host: per-request IO kernel fix + fully-dynamic blog (no cache), 159/159

KERNEL (sx_server.ml): route http-listen handlers through cek_run_with_io
instead of bare Sx_runtime.sx_call, so handlers resolve per-request IO
(durable persist reads/writes) via the same IO-driving runner the REPL uses.
Verified: per-request read+write, 10 concurrent writes (15 on disk, no
corruption), handler errors don't crash the server, http contract 6/6.

BLOG: fully dynamic — host/blog-post reads the post from the durable store
(content/head) AND renders (content/html) per request, no in-memory view, no
cached output. Possible because of the IO fix. Honest ~2s due to interpreted
Smalltalk render.

Render speed is NOT solved here: the JIT (precompiler) isn't installed in the
serving mode and currently miscompiles the Smalltalk evaluator's nested ASTs
(enabling it breaks ~60% of tests). Fixing the JIT is a separate, high-payoff
effort. Documented in the plan.

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

hosts/ocaml/bin/sx_server.ml

@@ -814,7 +814,15 @@ let setup_evaluator_bridge env =
              Hashtbl.replace req "body" (String body);
              Mutex.lock mtx;
              let resp =
-               (try Sx_runtime.sx_call handler [Dict req]
+               (* Run the handler through the IO-aware CEK runner (not bare
+                  sx_call) so request handlers can perform per-request IO —
+                  durable store reads/writes resolve via cek_run_with_io's
+                  suspension loop instead of returning an unresolved suspension. *)
+               (try
+                  let st = Sx_ref.continue_with_call handler
+                             (List [Dict req]) (Env (Sx_types.make_env ()))
+                             (List [Dict req]) (List []) in
+                  cek_run_with_io st
                 with e -> Mutex.unlock mtx; raise e) in
              Mutex.unlock mtx;
              let getk k = match resp with