Content-addressed on-demand loading: Merkle DAG for all browser assets

Replace the monolithic 500KB <script data-components> block with a 25KB
JSON manifest mapping names to content hashes. Every definition —
components, islands, macros, client libraries, bytecode modules, and
WASM binaries — is now content-addressed and loaded on demand.

Server (sx_server.ml):
- build_hash_index: Merkle DAG over all definitions — topological sort,
  hash leaves first, component refs become @h:{hash} in instantiated form
- /sx/h/{hash} endpoint: serves definitions with Cache-Control: immutable
- Per-page manifest in <script data-sx-manifest> with defs + modules + boot
- Client library .sx files hashed as whole units (tw.sx, tw-layout.sx, etc.)
- .sxbc modules and WASM kernel hashed individually

Browser (sx-platform.js):
- Content-addressed boot: inline script loads kernel + platform by hash
- loadDefinitionByHash: recursive dep resolution with @h: rewriting
- resolveHash: 3-tier cache (memory → localStorage → fetch /sx/h/{hash})
- __resolve-symbol extended for manifest-based component + library loading
- Cache API wrapper intercepts .wasm fetches for offline caching
- Eager pre-loading of plain symbol deps for CEK evaluator compatibility

Shell template (shell.sx):
- Monolithic <script data-components> removed
- data-sx-manifest script with full hash manifest
- Inline bootstrap replaces <script src="...?v="> with CID-based loading

Second visit loads zero bytes from network. Changed content gets a new
hash — only that item refetched (Merkle propagation).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/sx/templates/shell.sx

@@ -7,6 +7,7 @@
     (sx-css :as string?)
     (component-hash :as string?)
     (component-defs :as string?)
+    (component-manifest :as string?)
     (pages-sx :as string?)
     (page-sx :as string?)
     (body-html :as string?)
@@ -61,11 +62,12 @@
         (style
           (raw!
             "[data-sx-island] button,[data-sx-island] a,[data-sx-island] [role=button]{cursor:pointer}"))
-        (script
-          :type "text/sx"
-          :data-components true
-          :data-hash component-hash
-          (raw! (or component-defs "")))
+        (when
+          component-manifest
+          (script
+            :type "application/json"
+            :data-sx-manifest true
+            (raw! component-manifest)))
         (when
           init-sx
           (script :type "text/sx" :data-init true (raw! init-sx)))
@@ -74,12 +76,6 @@
           :type "text/sx"
           :data-mount "#sx-root"
           (raw! (or page-sx "")))
-        (<>
-          (script
-            :src (str
-              asset-url
-              "/wasm/sx_browser.bc.wasm.js?v="
-              (or wasm-hash "0")))
-          (script
-            :src (str asset-url "/wasm/sx-platform.js?v=" (or platform-hash "0"))
-            :data-sxbc-hash (or sxbc-hash "0")))))))
+        (script
+          (raw!
+            "\n(function(){\n  var m=document.querySelector('[data-sx-manifest]');\n  if(!m)return;\n  var j=JSON.parse(m.textContent);\n\n  // Cache API wrapper — intercept .wasm fetches for offline caching.\n  if(typeof caches!=='undefined'){\n    var _fetch=window.fetch;\n    var CACHE='sx-wasm-v1';\n    window.fetch=function(input,init){\n      var url=(typeof input==='string')?input:\n              (input instanceof URL)?input.href:\n              (input&&input.url)||'';\n      if(url.indexOf('.wasm')!==-1){\n        return caches.open(CACHE).then(function(c){\n          return c.match(url).then(function(r){\n            if(r)return r;\n            return _fetch(input,init).then(function(resp){\n              if(resp.ok)c.put(url,resp.clone());\n              return resp;\n            });\n          });\n        });\n      }\n      return _fetch(input,init);\n    };\n  }\n\n  // Content-addressed boot: load kernel + platform by hash\n  if(!j.boot)return;\n  j.boot.forEach(function(h){\n    var s=document.createElement('script');\n    s.src='/sx/h/'+h;\n    document.head.appendChild(s);\n  });\n})();\n"))))))