don't over-constraint layout while resizing

adapting the approach taken in the prototype

src/resizer/distributors/roomsublist2.js

@@ -41,6 +41,14 @@ export class Layout {
         this._sectionHeights = Object.assign({}, initialSizes);
         // in-progress heights, while dragging. Committed on mouse-up.
         this._heights = [];
+        // use while manually resizing to cancel
+        // the resize for a given mouse position
+        // when the previous resize made the layout
+        // constrained
+        this._clampedOffset = 0;
+        // used while manually resizing, to clear
+        // _clampedOffset when the direction of resizing changes
+        this._lastOffset = 0;
     }
 
     setAvailableHeight(newSize) {
@@ -268,6 +276,22 @@ export class Layout {
             this._sectionHeights[section.id] = this._heights[i];
         });
     }
+
+    _setUncommittedSectionHeight(sectionIndex, offset) {
+        if (Math.sign(offset) != Math.sign(this._lastOffset)) {
+            this._clampedOffset = undefined;
+        }
+        if (this._clampedOffset !== undefined) {
+            if (offset < 0 && offset < this._clampedOffset) {
+                return;
+            }
+            if (offset > 0 && offset > this._clampedOffset) {
+                return;
+            }
+        }
+        this._clampedOffset = this._relayout(sectionIndex, offset);
+        this._lastOffset = offset;
+    }
 }
 
 class Handle {
@@ -278,7 +302,10 @@ class Handle {
     }
 
     setHeight(height) {
-        this._layout._relayout(this._sectionIndex, height - this._initialHeight);
+        this._layout._setUncommittedSectionHeight(
+            this._sectionIndex,
+            height - this._initialHeight,
+        );
         return this;
     }