fix(ui): pin outer width to prevent recorder window growth under fractional scaling

electron/recorder-window-sizing.test.ts

@@ -72,3 +72,61 @@ test("recorder fitting clamps content height and ignores invalid requests", () =
   fitRecorderHeight(win, 500);
   assert.deepEqual(win.size, size);
 });
+
+class FractionalScalingWindow implements RecorderWindowSizingTarget {
+  destroyed = false;
+  resizable = false;
+  size: [number, number] = [401, 500];
+  setSizeCalls = 0;
+
+  constructor(private readonly heightRoundingError: number) {}
+
+  isDestroyed(): boolean {
+    return this.destroyed;
+  }
+
+  getContentSize(): [number, number] {
+    const frame: [number, number] = this.resizable ? [16, 39] : [2, 31];
+    return [this.size[0] - frame[0], this.size[1] - frame[1]];
+  }
+
+  getSize(): [number, number] {
+    return [...this.size];
+  }
+
+  isResizable(): boolean {
+    return this.resizable;
+  }
+
+  setResizable(resizable: boolean): void {
+    this.resizable = resizable;
+  }
+
+  setSize(width: number, height: number): void {
+    this.setSizeCalls++;
+    this.size = [width + 2, height + this.heightRoundingError];
+  }
+}
+
+test("recorder fitting prevents width growth across repeated fractional-scale resizing", () => {
+  const win = new FractionalScalingWindow(3);
+
+  fitRecorderHeight(win, 600);
+  const widthAfterFirstFit = win.size[0];
+
+  for (let i = 0; i < 10; i++) {
+    fitRecorderHeight(win, 600);
+  }
+
+  assert.equal(win.setSizeCalls, 11);
+  assert.equal(win.size[0], widthAfterFirstFit);
+});
+
+test("recorder fitting accepts fractional-scale height differences within tolerance", () => {
+  const win = new FractionalScalingWindow(2);
+
+  fitRecorderHeight(win, 600);
+  fitRecorderHeight(win, 600);
+
+  assert.equal(win.setSizeCalls, 1);
+});

electron/recorder-window-sizing.ts

@@ -10,6 +10,9 @@ export interface RecorderWindowSizingTarget {
   setSize(width: number, height: number, animate?: boolean): void;
 }
 
+const pinnedOuterWidths = new WeakMap<RecorderWindowSizingTarget, number>();
+const HEIGHT_TOLERANCE = 2;
+
 /**
  * Fit the recorder to its rendered content while preserving its fixed outer width.
  * Windows changes the non-client frame thickness when resizability is toggled, so
@@ -26,14 +29,20 @@ export function fitRecorderHeight(
     Math.max(RECORDER_MIN_HEIGHT, Math.min(RECORDER_MAX_HEIGHT, contentHeight)),
   );
   const [, currentContentHeight] = win.getContentSize();
-  if (Math.abs(currentContentHeight - targetContentHeight) < 1) return;
+  if (Math.abs(currentContentHeight - targetContentHeight) <= HEIGHT_TOLERANCE) return;
 
   const [outerWidth, outerHeight] = win.getSize();
+  let pinnedWidth = pinnedOuterWidths.get(win);
+  if (pinnedWidth === undefined) {
+    pinnedWidth = outerWidth;
+    pinnedOuterWidths.set(win, pinnedWidth);
+  }
+
   const targetOuterHeight = outerHeight + targetContentHeight - currentContentHeight;
   const wasResizable = win.isResizable();
   if (!wasResizable) win.setResizable(true);
   try {
-    win.setSize(outerWidth, targetOuterHeight);
+    win.setSize(pinnedWidth, targetOuterHeight);
   } finally {
     if (!wasResizable && !win.isDestroyed()) win.setResizable(false);
   }