fix(session/gamelease): a launcher handing off is not the game exiting

On glass (.41), launching any Steam title over the compat plane ended the
session ~7 s later, before the game had started:

  launched app  command=steam steam://rungameid/2379780  pid=12699
  watching the launched game  kind="child"
  the launched game is running  kind="child"  procs=0      <- 3 ms in, zero game procs
  the launched game exited  ->  session ended

Linux launches are `Child` leases: the host spawns the launcher itself. The
watcher counts "my child is alive" as the game running, so the lease left the
waiting phase on its FIRST poll — and the shim reclassification lives in that
phase, so it never got to run. When `steam` handed off and exited, that read as
the game exiting.

The design always called for the shim window ("never fires B from a shim exit")
and the code implements it; the lease had simply moved past where it applies. So
when the store gave us signals to recognize the real game by, a bare live child
no longer counts as the game until that window has passed. With no signals the
child is all we have and still counts immediately — custom commands are
unchanged.

Windows could not reproduce this: it holds no child, so its leases are always
`Matched`, and the whole .173 pass was structurally blind to it. Both planes on
Linux were affected — which is most of the audience for this feature.

Also fixes the live-process fixture, which was CI-red for an unrelated reason:
it copied `/bin/sleep` to a file named `game`, and modern coreutils (uutils on
Ubuntu 25.10+, busybox elsewhere) is a MULTI-CALL binary dispatching on argv[0]
— under any other name it exits instantly, leaving nothing in /proc and looking
exactly like a broken matcher. Verified by A/B: the same test fails identically
on a tree predating these changes.

.25 (Ubuntu 26.04): 305 passed, 0 failed.

crates/punktfunk-host/src/procscan/linux.rs

@@ -542,8 +542,14 @@ mod tests {
         // it from there. (A wrapper script that `exec`s something outside the directory would leave no
         // trace of the directory in either the image path or the command line — worth knowing, and the
         // reason a copied binary is the honest fixture here.)
+        //
+        // It has to keep the name `sleep`. Modern coreutils (uutils on Ubuntu 25.10+, busybox
+        // elsewhere) is a MULTI-CALL binary that dispatches on `argv[0]`: copied to any other name it
+        // prints "unknown program" and exits instantly, leaving nothing in `/proc` to find — which
+        // looks exactly like the matcher being broken. That cost a CI red, green on a distro with a
+        // standalone `sleep` and failing on one without.
         let td = tempfile::tempdir().expect("tempdir");
-        let game = td.path().join("game");
+        let game = td.path().join("sleep");
         std::fs::copy("/bin/sleep", &game).expect("copy a stand-in game binary");
         let s = Scanner::system();
         let before = s.now_stamp().expect("real /proc/uptime is readable");