fix(editor): snap smoothed cursor to click positions during spring simulation

Spring physics smoothing caused the cursor to lag behind click highlight
positions, especially at slower speeds. Add output correction that blends
toward upcoming click positions using smoothstep interpolation, and snaps
the spring state at click time to ensure alignment.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jkuri

Reframed/Editor/CursorSmoothing.swift

@@ -44,18 +44,31 @@ enum CursorMovementSpeed: String, Codable, Sendable, CaseIterable, Identifiable
     case .rapid: 0.6
     }
   }
+
+  var convergenceDuration: Double {
+    switch self {
+    case .slow: 0.3
+    case .medium: 0.2
+    case .fast: 0.15
+    case .rapid: 0.1
+    }
+  }
 }
 
 enum CursorSmoothing {
   static func smooth(
     samples: [CursorSample],
-    speed: CursorMovementSpeed
+    speed: CursorMovementSpeed,
+    clicks: [CursorClickEvent] = []
   ) -> [CursorSample] {
     guard samples.count >= 2 else { return samples }
 
     let tension = speed.tension
     let friction = speed.friction
     let mass = speed.mass
+    let convergence = speed.convergenceDuration
+    let sortedClicks = clicks.sorted { $0.t < $1.t }
+    var clickIdx = 0
 
     var result: [CursorSample] = []
     result.reserveCapacity(samples.count)
@@ -77,6 +90,9 @@ enum CursorSmoothing {
         velX = 0
         velY = 0
         result.append(CursorSample(t: target.t, x: posX, y: posY, p: target.p))
+        while clickIdx < sortedClicks.count && sortedClicks[clickIdx].t <= target.t {
+          clickIdx += 1
+        }
         continue
       }
 
@@ -92,7 +108,38 @@ enum CursorSmoothing {
         posY += velY * stepDt
       }
 
-      result.append(CursorSample(t: target.t, x: posX, y: posY, p: target.p))
+      while clickIdx < sortedClicks.count && sortedClicks[clickIdx].t <= prev.t {
+        clickIdx += 1
+      }
+
+      if clickIdx < sortedClicks.count {
+        let click = sortedClicks[clickIdx]
+        if click.t > prev.t && click.t <= target.t {
+          posX = click.x
+          posY = click.y
+          velX = 0
+          velY = 0
+          result.append(CursorSample(t: target.t, x: posX, y: posY, p: target.p))
+          clickIdx += 1
+          continue
+        }
+      }
+
+      var outX = posX
+      var outY = posY
+
+      if clickIdx < sortedClicks.count {
+        let click = sortedClicks[clickIdx]
+        let timeToClick = click.t - target.t
+        if timeToClick > 0 && timeToClick <= convergence {
+          let raw = 1.0 - timeToClick / convergence
+          let blend = raw * raw * (3.0 - 2.0 * raw)
+          outX = posX + (click.x - posX) * blend
+          outY = posY + (click.y - posY) * blend
+        }
+      }
+
+      result.append(CursorSample(t: target.t, x: outX, y: outY, p: target.p))
     }
 
     return result

Reframed/Editor/EditorState.swift

@@ -1369,7 +1369,8 @@ final class EditorState {
     }
     let smoothedSamples = CursorSmoothing.smooth(
       samples: provider.metadata.samples,
-      speed: cursorMovementSpeed
+      speed: cursorMovementSpeed,
+      clicks: provider.metadata.clicks
     )
     var smoothedMetadata = provider.metadata
     smoothedMetadata.samples = smoothedSamples