(
-            &f,
-            &[&left_half(), &right_half],
-            &PriorOptions::default(),
-        )
-        .unwrap();
+        let m = Membership::compute(&f, &[&left_half(), &right_half], &PriorOptions::default())
+            .unwrap();
 
         assert_eq!(m.instance_of(0), Some(0));
         assert_eq!(m.instance_of(2), Some(1));