feat(boot): gatekeeper gates boot (init→UI→gatekeeper→data); keystore disk + virtio-rng discovery; terminal READ_SECRET; storage SET_KEY; PageCount ≤8192, alloc cap gone; device window 0x01D0_0000; test-qemu types passcode over 2 boots

crates/apps/spawntest/src/main.rs

@@ -57,6 +57,8 @@ fn run_hello(fs: &mut Storage, died: CapSlot, grant: Option<CapSlot>) -> Result<
 
 /// A file written through storage, which the host then checks with e2fsck.
 fn write_a_file(fs: &mut Storage) -> Result<(), &'static str> {
+    // Left by an earlier boot of the same disk.
+    let _ = fs.delete(b"selftest.txt");
     let h = fs.create(b"selftest.txt").map_err(|_| "cannot create a file")?;
     if fs.write(h, NOTE) != Ok(NOTE.len()) {
         return Err("short write");