Reactive island preservation across server-driven morphs

Islands survive hypermedia swaps: morph-node skips hydrated
data-sx-island elements when the same island exists in new content.
dispose-islands-in skips hydrated islands to prevent premature cleanup.

- @client directive: .sx files marked ;; @client send define forms to browser
- CSSX client-side: cssxgroup renamed (no hyphen) to avoid isRenderExpr
  matching it as a custom element — was producing [object HTMLElement]
- Island wrappers: div→span to avoid block-in-inline HTML parse breakage
- ~sx-header is now a defisland with inline reactive colour cycling
- bootstrap_js.py defaults output to shared/static/scripts/sx-browser.js
- Deleted stale sx-ref.js (sx-browser.js is the canonical browser build)
- Hegelian Synthesis essay: dialectic of hypertext and reactivity
- component-source helper handles Island types for docs pretty-printing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/boot.sx

@@ -400,12 +400,19 @@
 
 (define dispose-islands-in
   (fn (root)
-    ;; Dispose all islands within root before a swap replaces them.
+    ;; Dispose islands within root, but SKIP hydrated islands —
+    ;; they may be preserved across morphs. Only dispose islands
+    ;; that are not currently hydrated (e.g. freshly parsed content
+    ;; being discarded) or that have been explicitly detached.
     (when root
       (let ((islands (dom-query-all root "[data-sx-island]")))
         (when (and islands (not (empty? islands)))
-          (log-info (str "disposing " (len islands) " island(s)"))
-          (for-each dispose-island islands))))))
+          (let ((to-dispose (filter
+                  (fn (el) (not (is-processed? el "island-hydrated")))
+                  islands)))
+            (when (not (empty? to-dispose))
+              (log-info (str "disposing " (len to-dispose) " island(s)"))
+              (for-each dispose-island to-dispose))))))))
 
 
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