Make the secondary-cursor sprite opt-in and expire stale entries

Live report: a second cursor appeared uninvited and unusably (frozen,
uncontrollable) on screen. Multi-cursor Phase 1 rendered one sprite per
physical libinput pointer device that had ever reported a position, with
no way to turn it off and no expiry - so a phantom device (a real mouse's
side-button/scroll cluster enumerating as its own HID path is a common
case) that reports once and never moves again left a frozen ghost sprite
with nothing to control or dismiss it.

Adds general.multi_cursor (default false, live-settable via
`srd set multi_cursor <bool>`) and keys secondary_cursors to
(Point, Instant) so both the recording side (udev/session.rs) and the
render side (udev/render.rs) drop any entry older than
SECONDARY_CURSOR_TIMEOUT (1.5s). The "agent controls a window without
interrupting the user" use case this report also raised was never gated
on this flag - that's Multi-cursor Phase 2's pinned virtual-pointer
delivery, which never shows a visible cursor at all.

1 files changed, 10 insertions, 2 deletions

diff --git a/crates/ctl/src/main.rs b/crates/ctl/src/main.rs
index d714405..3cf3bfd 100644
--- a/crates/ctl/src/main.rs
+++ b/crates/ctl/src/main.rs
@@ -178,14 +178,14 @@ fn build_request(args: &[String]) -> Result<String, String> {
         // as booleans at all, not a string it then has to reject.
         Some("set") => {
             let key = args.get(1).ok_or(
-                "set needs a key (border_width/border_color/corner_radius/gap_inner/gap_outer/shadows/rounded_corners/animations/night_light/reading_mode/phone_mode/decoration_mode)",
+                "set needs a key (border_width/border_color/corner_radius/gap_inner/gap_outer/shadows/rounded_corners/animations/night_light/reading_mode/phone_mode/multi_cursor/decoration_mode)",
             )?;
             let raw = args.get(2).ok_or("set needs a value")?;
             let value = match key.as_str() {
                 "border_width" | "corner_radius" | "gap_inner" | "gap_outer" => {
                     raw.parse::<u64>().map_err(|_| format!("{key} needs a numeric value"))?.to_string()
                 }
-                "shadows" | "rounded_corners" | "animations" | "night_light" | "reading_mode" | "phone_mode" => match raw.as_str() {
+                "shadows" | "rounded_corners" | "animations" | "night_light" | "reading_mode" | "phone_mode" | "multi_cursor" => match raw.as_str() {
                     "true" | "false" => raw.clone(),
                     _ => return Err(format!("{key} needs 'true' or 'false'")),
                 },
@@ -401,6 +401,7 @@ fn print_usage() {
     eprintln!("  srd set night_light <true|false>");
     eprintln!("  srd set reading_mode <true|false>");
     eprintln!("  srd set phone_mode <true|false>");
+    eprintln!("  srd set multi_cursor <true|false>");
     eprintln!("  srd set decoration_mode <server|client>");
 }
 
@@ -479,6 +480,13 @@ mod tests {
     }
 
     #[test]
+    fn set_multi_cursor_accepts_only_true_or_false() {
+        assert_eq!(build_request(&args(&["set", "multi_cursor", "true"])).unwrap(), r#"{"cmd":"set","key":"multi_cursor","value":true}"#);
+        assert_eq!(build_request(&args(&["set", "multi_cursor", "false"])).unwrap(), r#"{"cmd":"set","key":"multi_cursor","value":false}"#);
+        assert!(build_request(&args(&["set", "multi_cursor", "maybe"])).is_err());
+    }
+
+    #[test]
     fn set_phone_mode_accepts_only_true_or_false() {
         assert_eq!(build_request(&args(&["set", "phone_mode", "true"])).unwrap(), r#"{"cmd":"set","key":"phone_mode","value":true}"#);
         assert_eq!(build_request(&args(&["set", "phone_mode", "false"])).unwrap(), r#"{"cmd":"set","key":"phone_mode","value":false}"#);