Fix ARM64 ISO: mkfs.fat PATH wrapper to guarantee EFI FAT headroom

Replace the fragile Python regex patch (which failed to match the actual
awk variable name in mkarchiso) with a mkfs.fat wrapper script placed
earlier in PATH. The wrapper intercepts every -C (create) invocation and
adds +128 MiB (131072 KiB) to the size argument, ensuring the ~50 MB
ARM64 kernel Image + FAT filesystem overhead fits regardless of which
exact size formula the installed mkarchiso version uses.

Also adds a grep of mkarchiso's size lines to stdout so the formula is
visible in build logs for future debugging.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/docker/entrypoint-arm64.sh

@@ -657,9 +657,9 @@ echo "=== /usr/lib/modules/ ==="
 ls /usr/lib/modules/ 2>&1 || echo "(empty)"
 echo "=== end diagnostics ==="
 
-# ALARM aarch64 sometimes installs the kernel as /boot/Image (uncompressed EFI
-# stub) rather than /boot/vmlinuz-linux-aarch64. Archiso's vmlinuz glob and
-# systemd-boot both expect the vmlinuz-* naming — create a symlink when needed.
+# ALARM aarch64 may install the kernel as /boot/Image (uncompressed EFI
+# stub) rather than /boot/vmlinuz-linux-aarch64. Archiso's vmlinuz-* glob
+# and systemd-boot both expect the vmlinuz-* naming — create a symlink.
 if [[ ! -f /boot/vmlinuz-linux-aarch64 ]]; then
     if [[ -f /boot/Image ]]; then
         ln -sf Image /boot/vmlinuz-linux-aarch64
@@ -729,28 +729,29 @@ echo "OrionOS ARM64 customization complete."
 CUSTOMIZE
 chmod 755 "$PROFILE/airootfs/root/customize_airootfs.sh"
 
-# ── 13. Patch mkarchiso EFI FAT image size ───────────────────────────
-# The ARM64 kernel (Image) is ~50 MB. mkarchiso's default size formula is
-# int(total_bytes/1024/1024)+2 MiB, which leaves no room for FAT overhead
-# and causes "Disk full". Bump the buffer to +128 MiB.
-python3 - <<'PYEOF'
-import re, sys
-with open('/usr/bin/mkarchiso') as f:
-    txt = f.read()
-orig = txt
-# Match: int($1 / 1024 / 1024) + N  (with any spacing or small N)
-txt = re.sub(
-    r'int\(\$1\s*/\s*1024\s*/\s*1024\s*\)\s*\+\s*\d+',
-    r'int($1 / 1024 / 1024) + 128',
-    txt
-)
-if txt == orig:
-    print('mkarchiso: FAT size pattern not found — build may fail with Disk full', file=sys.stderr)
-else:
-    with open('/usr/bin/mkarchiso', 'w') as f:
-        f.write(txt)
-    print('mkarchiso: patched EFI FAT size buffer to +128 MiB')
-PYEOF
+# ── 13. Fix EFI FAT image size for the large ARM64 kernel ────────────
+# mkarchiso calculates EFI FAT image size as roughly (kernel+initramfs MiB)+N
+# but the ARM64 kernel Image is ~50 MB and FAT filesystem overhead pushes
+# the total over the calculated limit → "Disk full".
+#
+# Strategy: put a mkfs.fat wrapper earlier in PATH that transparently adds
+# +128 MiB to every -C (create) call. This works regardless of which exact
+# formula the installed mkarchiso version uses.
+cat > /usr/local/bin/mkfs.fat <<'MKFAT'
+#!/usr/bin/bash
+args=("$@")
+# When creating (-C) the EFI FAT image, add 128 MiB to the requested size
+if [[ " ${args[*]} " == *" -C "* ]] && [[ "${args[-1]}" =~ ^[0-9]+$ ]]; then
+    args[-1]=$(( ${args[-1]} + 131072 ))   # +128 MiB in KiB blocks
+fi
+exec /usr/bin/mkfs.fat "${args[@]}"
+MKFAT
+chmod +x /usr/local/bin/mkfs.fat
+export PATH="/usr/local/bin:$PATH"
+echo ">>> mkfs.fat wrapper active — EFI FAT creation gets +128 MiB headroom"
+echo ">>> mkarchiso EFI size lines (for reference):"
+grep -n "1024.*1024\|fat.*size\|efi.*size\|img_size" /usr/bin/mkarchiso 2>/dev/null \
+    | grep -iv "^[0-9]*:#\|comment" | head -8 || true
 
 # ── 14. Build the ISO ─────────────────────────────────────────────────
 echo ">>> Building ARM64 ISO (this takes 5-15 minutes)..."