Fix signal-add-sub! losing subscribers after remove, fix build pipeline

signal-add-sub! used (append! subscribers f) which returns a new list
for immutable List but discards the result — after signal-remove-sub!
replaces the subscribers list via dict-set!, re-adding subscribers
silently fails. Counter island only worked once (0→1 then stuck).

Fix: use (dict-set! s "subscribers" (append ...)) to explicitly update
the dict field, matching signal-remove-sub!'s pattern.

Build pipeline fixes:
- sx-build-all.sh now bundles spec→dist and recompiles .sxbc bytecode
- compile-modules.js syncs .sx source files alongside .sxbc to wasm/sx/
- Per-file cache busting: wasm, platform JS, and sxbc each get own hash
- bundle.sh adds cssx.sx to dist

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

hosts/ocaml/browser/bundle.sh

@@ -65,6 +65,9 @@ cp "$ROOT/web/engine.sx"        "$DIST/sx/"
 cp "$ROOT/web/orchestration.sx" "$DIST/sx/"
 cp "$ROOT/web/boot.sx"          "$DIST/sx/"
 
+# 9. CSSX (stylesheet language)
+cp "$ROOT/sx/sx/cssx.sx"        "$DIST/sx/"
+
 # Summary
 WASM_SIZE=$(du -sh "$DIST/sx_browser.bc.wasm.assets" | cut -f1)
 JS_SIZE=$(du -sh "$DIST/sx_browser.bc.js" | cut -f1)

hosts/ocaml/browser/compile-modules.js

@@ -185,6 +185,7 @@ const staticSxDir = path.resolve(__dirname, '..', '..', '..', 'shared', 'static'
 if (fs.existsSync(staticSxDir)) {
   let copied = 0;
   for (const file of FILES) {
+    // Copy bytecode
     for (const ext of ['.sxbc', '.sxbc.json']) {
       const src = path.join(sxDir, file.replace(/\.sx$/, ext));
       const dst = path.join(staticSxDir, file.replace(/\.sx$/, ext));
@@ -193,6 +194,13 @@ if (fs.existsSync(staticSxDir)) {
         copied++;
       }
     }
+    // Also sync .sx source files (fallback when .sxbc missing)
+    const sxSrc = path.join(sxDir, file);
+    const sxDst = path.join(staticSxDir, file);
+    if (fs.existsSync(sxSrc) && !fs.lstatSync(sxSrc).isSymbolicLink()) {
+      fs.copyFileSync(sxSrc, sxDst);
+      copied++;
+    }
   }
   console.log('Copied', copied, 'files to', staticSxDir);
 }

hosts/ocaml/browser/sx-platform.js

@@ -180,8 +180,12 @@
 
   var _baseUrl = "";
 
-  // Detect base URL from current script
+  // Detect base URL and cache-bust params from current script tag.
+  // _cacheBust comes from the script's own ?v= query string (used for .sx source fallback).
+  // _sxbcCacheBust comes from data-sxbc-hash attribute — a separate content hash
+  // covering all .sxbc files so each file gets its own correct cache buster.
   var _cacheBust = "";
+  var _sxbcCacheBust = "";
   (function() {
     if (typeof document !== "undefined") {
       var scripts = document.getElementsByTagName("script");
@@ -191,6 +195,8 @@
           _baseUrl = src.substring(0, src.lastIndexOf("/") + 1);
           var qi = src.indexOf("?");
           if (qi !== -1) _cacheBust = src.substring(qi);
+          var sxbcHash = scripts[i].getAttribute("data-sxbc-hash");
+          if (sxbcHash) _sxbcCacheBust = "?v=" + sxbcHash;
           break;
         }
       }
@@ -233,7 +239,7 @@
    */
   function loadBytecodeFile(path) {
     var bcPath = path.replace(/\.sx$/, '.sxbc.json');
-    var url = _baseUrl + bcPath + _cacheBust;
+    var url = _baseUrl + bcPath + _sxbcCacheBust;
     try {
       var xhr = new XMLHttpRequest();
       xhr.open("GET", url, false);