host: blog persisted in durable SX store + materialised view, 158/158

Blog posts now live in the durable SX store (persist/durable-backend, on-disk
under $SX_PERSIST_DIR — already built: sx_persist_store.ml + lib/persist/
durable.sx). Publishing appends insert ops to the slug's content stream; posts
survive restarts (verified: seq/log stable across container restart, re-seed
idempotent).

Read path: http-listen handlers can't drive per-request perform/IO (sx_call
doesn't resolve the CEK IO suspension the way the main loop does), so posts are
materialised from the store into an in-memory view at boot (host/blog-load-all!
+ host/blog-seed!) and request handlers read the view — perform-free. Store is
source of truth; view is a boot-rebuilt cache.

Deploy: docker-compose.dev-sx-host.yml mounts /root/sx-host-persist (chowned to
appuser 10001) at /data/persist; SX_PERSIST_DIR set. blog.rose-ash.com/welcome/
live. Per-request-IO kernel fix tracked in the plan as the next task.

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

lib/host/serve.sh

@@ -75,6 +75,8 @@ MODULES=(
   "lib/content/doc.sx"
   "lib/content/render.sx"
   "lib/content/api.sx"
+  "lib/content/store.sx"
+  "lib/persist/durable.sx"
   "lib/dream/types.sx"
   "lib/dream/json.sx"
   "lib/dream/auth.sx"
@@ -95,10 +97,20 @@ EPOCH=1
   for M in "${MODULES[@]}"; do
     echo "(epoch $EPOCH)"; echo "(load \"$M\")"; EPOCH=$((EPOCH+1))
   done
-  # Seed a welcome post so blog.rose-ash.com/welcome/ renders live (until posts
-  # arrive from a persist-backed content store).
+  # Point the blog at the DURABLE file backend (persists under $SX_PERSIST_DIR),
+  # then idempotently seed a welcome post — re-seeding is a no-op if it already
+  # exists on disk, so restarts don't duplicate blocks.
   echo "(epoch $EPOCH)"
-  echo "(eval \"(host/blog-register! \\\"welcome\\\" (host/blog-make \\\"welcome\\\" \\\"Welcome to the SX host\\\" \\\"This page is rendered by lib/host on the SX runtime — no Quart.\\\"))\")"
+  echo "(eval \"(host/blog-use-store! (persist/durable-backend))\")"
+  EPOCH=$((EPOCH+1))
+  echo "(epoch $EPOCH)"
+  # Materialise any persisted posts into the in-memory view, then ensure the
+  # welcome post exists (idempotent). Both run on the main thread (IO is fine
+  # here; request handlers only read the view).
+  echo "(eval \"(host/blog-load-all!)\")"
+  EPOCH=$((EPOCH+1))
+  echo "(epoch $EPOCH)"
+  echo "(eval \"(host/blog-seed! \\\"welcome\\\" \\\"Welcome to the SX host\\\" \\\"This page is rendered by lib/host on the SX runtime, persisted in the SX store — no Quart.\\\" 1)\")"
   EPOCH=$((EPOCH+1))
   echo "(epoch $EPOCH)"
   # Anonymous read endpoints: feed timeline + relations container reads + blog