paint bucket back to functionality

lightningbeam-ui/lightningbeam-core/src/actions/paint_bucket.rs

@@ -55,22 +55,28 @@ impl Action for PaintBucketAction {
         // Record for debug test generation (if recording is active)
         dcel.record_paint_point(self.click_point);
 
-        // Hit-test to find which face was clicked
-        let face_id = dcel.find_face_containing_point(self.click_point);
+        // Find the enclosing cycle for the click point
+        let query = dcel.find_face_at_point(self.click_point);
 
         // Dump cumulative test to stderr after every paint click (if recording)
-        // Do this before the early return so failed clicks are captured too.
         if dcel.is_recording() {
-            eprintln!("\n--- DCEL debug test (cumulative, face={:?}) ---", face_id);
+            eprintln!("\n--- DCEL debug test (cumulative, face={:?}) ---", query.face);
             dcel.debug_recorder.as_ref().unwrap().dump_test("test_recorded");
             eprintln!("--- end test ---\n");
         }
 
-        if face_id.0 == 0 {
-            // FaceId(0) is the unbounded exterior face — nothing to fill
+        if query.cycle_he.is_none() {
+            // No edges at all — nothing to fill
             return Err("No face at click point".to_string());
         }
 
+        // If the cycle is in F0 (no face created yet), create one now
+        let face_id = if query.face.0 == 0 {
+            dcel.create_face_at_cycle(query.cycle_he)
+        } else {
+            query.face
+        };
+
         // Store for undo
         self.hit_face = Some(face_id);
         self.old_fill_color = Some(dcel.face(face_id).fill_color.clone());

lightningbeam-ui/lightningbeam-core/src/dcel2/topology.rs

@@ -528,6 +528,19 @@ impl Dcel {
         HalfEdgeId::NONE
     }
 
+    /// Create a face from an existing cycle of half-edges in F0.
+    ///
+    /// Use this when a closed boundary exists but no face was created
+    /// (e.g. paint bucket on a region that hasn't been filled yet).
+    /// The cycle's half-edges are assigned to the new face.
+    /// Returns the new FaceId.
+    pub fn create_face_at_cycle(&mut self, cycle_he: HalfEdgeId) -> FaceId {
+        let face = self.alloc_face();
+        self.faces[face.idx()].outer_half_edge = cycle_he;
+        self.assign_cycle_face(cycle_he, face);
+        face
+    }
+
     /// Re-sort all outgoing half-edges at a vertex by angle and fix the
     /// fan linkage (`twin.next` / `prev`). Call this after operations that
     /// add outgoing half-edges to an existing vertex without maintaining