fastboot: merge initramfs archives via extract+repack (avoid cat)

The current initramfs merge logic concatenates cpio payloads using `cat`.
Stream concatenation does not merge filesystem structure and can break early
boot path/symlink resolution when firmware and symlinks are split across
multiple archives.

Replace the `cat` approach with an extract-into-one-dir + repack workflow when
firmware_name is provided:
  - extract ramdisk into a staging rootfs
  - extract firmware archive into the same staging tree
  - repack as a single newc cpio.gz (preserving symlinks and hierarchy)

If firmware_name is not provided, the template produces the merged output by
renaming the original ramdisk artifact to merged-initramfs.cpio.gz.

This improves reliability of /lib -> /usr/lib and /lib/firmware resolution
during early boot and avoids firmware load failures.

Signed-off-by: Tharun Kumar Merugu <mtharu@qti.qualcomm.com>

Author: quic-mtharu

templates/boot/fastboot.jinja2

@@ -29,14 +29,19 @@
       docker:
         image: ghcr.io/mwasilew/docker-mkbootimage:master
         steps:
-        - gunzip -c {{ ramdisk_name }} > initramfs-kerneltest-full-image-qcom-armv8a.cpio
         {% if firmware_name %}
-        - gunzip -c {{ firmware_name }} > initramfs-firmware-rb3gen2-image-qcom-armv8a.cpio
-        - cat initramfs-kerneltest-full-image-qcom-armv8a.cpio initramfs-firmware-rb3gen2-image-qcom-armv8a.cpio > merged-initramfs.cpio
+        - rm -rf rootfs
+        - mkdir -p rootfs
+        - cd rootfs
+        - apt-get update -q && DEBIAN_FRONTEND=noninteractive apt-get install -y cpio gzip
+        - gzip -cd ../{{ ramdisk_name }} | cpio -idm --no-absolute-filenames
+        - gzip -cd ../{{ firmware_name }} | cpio -idm --no-absolute-filenames
+        - find . -print0 | cpio --null -H newc -o | gzip -9 > ../merged-initramfs.cpio.gz
+        - cd ..
         {% else %}
-        - cat initramfs-kerneltest-full-image-qcom-armv8a.cpio > merged-initramfs.cpio
+        # No firmware to merge: rename ramdisk as merged output (destructive)
+        - mv {{ ramdisk_name }} merged-initramfs.cpio.gz
         {% endif %}
-        - gzip merged-initramfs.cpio
         - mkbootimg --header_version 2 --kernel Image --dtb {{ dtb_name }} --cmdline "console=ttyMSM0,115200n8 earlycon qcom_geni_serial.con_enabled=1 kernel.sched_pelt_multiplier=4 mem_sleep_default=s2idle mitigations=auto video=efifb:off" --ramdisk merged-initramfs.cpio.gz --output boot.img
     to: downloads