Fix WASM browser click handlers: 8 bugs, 50 new VM tests

The sx-get links were doing full page refreshes because click handlers
never attached. Root causes: VM frame management bug, missing primitives,
CEK/VM type dispatch mismatch, and silent error swallowing.

Fixes:
- VM frame exhaustion: frames <- [] now properly pops to rest_frames
- length primitive: add alias for len in OCaml primitives
- call_sx_fn: use sx_call directly instead of eval_expr (CEK checks
  for type "lambda" but VmClosure reports "function")
- Boot error surfacing: Sx.init() now has try/catch + failure summary
- Callback error surfacing: catch-all handler for non-Eval_error exceptions
- Silent JIT failures: log before CEK fallback instead of swallowing
- vm→env sync: loadModule now calls sync_vm_to_env()
- sx_build_bytecode MCP tool added for bytecode compilation

Tests: 50 new tests across test-vm.sx and test-vm-primitives.sx covering
nested VM calls, frame integrity, CEK bridge, primitive availability,
cross-module symbol resolution, and callback dispatch.

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

hosts/ocaml/bin/mcp_tree.ml

@@ -519,6 +519,21 @@ let rec handle_tool name args =
      | Unix.WEXITED 0 -> text_result (Printf.sprintf "OK — %s build succeeded\n%s" target (String.trim output))
      | _ -> error_result (Printf.sprintf "%s build failed:\n%s" target output))
 
+  | "sx_build_bytecode" ->
+    let project_dir = try Sys.getenv "SX_PROJECT_DIR" with Not_found ->
+      let spec_dir = try Sys.getenv "SX_SPEC_DIR" with Not_found -> "spec" in
+      Filename.dirname spec_dir
+    in
+    let cmd = Printf.sprintf "cd %s && node hosts/ocaml/browser/compile-modules.js shared/static/wasm 2>&1" project_dir in
+    let ic = Unix.open_process_in cmd in
+    let lines = ref [] in
+    (try while true do lines := input_line ic :: !lines done with End_of_file -> ());
+    let status = Unix.close_process_in ic in
+    let output = String.concat "\n" (List.rev !lines) in
+    (match status with
+     | Unix.WEXITED 0 -> text_result (Printf.sprintf "OK — bytecode compilation succeeded\n%s" (String.trim output))
+     | _ -> error_result (Printf.sprintf "Bytecode compilation failed:\n%s" output))
+
   | "sx_test" ->
     let host = args |> member "host" |> to_string_option |> Option.value ~default:"js" in
     let full = args |> member "full" |> to_bool_option |> Option.value ~default:false in
@@ -748,8 +763,10 @@ let rec handle_tool name args =
         (match actions with Some a -> Some ("actions", `String a) | None -> None);
         (match island with Some i -> Some ("island", `String i) | None -> None);
       ]) in
-      let args_json = Yojson.Safe.to_string (Yojson.Safe.from_string (Yojson.Basic.to_string inspector_args)) in
-      let cmd = Printf.sprintf "cd %s && node tests/playwright/sx-inspect.js '%s' 2>&1" project_dir (String.escaped args_json) in
+      let args_json = Yojson.Basic.to_string inspector_args in
+      (* Single-quote shell wrapping — escape any literal single quotes in JSON *)
+      let shell_safe = String.concat "'\\''" (String.split_on_char '\'' args_json) in
+      let cmd = Printf.sprintf "cd %s && node tests/playwright/sx-inspect.js '%s' 2>&1" project_dir shell_safe in
       let ic = Unix.open_process_in cmd in
       let lines = ref [] in
       (try while true do lines := input_line ic :: !lines done with End_of_file -> ());
@@ -1304,6 +1321,8 @@ let tool_definitions = `List [
     [("target", `Assoc [("type", `String "string"); ("description", `String "Build target: \"js\" (default) or \"ocaml\"")]);
      ("full", `Assoc [("type", `String "boolean"); ("description", `String "Include extensions and type system (default: false)")])]
     [];
+  tool "sx_build_bytecode" "Compile all web .sx files to pre-compiled .sxbc.json bytecode modules for the WASM browser kernel."
+    [] [];
   tool "sx_test" "Run SX test suite. Returns pass/fail summary and any failures."
     [("host", `Assoc [("type", `String "string"); ("description", `String "Test host: \"js\" (default) or \"ocaml\"")]);
      ("full", `Assoc [("type", `String "boolean"); ("description", `String "Run full test suite including extensions (default: false)")])]
@@ -1354,13 +1373,13 @@ let tool_definitions = `List [
      ("files", `Assoc [("type", `String "array"); ("items", `Assoc [("type", `String "string")]); ("description", `String "Multiple .sx files to load in order")]);
      ("setup", `Assoc [("type", `String "string"); ("description", `String "SX setup expression to run before main evaluation")])]
     ["expr"];
-  tool "sx_playwright" "Run Playwright browser tests or inspect SX pages interactively. Modes: run (spec files), inspect (page/island report with leak detection and handler audit), diff (full SSR vs hydrated DOM), hydrate (lake-focused SSR vs hydrated comparison — detects clobbering), eval (JS expression), interact (action sequence), screenshot."
+  tool "sx_playwright" "Run Playwright browser tests or inspect SX pages interactively. Modes: run (spec files), inspect (page/island report with leak detection and handler audit), diff (full SSR vs hydrated DOM), hydrate (lake-focused SSR vs hydrated comparison — detects clobbering), eval (JS expression), interact (action sequence), screenshot, listeners (CDP event listener inspection), trace (click + capture console/network/pushState), cdp (raw CDP command)."
     [("spec", `Assoc [("type", `String "string"); ("description", `String "Spec file to run (run mode). e.g. stepper.spec.js")]);
-     ("mode", `Assoc [("type", `String "string"); ("description", `String "Mode: run, inspect, diff, hydrate, eval, interact, screenshot")]);
+     ("mode", `Assoc [("type", `String "string"); ("description", `String "Mode: run, inspect, diff, hydrate, eval, interact, screenshot, listeners, trace, cdp")]);
      ("url", `Assoc [("type", `String "string"); ("description", `String "URL path to navigate to (default: /)")]);
      ("island", `Assoc [("type", `String "string"); ("description", `String "Filter inspect to a specific island by name (e.g. home/stepper)")]);
-     ("selector", `Assoc [("type", `String "string"); ("description", `String "CSS selector to focus on (screenshot mode)")]);
-     ("expr", `Assoc [("type", `String "string"); ("description", `String "JS expression to evaluate (eval mode)")]);
+     ("selector", `Assoc [("type", `String "string"); ("description", `String "CSS selector for screenshot/listeners/trace modes")]);
+     ("expr", `Assoc [("type", `String "string"); ("description", `String "JS expression (eval mode), selector (listeners/trace), or CDP command (cdp mode)")]);
      ("actions", `Assoc [("type", `String "string"); ("description", `String "Semicolon-separated action sequence (interact mode). Actions: click:sel, fill:sel:val, wait:ms, text:sel, html:sel, attrs:sel, screenshot, screenshot:sel, count:sel, visible:sel")])]
     [];
 ]