host: extract the relate picker into a content-addressed ~relate-picker component

The declarative picker markup is now a reusable SX component
(lib/host/sx/relate-picker.sx, defcomp ~relate-picker &key slug kind) instead of
inline markup in the editor. It is a CONTENT-ADDRESSED, CLIENT-EXPANDED component:

- Server: on a full page load render-page expands ~relate-picker server-side
  (SEO / no-JS), exactly as before.
- Client: on a boosted SPA nav the edit body serialises to the compact
  (~relate-picker :slug … :kind …), and the CLIENT expands it. The component
  module is compiled to a content-addressed .sxbc, served immutably from
  /sx/h/{hash}, and listed in the page's data-sx-manifest "boot" array so the
  client eager-loads it after the web stack — registering its defcomp before any
  boosted fragment references it.

Wiring:
- lib/host/sx/relate-picker.sx — the component.
- lib/host/blog.sx — editor emits (~relate-picker :slug s :kind k); the inline
  form markup is gone.
- lib/host/static.sx — host/static-manifest-json emits boot:["relate-picker.sxbc"]
  (the previously-empty boot array, now used as designed).
- hosts/ocaml/browser/sx-platform.js — loadWebStack eager-loads the page manifest's
  boot[] modules (content-addressed) after the web stack.
- bundle.sh + compile-modules.js — copy/compile the component to .sxbc.
- serve.sh + conformance.sh — load the component module server-side.

This gives the host an app-component system: app defcomps shipped to the client by
hash, the same machinery as the kernel modules — the picker is the first, and it's
the model for publishing components externally.

Tests: conformance 272/272 (server expansion); relate-picker.spec.js 6/6 incl. the
boosted-nav populate (proves client-side component load + expansion) and the
error/retry case. WASM stack rebuilt (relate-picker.sxbc @ 6818110a).

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

shared/static/wasm/sx-platform.js

@@ -646,6 +646,18 @@
     // Load entry point itself (boot.sx — not a library, just defines + init)
     loadBytecodeFile("sx/" + entry.file) || loadSxFile("sx/" + entry.file.replace(/\.sxbc$/, '.sx'));
 
+    // App components: the page's data-sx-manifest "boot" array lists app-specific
+    // modules (e.g. ~relate-picker) to eager-load after the web stack, so their
+    // defcomps are registered before a boosted fragment references them. Loaded
+    // content-addressed, the same as any module.
+    var pageM = loadPageManifest();
+    if (pageM && pageM.boot && pageM.boot.length) {
+      for (var b = 0; b < pageM.boot.length; b++) {
+        var bf = pageM.boot[b];
+        loadBytecodeFile("sx/" + bf) || loadSxFile("sx/" + bf.replace(/\.sxbc$/, '.sx'));
+      }
+    }
+
     if (K.endModuleLoad) K.endModuleLoad();
     var count = Object.keys(_loadedLibs).length + 1; // +1 for entry
     var dt = Math.round(performance.now() - t0);

shared/static/wasm/sx/relate-picker.sx

@@ -0,0 +1,39 @@
+;; lib/host/sx/relate-picker.sx — the relate picker as a reusable, content-addressed
+;; SX component. On a FULL load render-page expands it server-side (SEO / no-JS); on a
+;; boosted SPA nav the edit body is serialized as `(~relate-picker :slug … :kind …)`
+;; and the CLIENT expands it — the component module is loaded content-addressed via
+;; the data-sx-manifest at boot, so its defcomp is registered before any fragment
+;; referencing it arrives.
+;;
+;; Pure markup, no client JS: the form GETs /<slug>/relate-options serialising kind +
+;; the filter q (a FORM is serialised on GET, a bare input is not), innerHTML-swapping
+;; the results <ul> on "load" and on a debounced "input". Paging is server-driven —
+;; each full page carries a "load more" sentinel (sx-trigger revealed) the endpoint
+;; emits. sx-retry makes a dropped/offline fetch self-heal; the engine's .sx-error
+;; class (styled by the host shell) surfaces a stuck retry. The engine re-binds these
+;; triggers on swapped-in content, so it works on full load AND boosted nav.
+(defcomp
+  ~relate-picker
+  (&key slug kind)
+  (form
+    :class "relate-picker"
+    :data-slug slug
+    :data-kind kind
+    :sx-get (str "/" slug "/relate-options")
+    :sx-trigger "input delay:200ms, load"
+    :sx-target (str "#rp-" kind "-results")
+    :sx-swap "innerHTML"
+    :sx-retry "exponential:1000:30000"
+    :style "margin:0"
+    (input :type "hidden" :name "kind" :value kind)
+    (input
+      :type "text"
+      :name "q"
+      :class "rp-filter"
+      :placeholder "filter…"
+      :autocomplete "off"
+      :style "width:100%;padding:0.4em;box-sizing:border-box")
+    (ul
+      :id (str "rp-" kind "-results")
+      :class "rp-results"
+      :style "list-style:none;padding:0;margin:0.5em 0;border:1px solid #ddd")))

shared/static/wasm/sx/relate-picker.sxbc

@@ -0,0 +1,3 @@
+(sxbc 1 "6818110a50d36c46"
+  (code
+    :constants ("eval-defcomp" (defcomp ~relate-picker (&key slug kind) (form :class "relate-picker" :data-slug slug :data-kind kind :sx-get (str "/" slug "/relate-options") :sx-trigger "input delay:200ms, load" :sx-target (str "#rp-" kind "-results") :sx-swap "innerHTML" :sx-retry "exponential:1000:30000" :style "margin:0" (input :type "hidden" :name "kind" :value kind) (input :type "text" :name "q" :class "rp-filter" :placeholder "filter…" :autocomplete "off" :style "width:100%;padding:0.4em;box-sizing:border-box") (ul :id (str "rp-" kind "-results") :class "rp-results" :style "list-style:none;padding:0;margin:0.5em 0;border:1px solid #ddd")))) :bytecode (20 0 0 1 1 0 48 1 50)))