fix: extract original ISO boot stanza programmatically (no hardcoded paths)

Reviewer found `-e images/efiboot.img` was wrong — Fedora livecd-creator
places efiboot.img in isolinux/ not images/. Plus missing
--mbr-force-bootable + -partition_* flags would produce hybrid MBR/GPT
mismatch refused by some BIOS firmwares.

Fix: extract original ISO's exact boot stanza via
`xorriso -report_el_torito as_mkisofs` and replay it via eval.
Guarantees exact match, immune to upstream Fedora layout changes.

.github/workflows/build-iso.yml

@@ -127,8 +127,15 @@ jobs:
             [ -n "$ISO_FILE" ] || { echo "[ERR] no ISO produced by livecd-creator"; exit 1; }
             echo "[INFO] grafting /veilor/ onto $ISO_FILE"
 
-            # Inspect original boot stanza so the rebuild matches livecd-creator's layout.
+            # Extract original ISO's exact boot stanza so the rebuild matches
+            # livecd-creator's layout byte-for-byte. This is immune to upstream
+            # Fedora layout changes (e.g. images/ vs isolinux/ for efiboot.img,
+            # partition geometry flags, hybrid MBR/GPT options).
             xorriso -indev "$ISO_FILE" -report_el_torito as_mkisofs 2>&1 | tee /tmp/iso-boot.txt || true
+            ORIG_FLAGS=$(xorriso -indev "$ISO_FILE" -report_el_torito as_mkisofs 2>/dev/null | \
+                grep -v '^xorriso :' | grep -E '^-' | tr '\n' ' ')
+            [ -n "$ORIG_FLAGS" ] || { echo "[ERR] could not extract boot stanza from $ISO_FILE"; exit 1; }
+            echo "[INFO] re-pack flags from original ISO: $ORIG_FLAGS"
 
             mkdir -p /tmp/iso-mod
             xorriso -osirrox on -indev "$ISO_FILE" -extract / /tmp/iso-mod
@@ -136,15 +143,11 @@ jobs:
             mkdir -p /tmp/iso-mod/veilor
             cp -a /work/overlay /work/scripts /work/assets /tmp/iso-mod/veilor/
 
-            xorriso -as mkisofs \
+            # Replay the exact stanza captured above. eval is needed because
+            # ORIG_FLAGS contains multiple flag/value pairs that must word-split.
+            eval xorriso -as mkisofs \
               -volid "veilor-os-43" \
-              -isohybrid-mbr /usr/share/syslinux/isohdpfx.bin \
+              $ORIG_FLAGS \
-              -eltorito-boot isolinux/isolinux.bin \
-              -eltorito-catalog isolinux/boot.cat \
-              -no-emul-boot -boot-load-size 4 -boot-info-table \
-              -eltorito-alt-boot \
-              -e images/efiboot.img -no-emul-boot \
-              -isohybrid-gpt-basdat \
               -o "${ISO_FILE}.tmp" /tmp/iso-mod
             mv "${ISO_FILE}.tmp" "$ISO_FILE"
             rm -rf /tmp/iso-mod