hide the cursor the server draws — yours is the accurate one

`-nocursor`. The RFB client asks for Raw and CopyRect and nothing else, so
x11vnc has no cursor pseudo-encoding to send a shape through and composites
the pointer into the framebuffer instead. That is a second cursor in the
picture, a round trip behind the real one, and on a bare X server with no
window manager it is the big black X of the root cursor rather than an arrow.

Verified on the live socket by parking the pointer at 100,100 and counting
what is not stage-teal in a 48x48 patch around it: 960 pixels before, 0 after.

Not fixed by teaching the client the cursor encodings — the answer is not to
draw the remote cursor better, it is not to draw it at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: de3ed4e6-f88a-429c-94e6-a760336ba83b

sidecar/session.ts

@@ -318,7 +318,15 @@ async function startInner(log: (line: string) => void): Promise<SessionStatus> {
       // -solid: the stage is bigger than the game, so the surround is now something people look at. Teal
       // rather than the root's black, which reads as a broken stream rather than a desktop. x11vnc sets it
       // itself on a bare display, so this costs no new host binary.
-      ['x11vnc', '-display', display!, '-unixsock', VNC_SOCKET, '-rfbport', '0', '-rfbportv6', '0', '-noipv6', '-solid', STAGE_COLOUR, '-forever', '-shared', '-nopw', '-noxdamage', '-wait', '5', '-defer', '5'],
+      //
+      // -nocursor: the browser already draws a cursor over the canvas, and it is the accurate one. The
+      // client asks for Raw and CopyRect and nothing else — no cursor pseudo-encoding — so x11vnc has
+      // nowhere to send a cursor SHAPE and composites it into the framebuffer instead. That put a second
+      // pointer in the picture, lagging the real one by a round trip and, on a bare X server with no
+      // window manager, drawn as the big black X of the root cursor. Hiding it server-side is the fix;
+      // adding the pseudo-encoding to the client would be a worse one, since the answer is not to draw
+      // the remote cursor better but not to draw it at all.
+      ['x11vnc', '-display', display!, '-unixsock', VNC_SOCKET, '-rfbport', '0', '-rfbportv6', '0', '-noipv6', '-solid', STAGE_COLOUR, '-nocursor', '-forever', '-shared', '-nopw', '-noxdamage', '-wait', '5', '-defer', '5'],
       { DISPLAY: display! },
       'x11vnc',
     );