host: Playwright check for the relate picker (+ 2 bugs it caught)

Wire a browser check for the picker, run it against an ephemeral host server,
and fix the two real bugs it surfaced.

- lib/host/playwright/relate-picker.spec.js — drives login-redirect-return,
  JS candidate load + infinite scroll, debounced filter, and click-to-relate
  (asserting the relation shows on the post page).
- lib/host/playwright/run-picker-check.sh — spins up an ephemeral host server
  (this worktree's binary + lib, temp persist), seeds a host post + 25
  candidates, runs the spec in the main worktree's Playwright/chromium, tears
  everything down. No live-site dependency, no live-data pollution. 4/4 pass.

Bugs the check caught:
1. Query params weren't %-decoded — dream's form parser decodes but its query
   parser doesn't, so a filter "Item 13" arrived as "Item%2013" and matched
   nothing. Fix: decode q with dream's own dr/url-decode in host/blog-relate-
   options. (+ conformance test for a spaced filter.)
2. A filter typed while a load was in flight got dropped (busy guard returned
   with no trailing fetch). Fix: a `pending` flag re-runs the load when the
   in-flight one finishes, coalescing to the latest query.

239/239 conformance; JS node --check clean. Verified live: spaced filter
returns matches; served JS carries the pending-reload fix.

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

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

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+# Browser check for the relate picker. Spins up an EPHEMERAL host server (this
+# worktree's binary + lib, a temp persist dir), seeds a host post + 25 candidates,
+# runs lib/host/playwright/relate-picker.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-picker-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="${PICKER_PORT:-8912}"
+PW_DIR="${PW_DIR:-/root/rose-ash}"          # worktree that has node_modules + chromium
+USER="admin"
+PASS="picker-check-pw"
+SECRET="picker-check-secret"
+PDIR=$(mktemp -d)
+JAR=$(mktemp)
+SPEC_SRC="lib/host/playwright/relate-picker.spec.js"
+SPEC_DST="$PW_DIR/tests/playwright/_picker-check.spec.js"
+SERVE_LOG=$(mktemp)
+
+cleanup() {
+  [ -n "${SVPID:-}" ] && kill "$SVPID" 2>/dev/null
+  # kill whatever is still bound to the port (serve.sh re-parents via `| exec`)
+  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) =="
+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 host post + 25 candidates =="
+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=Picker Host&sx_content=(p "host")&status=published'
+for n in $(seq -w 1 25); do
+  curl -s -b "$JAR" -o /dev/null -X POST "http://127.0.0.1:$PORT/new" \
+    --data "title=Picker Item $n&sx_content=(p \"item $n\")&status=published"
+done
+echo "== seeded ($(curl -s "http://127.0.0.1:$PORT/posts" | grep -o '"slug"' | wc -l) posts) =="
+
+echo "== running Playwright =="
+cp "$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 _picker-check.spec.js --workers=1 \
+  --config tests/playwright/playwright.config.js
+RC=$?
+
+echo "== done (exit $RC) =="
+exit $RC