fix: share title bar bounds between load and resize

The initial bounds in load() spanned the full content width with no inset,
while _resizeViews() insets by 1px on non-macOS, so the title bar gapped by a
pixel on the first paint until the first resize corrected it. Compute the
bounds once in _titleBarBounds() and use it from both so the first paint
matches every later resize.

Note: AI-assisted (Claude Code). Manually verified: tsc and eslint clean, added a unit test for the macOS and non-macOS rects and confirmed it fails when the inset is removed.

Author: notluquis

src/main/sessionwindow/sessionwindow.ts

@@ -170,13 +170,7 @@ export class SessionWindow implements IDisposable {
   load() {
     const titleBarView = new TitleBarView({ isDarkTheme: this._isDarkTheme });
     this._window.contentView.addChildView(titleBarView.view);
-    const { width: contentWidth } = this._window.getContentBounds();
-    titleBarView.view.setBounds({
-      x: 0,
-      y: 0,
-      width: contentWidth,
-      height: titleBarHeight
-    });
+    titleBarView.view.setBounds(this._titleBarBounds());
 
     this._window.on('focus', () => {
       titleBarView.activate();
@@ -1218,16 +1212,23 @@ export class SessionWindow implements IDisposable {
     }, 300);
   }
 
-  private _resizeViews() {
-    const { width, height } = this._window.getContentBounds();
-    // add padding to allow resizing around title bar
+  // Title bar bounds, shared by load() and _resizeViews() so the first paint
+  // matches every later resize. Non-macOS insets by 1px so the frame stays
+  // grabbable for resizing around the title bar.
+  private _titleBarBounds(): Electron.Rectangle {
+    const { width } = this._window.getContentBounds();
     const padding = process.platform === 'darwin' ? 0 : 1;
-    this._titleBarView.view.setBounds({
+    return {
       x: padding,
       y: padding,
       width: width - 2 * padding,
       height: titleBarHeight - padding
-    });
+    };
+  }
+
+  private _resizeViews() {
+    const { width, height } = this._window.getContentBounds();
+    this._titleBarView.view.setBounds(this._titleBarBounds());
     const contentRect: Electron.Rectangle = {
       x: 0,
       y: titleBarHeight,

test/unit/sessionwindow-titlebar-bounds.test.ts

@@ -0,0 +1,40 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { SessionWindow } from '../../src/main/sessionwindow/sessionwindow';
+
+// _titleBarBounds is the single source of truth shared by load() and
+// _resizeViews(); if the two ever diverge again the first paint gaps by a pixel
+// on non-macOS. Drive it directly without the heavy constructor.
+const realPlatform = process.platform;
+function setPlatform(p: string): void {
+  Object.defineProperty(process, 'platform', { value: p, configurable: true });
+}
+
+function windowWith(width: number): any {
+  const win = Object.create(SessionWindow.prototype);
+  win._window = { getContentBounds: () => ({ width, height: 600 }) };
+  return win;
+}
+
+describe('SessionWindow._titleBarBounds', () => {
+  afterEach(() => setPlatform(realPlatform));
+
+  it('spans the full content width with no inset on macOS', () => {
+    setPlatform('darwin');
+    expect(windowWith(800)._titleBarBounds()).toEqual({
+      x: 0,
+      y: 0,
+      width: 800,
+      height: 29
+    });
+  });
+
+  it('insets by one pixel on non-macOS so the frame stays grabbable', () => {
+    setPlatform('linux');
+    expect(windowWith(800)._titleBarBounds()).toEqual({
+      x: 1,
+      y: 1,
+      width: 798,
+      height: 28
+    });
+  });
+});