host: blog SPA scaffolding (WASM kernel) — server side complete, boost blocked on bundle rebuild

Turn the blog into a SPA using the SX-htmx engine (web/engine.sx) booting the
WASM OCaml kernel (same evaluator as the server) in-browser, with sx-boost
fragment-swapping every link into #content.

Server side DONE + verified:
- lib/host/static.sx: GET /static/** serves shared/static via the file-read
  primitive (ctype by ext, traversal-guarded, 404 on missing). Wired into
  serve.sh (module + route group). Tested: kernel JS + .wasm binary-exact.
- host/blog--page is now the SPA shell: full page = WASM boot scripts +
  sx-boost=#content wrapper + #content; on SX-Request:true returns ONLY the
  inner content fragment for the engine to swap. All 13 handlers thread req.
- docker-compose mounts ./shared/static.
- lib/host/playwright/spa-check.{spec.js,run-spa-check.sh}: boot/boost/swap/back.

Client side: the WASM kernel BOOTS (SxKernel object, data-sx-ready=true, web
stack loads). BLOCKER: the bundled .sxbc throw 'VM: unknown opcode 0' vs this
worktree's kernel -> .sx source fallback -> boot.sx source fails 'Expected
list, got string' -> process-boosted never binds links (boosted 0/N). Fix =
rebuild a consistent WASM bundle (recompile .sxbc against the kernel via
scripts/sx-build-all.sh); the browser wasm target isn't built here yet. See
plans/host-spa.md. Live NOT redeployed (stays on pre-SPA process).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.dev-sx-host.yml

@@ -39,6 +39,9 @@ services:
       - ./spec:/app/spec:ro
       - ./lib:/app/lib:ro
       - ./web:/app/web:ro
+      # Client assets for the blog SPA: the WASM OCaml kernel + sx-platform + the
+      # web-stack modules, served by lib/host/static.sx at /static/**.
+      - ./shared/static:/app/shared/static:ro
       # OCaml server binary — this worktree's build (has the SX_HTTP_HOST bind fix)
       - ./hosts/ocaml/_build/default/bin/sx_server.exe:/app/bin/sx_server:ro
       # Durable persist store (the SX op-log/kv on disk) — survives restarts.