Add interactive tree editor island (Phase 4) + MCP server fixes

Phase 4: defisland ~sx-tools/tree-editor — interactive tree viewer
embedded in the SX Tools page. Features:
- Textarea with :bind for SX source input
- Parse button to re-parse on demand
- Tree view: annotated tree with path labels, clickable nodes
- Context view: enclosing chain from root to selected node
- Validate view: structural integrity checks (catches missing body etc.)

MCP server fixes: added ident-start?, ident-char?, make-keyword,
escape-string, sx-expr-source — needed by parser.sx when loaded
into the MCP evaluator.

Also: .mcp.json for Claude Code MCP server config, CLAUDE.md protocol
for structural .sx file editing.

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

hosts/ocaml/bin/mcp_tree.ml

@@ -61,6 +61,43 @@ let setup_env () =
   bind "identical?" (fun args -> match args with
     | [a; b] -> Bool (a == b)
     | _ -> Bool false);
+  (* Character classification for SX parser.sx *)
+  bind "ident-start?" (fun args -> match args with
+    | [String s] when String.length s = 1 ->
+      let c = s.[0] in
+      Bool ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
+            c = '_' || c = '~' || c = '*' || c = '+' || c = '-' ||
+            c = '>' || c = '<' || c = '=' || c = '/' || c = '!' ||
+            c = '?' || c = '&' || c = '@' || c = '^' || c = '%' ||
+            Char.code c > 127)
+    | _ -> Bool false);
+  bind "ident-char?" (fun args -> match args with
+    | [String s] when String.length s = 1 ->
+      let c = s.[0] in
+      Bool ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
+            (c >= '0' && c <= '9') ||
+            c = '_' || c = '~' || c = '*' || c = '+' || c = '-' ||
+            c = '>' || c = '<' || c = '=' || c = '/' || c = '!' ||
+            c = '?' || c = '&' || c = '.' || c = ':' || c = '#' ||
+            c = ',' || c = '@' || c = '^' || c = '%' ||
+            Char.code c > 127)
+    | _ -> Bool false);
+  bind "make-keyword" (fun args -> match args with
+    | [String s] -> Keyword s | _ -> Nil);
+  bind "escape-string" (fun args -> match args with
+    | [String s] ->
+      let buf = Buffer.create (String.length s) in
+      String.iter (fun c -> match c with
+        | '"' -> Buffer.add_string buf "\\\""
+        | '\\' -> Buffer.add_string buf "\\\\"
+        | '\n' -> Buffer.add_string buf "\\n"
+        | '\t' -> Buffer.add_string buf "\\t"
+        | '\r' -> Buffer.add_string buf "\\r"
+        | c -> Buffer.add_char buf c) s;
+      String (Buffer.contents buf)
+    | _ -> String "");
+  bind "sx-expr-source" (fun args -> match args with
+    | [SxExpr s] -> String s | _ -> String "");
   (* Runtime functions needed by tree-tools *)
   bind "symbol-name" (fun args -> match args with
     | [Symbol s] -> String s | _ -> String "");