live-image: fix firmware so i915 actually loads at boot

Previous attempt (c962d6d) added firmware-linux-nonfree to mkosi.conf,
but the CI bundle was still 63 MB and Tiger Lake wedged on tgl_guc.
Two reasons: (1) firmware-linux-nonfree on bookworm is a thin
metapackage that doesn't include firmware-misc-nonfree, which is where
i915 GuC/HuC blobs actually live; (2) Ubuntu's apt-packaged mkosi is
old enough that Repositories=non-free-firmware shorthand likely isn't
wired through to the debootstrap invocation, so firmware packages
silently miss the bootstrap step entirely.

Changes:
- Enumerate firmware packages explicitly in mkosi.conf (firmware-
  misc-nonfree, firmware-iwlwifi, firmware-realtek, firmware-amd-
  graphics, firmware-intel-sound, intel/amd64-microcode).
- Ship mkosi.sources.d/debian.sources with explicit deb822 so the
  non-free-firmware component is unambiguously available.
- Install mkosi 24.3 via pip in CI instead of apt's older build.
- Pin MODULES=most and COMPRESS=zstd via a tracked initramfs-tools
  config under mkosi.extra/.
- Narrow .gitignore so only the generated agent binary is ignored,
  not the whole mkosi.extra/ tree.
- New check-initrd Makefile target asserts both size (>=150 MB) and
  actual presence of i915/tgl_guc_*.bin inside the built initrd, so
  a silent firmware-drop regression fails the build loudly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

live-image/Makefile

@@ -12,9 +12,38 @@ REPO_ROOT := $(abspath ..)
 AGENT_BIN := $(REPO_ROOT)/bin/vetting-agent.linux-amd64
 MKOSI_EXTRA_AGENT := mkosi.extra/usr/local/sbin/vetting-agent
 
-.PHONY: all check-linux agent clean
+.PHONY: all check-linux check-initrd agent clean
 all: check-linux $(MKOSI_EXTRA_AGENT)
 	mkosi --force build
+	$(MAKE) check-initrd
+
+# Fail the build if the initrd doesn't actually contain the firmware
+# blobs we need. Catches two failure modes:
+#   1. Packages didn't install (apt/bootstrap component misconfigured) —
+#      the size check trips.
+#   2. Packages installed but update-initramfs didn't pack them
+#      (MODULES=dep regression, initramfs-tools default drift) — the
+#      blob presence check trips.
+# Requires unmkinitramfs (from initramfs-tools on the build host).
+check-initrd:
+	@size=$$(stat -c%s build/initrd.img); \
+	 min=$$((150 * 1024 * 1024)); \
+	 if [ "$$size" -lt "$$min" ]; then \
+	   echo "ERROR: initrd.img is $$size bytes (< $$min) — firmware almost certainly missing."; \
+	   echo "       Check mkosi build log for missing packages or apt failures."; \
+	   exit 1; \
+	 fi
+	@tmp=$$(mktemp -d); \
+	 trap 'rm -rf "$$tmp"' EXIT; \
+	 unmkinitramfs build/initrd.img "$$tmp" >/dev/null 2>&1 || { \
+	   echo "ERROR: unmkinitramfs failed — initrd.img may be corrupt."; exit 1; }; \
+	 if ! find "$$tmp" -path '*lib/firmware/i915/tgl_guc*' -print -quit | grep -q .; then \
+	   echo "ERROR: i915/tgl_guc firmware missing from initrd."; \
+	   echo "       Package installed but update-initramfs didn't pack /lib/firmware."; \
+	   echo "       Check MODULES= in /etc/initramfs-tools/initramfs.conf."; \
+	   exit 1; \
+	 fi
+	@echo "initrd.img OK ($$(du -h build/initrd.img | cut -f1), i915 firmware present)"
 
 agent: $(AGENT_BIN)
 
@@ -35,4 +64,5 @@ endif
 	@command -v mkosi >/dev/null 2>&1 || { echo "ERROR: mkosi not installed. Try: apt install mkosi"; exit 1; }
 
 clean:
-	rm -rf build mkosi.output mkosi.cache mkosi.extra
+	rm -rf build mkosi.output mkosi.cache
+	rm -f $(MKOSI_EXTRA_AGENT)