feat(storage): ext4-only disk via mkfs.ext4 -d; drop FAT16; feature-gated mount (ro on unknown ro_compat); ext4 read spans blocks, delete clears inode, mkdir counts dir; virtio-blk writes; test-qemu e2fsck gate

scripts/test-qemu.sh

@@ -17,7 +17,19 @@ timeout ${QT:-120} qemu-system-riscv64 -machine virt -smp "${SMP}" -bios default
 status=$?
 
 grep -a "smptest:\|spawntest:\|Hello\|SMPTEST" "${LOG}"
-if grep -aq "SMPTEST PASS" "${LOG}"; then
+# What k-os wrote must be ext4 that the real tools accept.
+disk_ok=1
+if command -v e2fsck >/dev/null && command -v debugfs >/dev/null; then
+    if ! e2fsck -fn "${IMAGE}" >"${LOG}.fsck" 2>&1; then
+        echo "test-qemu: e2fsck rejects the disk:"; cat "${LOG}.fsck"; disk_ok=0
+    elif [ "$(debugfs -R 'cat /selftest.txt' "${IMAGE}" 2>/dev/null)" != "written by k-os on ext4" ]; then
+        echo "test-qemu: /selftest.txt is not on the disk"; disk_ok=0
+    else
+        echo "test-qemu: e2fsck clean, file on disk"
+    fi
+    rm -f "${LOG}.fsck"
+fi
+if [ "${disk_ok}" -eq 1 ] && grep -aq "SMPTEST PASS" "${LOG}"; then
     echo "test-qemu: pass (${SMP} harts)"
     rm -f "${LOG}"
     exit 0