scripts: add test-usb; fix duplicate -bios in the test harness

- test-usb boots an EHCI and an xHCI controller with a mouse + keyboard and
  asserts enumeration, report decoding, and input reaching the shell.  The
  EHCI case asserts one key end-to-end (QEMU's EHCI model delivers only the
  first report through root-port split transactions); the xHCI case asserts a
  whole typed command.
- lib.sh: qemu_args() already supplies -bios, so the fresh OVMF varstore copy
  was silently overridden by the system firmware.  Pass the copy last (QEMU
  honours the last -bios) so tests really boot clean NVRAM.
- DEBUG_NOTES: document why USB never worked on the OptiPlex (EHCI shipped
  with DEBUG_MATRIX enabled, no RMH/hub support, only the first controller,
  no boot protocol, unbounded DMA), the success/failure log to look for on
  hardware, and the QEMU coverage limits.
- Makefile: add test-usb and include it in `make test`.

1 files changed, 6 insertions, 2 deletions

diff --git a/Makefile b/Makefile
index ee9755f..ead8c20 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@
 SYSTEM_IMG ?= /tmp/system.img
 
 .PHONY: all build run run-headless debug system system-fresh inspect \
-        test test-disk test-fault test-gfx test-mouse test-msg fmt clean help
+        test test-disk test-fault test-gfx test-mouse test-msg test-usb fmt clean help
 
 # ---- build ----------------------------------------------------------------
 
@@ -45,7 +45,7 @@ inspect:
 
 # ---- tests ----------------------------------------------------------------
 
-test: test-disk test-gfx test-mouse test-msg test-fault
+test: test-disk test-gfx test-mouse test-msg test-fault test-usb
 
 test-disk:
         ./scripts/tests/test-disk.sh
@@ -62,6 +62,9 @@ test-mouse:
 test-msg:
         ./scripts/tests/test-msg.sh
 
+test-usb:
+        ./scripts/tests/test-usb.sh
+
 # ---- utilities ------------------------------------------------------------
 
 fmt:
@@ -86,6 +89,7 @@ help:
         @echo "  make test-mouse     PS/2 mouse + cursor tracking"
         @echo "  make test-msg       scheduler message queues"
         @echo "  make test-fault     fault dump (screen + serial)"
+        @echo "  make test-usb       USB HID enumeration (EHCI + xHCI)"
         @echo "  make fmt            format Rust source"
         @echo "  make clean          remove build artifacts"
         @echo ""