fix: make RPi partition 1 self-sufficient boot fallback

The autoboot.txt A/B redirect requires newer RPi EEPROM firmware.
On older EEPROMs, autoboot.txt is silently ignored and the firmware
tries to boot from partition 1 directly — failing with a rainbow
screen because partition 1 had no kernel or initramfs.

Changes:
- Increase partition 1 from 32 MB to 384 MB
- Populate partition 1 with full boot files (kernel, initramfs,
  config.txt with kernel= directive, DTBs, overlays)
- Keep autoboot.txt for A/B redirect on supported EEPROMs
- When autoboot.txt works: boots from partition 2 (A/B scheme)
- When autoboot.txt is unsupported: boots from partition 1 (fallback)

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

build/scripts/create-rpi-image.sh

@@ -2,14 +2,14 @@
 # create-rpi-image.sh — Create a raw disk image for Raspberry Pi SD card
 #
 # Partition layout (MBR):
-#   Part 1: Boot Control  (32 MB, FAT32, label KSOLOCTL) — firmware + autoboot.txt
+#   Part 1: Boot/Control  (384 MB, FAT32, label KSOLOCTL) — firmware + kernel + initramfs + autoboot.txt
 #   Part 2: Boot A        (256 MB, FAT32, label KSOLOA)  — kernel + DTBs + initramfs
 #   Part 3: Boot B        (256 MB, FAT32, label KSOLOB)  — same as Boot A (initially identical)
 #   Part 4: Data          (remaining of 2GB, ext4, label KSOLODATA)
 #
-# The RPi EEPROM loads start4.elf from partition 1 (KSOLOCTL).
-# autoboot.txt on partition 1 redirects boot_partition to 2 (Boot A) or 3 (Boot B).
-# The firmware then loads config.txt, kernel, and initramfs from the selected partition.
+# The RPi EEPROM loads start4.elf from partition 1.
+# If autoboot.txt is supported (newer EEPROM), firmware redirects to partition 2/3 for A/B boot.
+# If autoboot.txt is NOT supported (older EEPROM), partition 1 has full boot files as fallback.
 #
 # MBR is required — GPT + autoboot.txt is not reliably supported on Pi 4.
 #
@@ -69,15 +69,16 @@ dd if=/dev/zero of="$IMG_OUTPUT" bs=1M count=0 seek="$IMG_SIZE_MB" 2>/dev/null
 # --- Partition table (MBR) ---
 # MBR is required for reliable RPi boot with autoboot.txt.
 # GPT + autoboot.txt fails on many Pi 4 EEPROM versions.
-# Part 1: Boot Control  32 MB FAT32 (firmware + autoboot.txt)
+# Part 1: Boot/Control 384 MB FAT32 (firmware + kernel + initramfs + autoboot.txt)
 # Part 2: Boot A       256 MB FAT32 (kernel + initramfs + DTBs)
 # Part 3: Boot B       256 MB FAT32 (kernel + initramfs + DTBs)
 # Part 4: Data         remaining ext4
 sfdisk "$IMG_OUTPUT" << EOF
 label: dos
 
-# Boot Control partition: 32 MB, FAT32 (type 0c = W95 FAT32 LBA)
-start=2048, size=65536, type=c, bootable
+# Boot/Control partition: 384 MB, FAT32 (type 0c = W95 FAT32 LBA)
+# Contains firmware + autoboot.txt for A/B redirect, PLUS full boot files as fallback
+start=2048, size=786432, type=c, bootable
 # Boot A partition: 256 MB, FAT32
 size=524288, type=c
 # Boot B partition: 256 MB, FAT32
@@ -149,46 +150,6 @@ mount "$P2" "$MNT_BOOTA"
 mount "$P3" "$MNT_BOOTB"
 mount "$P4" "$MNT_DATA"
 
-# --- Boot Control Partition (KSOLOCTL) ---
-# The RPi EEPROM loads start4.elf from partition 1.
-# autoboot.txt tells the firmware which partition has config.txt + kernel.
-echo "    Writing autoboot.txt + firmware to boot control partition..."
-cat > "$MNT_CTL/autoboot.txt" << 'AUTOBOOT'
-[all]
-tryboot_a_b=1
-boot_partition=2
-[tryboot]
-boot_partition=3
-AUTOBOOT
-
-# Minimal config.txt on partition 1 — firmware reads this BEFORE autoboot.txt
-# to determine arm_64bit mode and GPU settings. Without arm_64bit=1 here,
-# the firmware defaults to 32-bit and can't load our 64-bit kernel.
-cat > "$MNT_CTL/config.txt" << 'CFGTXT'
-arm_64bit=1
-enable_uart=1
-gpu_mem=16
-CFGTXT
-
-# Copy firmware blobs — REQUIRED on partition 1 for EEPROM to boot
-if ls "$RPI_FIRMWARE_DIR"/start*.elf 1>/dev/null 2>&1; then
-    cp "$RPI_FIRMWARE_DIR"/start*.elf "$MNT_CTL/"
-fi
-if ls "$RPI_FIRMWARE_DIR"/fixup*.dat 1>/dev/null 2>&1; then
-    cp "$RPI_FIRMWARE_DIR"/fixup*.dat "$MNT_CTL/"
-fi
-if [ -f "$RPI_FIRMWARE_DIR/bootcode.bin" ]; then
-    cp "$RPI_FIRMWARE_DIR/bootcode.bin" "$MNT_CTL/"
-fi
-
-# Copy DTBs to partition 1 — firmware may need them before redirecting
-if ls "$RPI_FIRMWARE_DIR"/bcm27*.dtb 1>/dev/null 2>&1; then
-    cp "$RPI_FIRMWARE_DIR"/bcm27*.dtb "$MNT_CTL/"
-fi
-if [ -d "$RPI_FIRMWARE_DIR/overlays" ]; then
-    cp -r "$RPI_FIRMWARE_DIR/overlays" "$MNT_CTL/"
-fi
-
 # --- Helper: populate a boot partition ---
 populate_boot_partition() {
     local MNT="$1"
@@ -231,6 +192,39 @@ CFGTXT
     echo "$VERSION" > "$MNT/version.txt"
 }
 
+# --- Boot Control Partition (KSOLOCTL) ---
+# Partition 1 serves dual purpose:
+#   1. Contains firmware + autoboot.txt for A/B redirect (if EEPROM supports it)
+#   2. Contains full boot files (kernel + initramfs) as fallback if autoboot.txt isn't supported
+echo "    Writing firmware + autoboot.txt + boot files to partition 1..."
+
+# autoboot.txt — tells firmware which partition to boot from (A/B switching)
+# If the EEPROM doesn't support this, it's silently ignored and the firmware
+# falls back to booting from partition 1 using config.txt below.
+cat > "$MNT_CTL/autoboot.txt" << 'AUTOBOOT'
+[all]
+tryboot_a_b=1
+boot_partition=2
+[tryboot]
+boot_partition=3
+AUTOBOOT
+
+# Copy firmware blobs — REQUIRED on partition 1 for EEPROM to boot
+if ls "$RPI_FIRMWARE_DIR"/start*.elf 1>/dev/null 2>&1; then
+    cp "$RPI_FIRMWARE_DIR"/start*.elf "$MNT_CTL/"
+fi
+if ls "$RPI_FIRMWARE_DIR"/fixup*.dat 1>/dev/null 2>&1; then
+    cp "$RPI_FIRMWARE_DIR"/fixup*.dat "$MNT_CTL/"
+fi
+if [ -f "$RPI_FIRMWARE_DIR/bootcode.bin" ]; then
+    cp "$RPI_FIRMWARE_DIR/bootcode.bin" "$MNT_CTL/"
+fi
+
+# Full boot files on partition 1 — fallback if autoboot.txt redirect doesn't work.
+# When autoboot.txt works, firmware switches to partition 2 and reads config.txt there.
+# When autoboot.txt is unsupported, firmware reads THIS config.txt and boots from here.
+populate_boot_partition "$MNT_CTL" "Boot Control (KSOLOCTL)"
+
 # --- Boot A Partition (KSOLOA) ---
 populate_boot_partition "$MNT_BOOTA" "Boot A (KSOLOA)"
 
@@ -248,7 +242,7 @@ sync
 echo ""
 echo "==> Raspberry Pi disk image created: $IMG_OUTPUT"
 echo "    Size: $(du -h "$IMG_OUTPUT" | cut -f1)"
-echo "    Part 1 (KSOLOCTL):  Firmware + autoboot.txt (boot control)"
+echo "    Part 1 (KSOLOCTL):  Firmware + kernel + initramfs + autoboot.txt (boot/control)"
 echo "    Part 2 (KSOLOA):    Boot A — kernel + initramfs + DTBs"
 echo "    Part 3 (KSOLOB):    Boot B — kernel + initramfs + DTBs"
 echo "    Part 4 (KSOLODATA): Persistent K8s state"