diff --git a/src/servers/sidecar/vnc/vnc-manager.ts b/src/servers/sidecar/vnc/vnc-manager.ts
index 9c04a68f..9eb9cdaf 100644
--- a/src/servers/sidecar/vnc/vnc-manager.ts
+++ b/src/servers/sidecar/vnc/vnc-manager.ts
@@ -231,7 +231,15 @@ export async function startSession(params: VncStartParams): Promise<{ port: numb
       '-shared',
       ...clip,
       ...scale,
-      '-noxdamage',
+      // No -noxdamage. It was set when this was written, with no recorded reason, and it is expensive:
+      // without the DAMAGE extension x11vnc cannot be told which rectangles changed, so it polls the
+      // WHOLE framebuffer continuously to find out. That makes cost scale with screen area rather than
+      // with what actually moved — on a 4K mirror it is the single biggest source of latency, and it is
+      // why a smaller machine felt instant by comparison. This X server reports DAMAGE, MIT-SHM and
+      // XFIXES, so the optimisation is genuinely available.
+      //
+      // If stale patches ever appear on screen (some drivers under-report damage), putting -noxdamage
+      // back is the fix — at the cost of the polling above.
       '-quiet',
     ],
     stdout: 'ignore',