host: block editor live-swap — :sx-post (not sx-disable) + a Playwright check

The block-editor move/remove controls used :sx-disable "true" (the OLD relate-picker pattern
= plain POST → 303 → full reload). Switched to :sx-post + :sx-target #block-editor + :sx-swap
outerHTML (the current pattern): the click is a text/sx form round-trip through the WASM
engine, the handler returns the re-rendered #block-editor, and it swaps IN PLACE — no reload.

Added lib/host/playwright/{block-editor.spec.js, run-block-check.sh} (the run-picker-check
harness pattern: ephemeral host server + one editable post + the main worktree's chromium).
Verifies the irreducibly-browser behaviour the SX conformance can't see: adding, reordering
(↑), and removing blocks re-render #block-editor live, and the controls RE-BIND on the
content each swap brings in. PASSES (1/1, 16s). blog conformance still 165/165.

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

lib/host/playwright/run-block-check.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# Browser check for the BLOCK EDITOR (composition step 6). Spins up an EPHEMERAL host
+# server (this worktree's binary + lib, a temp persist dir), seeds ONE editable host post,
+# runs lib/host/playwright/block-editor.spec.js in the main worktree's Playwright, then
+# tears everything down. No live-site dependency, no live-data pollution.
+#
+#   bash lib/host/playwright/run-block-check.sh
+#
+# Requires: the OCaml binary built (hosts/ocaml/_build/default/bin/sx_server.exe)
+# and Playwright + chromium in /root/rose-ash (the architecture worktree).
+set -uo pipefail
+cd "$(git rev-parse --show-toplevel)"
+ROOT=$(pwd)
+
+PORT="${BLOCK_PORT:-8913}"
+PW_DIR="${PW_DIR:-/root/rose-ash}"          # worktree that has node_modules + chromium
+USER="admin"
+PASS="block-check-pw"
+SECRET="block-check-secret"
+PDIR=$(mktemp -d)
+JAR=$(mktemp)
+SPEC_SRC="lib/host/playwright/block-editor.spec.js"
+SPEC_DST="$PW_DIR/tests/playwright/_block-check.spec.js"
+SERVE_LOG=$(mktemp)
+
+cleanup() {
+  [ -n "${SVPID:-}" ] && kill "$SVPID" 2>/dev/null
+  local pid
+  pid=$(ss -lptn "sport = :$PORT" 2>/dev/null | grep -oE 'pid=[0-9]+' | head -1 | cut -d= -f2)
+  [ -n "$pid" ] && kill "$pid" 2>/dev/null
+  rm -f "$SPEC_DST" "$JAR" "$SERVE_LOG"
+  rm -rf "$PDIR"
+}
+trap cleanup EXIT
+
+echo "== starting ephemeral host server on :$PORT (persist=$PDIR) =="
+# SX_SERVING_JIT=1 matches the live container (gates the http-listen IO resolver).
+SX_SERVING_JIT=1 HOST_PORT="$PORT" SX_PERSIST_DIR="$PDIR" \
+  SX_ADMIN_USER="$USER" SX_ADMIN_PASSWORD="$PASS" SX_SESSION_SECRET="$SECRET" \
+  bash lib/host/serve.sh >"$SERVE_LOG" 2>&1 &
+SVPID=$!
+
+for i in $(seq 1 60); do
+  curl -sf -o /dev/null "http://127.0.0.1:$PORT/health" 2>/dev/null && break
+  sleep 1
+  [ "$i" = "60" ] && { echo "server never came up:"; cat "$SERVE_LOG"; exit 1; }
+done
+echo "== server up =="
+
+echo "== seeding 1 editable host post (block-host) =="
+curl -s -c "$JAR" -o /dev/null -X POST "http://127.0.0.1:$PORT/login" \
+  --data "username=$USER&password=$PASS"
+curl -s -b "$JAR" -o /dev/null -X POST "http://127.0.0.1:$PORT/new" \
+  --data 'title=Block Host&sx_content=(p "host")&status=published'
+
+echo "== running Playwright =="
+cp "$ROOT/$SPEC_SRC" "$SPEC_DST"
+cd "$PW_DIR"
+SX_TEST_URL="http://127.0.0.1:$PORT" SX_ADMIN_USER="$USER" SX_ADMIN_PASSWORD="$PASS" \
+  node_modules/.bin/playwright test _block-check.spec.js --workers=1 \
+  --config tests/playwright/playwright.config.js
+RC=$?
+
+echo "== done (exit $RC) =="
+exit $RC