os/mini: ship the xHCI capture on the medium, so engine#823's plug test has an instrument

os/mini/mkimage.sh

@@ -501,6 +501,11 @@ cp /etc/mke2fs.conf "$root/etc/mke2fs.conf"
 # to the stick instead of booting the disk.
 copy_elf /usr/bin/efibootmgr
 cp "$here/release-check.sh" "$root/bin/1bit-release-check"; chmod +x "$root/bin/1bit-release-check"
+# engine#823: the plug test's instrument has to be ON the medium. The capture answers "did a device appear on
+# this port" from the booted system, which is the only place a plug can be observed - a tool that lives only in
+# the source tree cannot be run by the person holding the stick, so the issue would stay open for want of a
+# script rather than for want of hardware.
+install -m 0755 "$src/tools/xhci_boot_capture.sh" "$root/bin/1bit-xhci-capture"
 install -m 0755 "$here/board.sh" "$root/usr/sbin/1bit-board"
 mkdir -p "$root/etc/1bit"
 install -m 0644 "$here/power.conf.example" "$root/etc/1bit/power"

os/mini/release-check.sh

@@ -902,6 +902,14 @@ payload_home_layout_verdict() {   # <links at a FILE or at NOTHING> <links at a
     fi
 }
 
+xhci_capture_verdict() {   # <1 when /bin/1bit-xhci-capture is present and executable, 0 when not>
+    case "${1:-}" in
+        1) printf 'PASS /bin/1bit-xhci-capture is installed and executable: a boot can capture the xHCI state for engine#823, which is the only place a plug can be observed' ;;
+        0) printf 'FAIL /bin/1bit-xhci-capture is not installed: engine#823 asks whether a rear USB-A or Type-C port sees a device, and nothing on this medium can read that' ;;
+        *) printf 'FAIL whether the xHCI capture is installed could not be read (%s)' "${1:-empty}" ;;
+    esac
+}
+
 # --self-test: assert the lemonade verdict on the cases that matter (tests/release_check_row.sh runs
 # this in CI). The unprepared-stick case is the one that used to false-PASS: 200 with the key, an empty
 # body and no status without it.
@@ -953,6 +961,9 @@ if [ "${1:-}" = --self-test ]; then
     ln -s /home/nonexistent-xyz "$_hl_st/opt/home"                 # a home directory target: named, not failed
     check "bin/leak|/home/nonexistent-xyz/wt/build/1bit|dangling" "$(payload_home_layout_bad "$_hl_st" | grep '^bin/leak|')"
     rm -rf "$_hl_st"
+    check PASS "$(xhci_capture_verdict 1)"
+    check FAIL "$(xhci_capture_verdict 0)"
+    check FAIL "$(xhci_capture_verdict '')"
     check PASS "$(payload_runpath_verdict 0)"
     check FAIL "$(payload_runpath_verdict 3 '/opt/1bit-package/1bit/1bit runs /home/x/wt/release-rc/work/build')"
     check FAIL "$(payload_runpath_verdict 1)"
@@ -2362,6 +2373,17 @@ else
 fi
 
 
+# engine#823: the instrument the plug test needs must be on the medium (see os/mini/mkimage.sh).
+if [ -x /bin/1bit-xhci-capture ]; then
+    XC=$(xhci_capture_verdict 1)
+else
+    XC=$(xhci_capture_verdict 0)
+fi
+case "$XC" in
+    PASS*) pass xhci-capture "${XC#PASS }" ;;
+    *)     fail xhci-capture "${XC#FAIL }" ;;
+esac
+
 # ── the NPU's locked memory in force (the driver asks for unlimited; this fleet's own 99- file can override ours) ──
 MEMLOCK_PID=${MEMLOCK_PID:-}
 MEMLOCK_NAME=${MEMLOCK_NAME:-}