Refactor MCP tree server: dispatch table, caching, validation, subprocess cleanup

Break up the 1735-line handle_tool match into 45 individual handler functions
with hashtable-based dispatch. Add mtime-based file parse caching (AST + CST),
consolidated run_command helper replacing 9 bare open_process_in patterns,
require_file/require_dir input validation, and pagination (limit/offset) for
sx_find_across, sx_comp_list, sx_comp_usage. Also includes pending VM changes:
rest-arity support, hyperscript parser, compiler/transpiler updates.

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

sx/sx/handlers/hyperscript-api.sx

@@ -1,5 +1,4 @@
 ;; _hyperscript playground API handler
-;; Compiles hyperscript source and returns the AST + SX output as HTML
 
 (defhandler
   hs-compile
@@ -14,7 +13,7 @@
       (~tw :tokens "text-sm text-gray-400 italic")
       "Enter some hyperscript and click Compile.")
     (let
-      ((ast (hs-compile source)) (sx (hs-to-sx-from-source source)))
+      ((compiled (hs-to-sx-from-source source)))
       (div
         (~tw :tokens "space-y-4")
         (div
@@ -25,7 +24,7 @@
           (pre
             (~tw
               :tokens "bg-gray-900 text-green-400 p-4 rounded-lg text-sm overflow-x-auto whitespace-pre-wrap font-mono")
-            (sx-serialize sx)))
+            (sx-serialize compiled)))
         (div
           (h4
             (~tw
@@ -34,4 +33,4 @@
           (pre
             (~tw
               :tokens "bg-gray-900 text-amber-400 p-4 rounded-lg text-sm overflow-x-auto whitespace-pre-wrap font-mono")
-            (sx-serialize ast)))))))
+            (sx-serialize (hs-compile source))))))))