Restore slim terminal scrollbar (xterm width: 7) (#5051)

Co-authored-by: Orca <help@stably.ai>

src/renderer/src/lib/pane-manager/pane-lifecycle.test.ts

@@ -76,8 +76,11 @@ describe('buildDefaultTerminalOptions', () => {
     expect(buildDefaultTerminalOptions().cursorInactiveStyle).toBe('outline')
   })
 
-  it('does not reserve a classic scrollbar gutter when fitting terminal columns', () => {
-    expect(buildDefaultTerminalOptions().scrollbar?.width).toBe(0)
+  it('shows the slim xterm scrollbar in its reserved gutter', () => {
+    // Why: 7px gutter is an accepted ~1-column cost (VS Code reserves 14);
+    // the v1.4.51 table corruption that once forced width 0 was the ZWJ
+    // width bug, fixed separately by the Orca unicode provider.
+    expect(buildDefaultTerminalOptions().scrollbar?.width).toBe(7)
   })
 
   it('only uses inactive outline for block cursors', () => {

src/renderer/src/lib/pane-manager/pane-terminal-options.ts

@@ -32,9 +32,14 @@ export function buildDefaultTerminalOptions(): ITerminalOptions {
     macOptionClickForcesSelection: true,
     drawBoldTextInBrightColors: true,
     scrollbar: {
-      // Why: xterm's DOM scrollbar overlays the terminal in Electron; reserving
-      // gutter width in FitAddon underfits wide table/TUI output by a column.
-      width: 0
+      // Why: slim VS Code-style scrollbar (VS Code uses 14). FitAddon reserves
+      // this as a gutter, costing ~1 column per pane — accepted tradeoff so the
+      // scrollbar never covers content (evidence in PR #5051). The v1.4.51
+      // table corruption #4877 fixed by zeroing this was actually the ZWJ
+      // width bug; it stays fixed by pane-terminal-unicode-provider.ts. Width
+      // also enables the overview ruler, whose border is hidden in
+      // composeActiveTerminalTheme.
+      width: 7
     },
     // Why: advertise kitty keyboard protocol support so CLIs that probe
     // (CSI ? u) know Orca accepts enhanced key reporting. Orca still writes