v0.7.0: Secure Boot chain, boot rules + decision webhook, tokenized answer files

Three features, all zero-toggle and principle-clean (single static musl
binary, container-first, no test certs, no client trust-store changes).

Secure Boot via signed shim+GRUB (automatic):
- The v0.6.1 escalation ladder gains a third rung: Firmware -> Builtin
  -> Shim. Secure-Boot firmware downloads our unsigned iPXE but refuses
  to execute it — indistinguishable from a failed chainload — so after
  two unconfirmed attempts the MAC is offered Fedora's Microsoft-signed
  shimx64.efi, which loads the signed GRUB, which fetches a
  server-rendered grub.cfg. Fully signed chain, SB stays on.
- scripts/fetch-shim.sh pulls shim-x64/grub2-efi-x64 (+aa64 best-effort)
  from the official Fedora 43 packages and ships the EFI binaries
  byte-for-byte unmodified; Dockerfile fetch stage gained rpm2cpio/cpio.
- New grub_script renderer (Linux kernel entries only — signed GRUB only
  boots signed kernels; sanboot/wimboot have no signed equivalent and
  are omitted with an explanatory menu line).
- TFTP server gains a DynamicAsset hook for server-rendered names
  (grub.cfg); HTTP serves the same config under /ipxe/grub.cfg for
  native UEFI HTTP Boot chains. Arch-aware fallback walks back down the
  ladder where no shim exists (BIOS, IA32).

Boot rules + decision webhook (open 'Matrix Boot'):
- Ordered first-match-wins rules over MAC prefix + client arch (the DHCP
  proxy now bakes arch into the boot.ipxe chain URL), generalizing
  per-MAC pins. Persisted to boot_rules.json; GET/PUT /api/boot-rules;
  rules editor + webhook field on the Hosts tab.
- Optional pixiecore-style webhook: unmatched boots GET
  <url>?mac=&arch= and 200 {"target":"id"} chains to it. Fail-open
  with a 2s budget — a dead endpoint can never block PXE.
- Decision order: exact pin -> rules -> webhook -> menu. Empty config
  is byte-for-byte the previous behavior.

Tokenized answer files (the post-WDS/CVE-2026-0386 hardening):
- Every generated unattended URL (inst.ks / preseed url / autoinstall
  seed) now carries a 4h boot-scoped token; /unattended/{id} and the
  cloud-init seed routes require it (or an operator session) once an
  admin exists. Stops answer-file credential harvesting by anything
  else on the network. No toggle; setup-mode installs stay open.

Validation: clippy clean, fmt clean, 290 workspace tests green
(+18 new across boot_tokens, boot_rules, arch ladder, escalation,
grub renderer, and four new full-flow integration tests).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

crates/openpxe/src/main.rs

@@ -191,6 +191,8 @@ async fn main() -> anyhow::Result<()> {
         queue: queue.clone(),
         hosts: hosts.clone(),
         boot_log: boot_log.clone(),
+        boot_rules: openpxe_core::BootRulesStore::load_or_default(&config.paths.work_dir),
+        boot_tokens: openpxe_core::BootTokens::new(),
         branding: branding.clone(),
         pxe_bg_cache: openpxe_http_api::state::PxeBgCache::default(),
         admin: admin.clone(),
@@ -230,11 +232,28 @@ async fn main() -> anyhow::Result<()> {
         Ok::<_, anyhow::Error>(())
     });
 
+    // v0.7.0: TFTP names that aren't embedded assets get a dynamic
+    // renderer — `grub.cfg` for the Secure Boot shim+GRUB chain is
+    // generated from the live boot-entry list on every fetch, so menu
+    // changes apply without restart.
+    let grub_isos = iso_store.clone();
+    let grub_base = public_base_url.clone();
+    let tftp_dynamic: openpxe_tftp::DynamicAsset = std::sync::Arc::new(move |name: &str| {
+        if name == "grub.cfg" || name.starts_with("grub.cfg-") {
+            Some(
+                openpxe_http_api::grub_script::render_grub_menu(&grub_isos.list(), &grub_base)
+                    .into_bytes(),
+            )
+        } else {
+            None
+        }
+    });
     let tftp = TftpServer::new(
         config.server.tftp_bind,
         config.server.tftp_port,
         clients.clone(),
         metrics.clone(),
+        Some(tftp_dynamic),
     );
     let tftp_task = tokio::spawn(tftp.run());