components: ReorderableColumn resists dragging past the ends

components/src/main/kotlin/de/jeanlucmakiola/floret/components/ReorderableColumn.kt

@@ -84,6 +84,8 @@ fun <T> ReorderableColumn(
     // release settle — re-based onto the row's new slot once the order commits
     // (see onDragEnd), then eased down to zero.
     var dragOffset by remember { mutableFloatStateOf(0f) }
+    // The finger's own travel; [dragOffset] is this held to the list's ends.
+    var rawOffset by remember { mutableFloatStateOf(0f) }
     // The running release/cancel settle, cancelled if a new drag pre-empts it.
     // Purely visual — the order commit (see onDragEnd) never depends on it.
     var settleJob by remember { mutableStateOf<Job?>(null) }
@@ -131,10 +133,13 @@ fun <T> ReorderableColumn(
                         settleJob?.cancel()
                         draggedKey = key
                         dragOffset = 0f
+                        rawOffset = 0f
                     },
                     onDrag = { change, amount ->
                         change.consume()
-                        dragOffset += amount.y
+                        rawOffset += amount.y
+                        val from = order.indexOfFirst { keyOf(it) == key }
+                        dragOffset = rubberBand(rawOffset, -from * pitchPx, (order.lastIndex - from) * pitchPx, pitchPx * 0.4f)
                     },
                     onDragEnd = {
                         val from = order.indexOfFirst { keyOf(it) == key }
@@ -206,3 +211,16 @@ private class InsetShape(private val base: Shape, private val inset: Dp) : Shape
         }
     }
 }
+
+/**
+ * [value] as is between [min] and [max]; past either end it keeps following with
+ * growing resistance and never gets further than [stretch] beyond it.
+ */
+private fun rubberBand(value: Float, min: Float, max: Float, stretch: Float): Float {
+    fun resist(over: Float) = stretch * (1f - 1f / (over / stretch + 1f))
+    return when {
+        value > max -> max + resist(value - max)
+        value < min -> min - resist(min - value)
+        else -> value
+    }
+}