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>

hosts/ocaml/lib/sx_primitives.ml

@@ -941,7 +941,19 @@ let () =
     | [f; Nil] -> call f []
     | _ -> raise (Eval_error "apply: function and list"));
   register "identical?" (fun args ->
-    match args with [a; b] -> Bool (a == b) | _ -> raise (Eval_error "identical?: 2 args"));
+    match args with
+    | [a; b] ->
+      (* Physical identity for reference types, structural for values.
+         Numbers/strings/booleans from different constant pools must
+         compare equal when their values match. *)
+      let identical = match a, b with
+        | Number x, Number y -> x = y
+        | String x, String y -> x = y  (* String.equal *)
+        | Bool x, Bool y -> x = y
+        | Nil, Nil -> true
+        | _ -> a == b  (* reference identity for dicts, lists, etc. *)
+      in Bool identical
+    | _ -> raise (Eval_error "identical?: 2 args"));
   register "make-spread" (fun args ->
     match args with
     | [Dict d] ->