Add real runtime materialization pipeline and bundle artifacts

runtime_sources/README.md

@@ -0,0 +1,29 @@
+# runtime_sources
+
+Source-of-truth inputs for `make runtime-bundle`.
+
+Current state:
+- `bin/firecracker` and `bin/jailer` are shim placeholders.
+- profile kernels and rootfs images are placeholder files.
+- `guest/pyro_guest_agent.py` is the guest agent artifact that should ultimately be installed into each real rootfs.
+- real source materialization now writes into `build/runtime_sources/`, not back into the tracked placeholder files.
+
+Materialization workflow:
+1. `make runtime-fetch-binaries`
+2. `make runtime-build-kernel-real`
+3. `make runtime-build-rootfs-real`
+4. `make runtime-bundle`
+
+Build requirements for the real path:
+- `docker`
+- outbound network access to GitHub and Debian snapshot mirrors
+- enough disk for a kernel build plus 2G ext4 images per profile
+
+Next steps to make the bundle guest-capable:
+1. Replace shim binaries with pinned official Firecracker and Jailer release artifacts.
+2. Replace placeholder `vmlinux` and `rootfs.ext4` files with real, bootable artifacts for each profile.
+3. Ensure the guest agent is installed and enabled inside every rootfs so the host can use vsock exec.
+4. Once the source artifacts are real, update `runtime.lock.json` component versions and flip capability flags from `false` to `true`.
+
+Safety rule:
+- The build pipeline should never emit `vm_boot=true`, `guest_exec=true`, or `guest_network=true` while any source artifact is still a shim or placeholder.