Add js.sx bootstrapper docs page with G0 bug discovery writeup

Documents the self-hosting process for js.sx including the G0 bug
where Python's `if fn_expr` treated 0/False/"" as falsy, emitting
NIL instead of the correct value. Adds live verification page,
translation differences table, and nav entry.

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

sx/sxc/pages/docs.sx

@@ -459,6 +459,13 @@
           :g0-lines g0-lines
           :g0-bytes g0-bytes
           :verification-status verification-status)
+      "self-hosting-js"
+        (~bootstrapper-self-hosting-js-content
+          :js-sx-source js-sx-source
+          :defines-matched defines-matched
+          :defines-total defines-total
+          :js-sx-lines js-sx-lines
+          :verification-status verification-status)
       "python"
         (~bootstrapper-py-content
           :bootstrapper-source bootstrapper-source

sx/sxc/pages/helpers.py

@@ -230,7 +230,7 @@ def _bootstrapper_data(target: str) -> dict:
     """
     import os
 
-    if target not in ("javascript", "python", "self-hosting"):
+    if target not in ("javascript", "python", "self-hosting", "self-hosting-js"):
         return {"bootstrapper-not-found": True}
 
     ref_dir = os.path.join(os.path.dirname(__file__), "..", "..", "shared", "sx", "ref")
@@ -239,6 +239,8 @@ def _bootstrapper_data(target: str) -> dict:
 
     if target == "self-hosting":
         return _self_hosting_data(ref_dir)
+    if target == "self-hosting-js":
+        return _js_self_hosting_data(ref_dir)
 
     if target == "javascript":
         # Read bootstrapper source
@@ -353,6 +355,64 @@ def _self_hosting_data(ref_dir: str) -> dict:
     }
 
 
+def _js_self_hosting_data(ref_dir: str) -> dict:
+    """Run js.sx live: load into evaluator, translate spec files, diff against G0."""
+    import os
+    from shared.sx.parser import parse_all
+    from shared.sx.types import Symbol
+    from shared.sx.evaluator import evaluate, make_env
+    from shared.sx.ref.bootstrap_js import extract_defines, JSEmitter
+
+    try:
+        js_sx_path = os.path.join(ref_dir, "js.sx")
+        with open(js_sx_path, encoding="utf-8") as f:
+            js_sx_source = f.read()
+
+        exprs = parse_all(js_sx_source)
+        env = make_env()
+        for expr in exprs:
+            evaluate(expr, env)
+
+        emitter = JSEmitter()
+
+        # All spec files
+        all_files = sorted(
+            f for f in os.listdir(ref_dir) if f.endswith(".sx")
+        )
+        total = 0
+        matched = 0
+        for filename in all_files:
+            filepath = os.path.join(ref_dir, filename)
+            with open(filepath, encoding="utf-8") as f:
+                src = f.read()
+            defines = extract_defines(src)
+            for name, expr in defines:
+                g0_stmt = emitter.emit_statement(expr)
+                env["_def_expr"] = expr
+                g1_stmt = evaluate(
+                    [Symbol("js-statement"), Symbol("_def_expr")], env
+                )
+                total += 1
+                if g0_stmt.strip() == g1_stmt.strip():
+                    matched += 1
+
+        status = "identical" if matched == total else "mismatch"
+
+    except Exception as e:
+        js_sx_source = f";; error loading js.sx: {e}"
+        matched, total = 0, 0
+        status = "error"
+
+    return {
+        "bootstrapper-not-found": None,
+        "js-sx-source": js_sx_source,
+        "defines-matched": str(matched),
+        "defines-total": str(total),
+        "js-sx-lines": str(len(js_sx_source.splitlines())),
+        "verification-status": status,
+    }
+
+
 def _bundle_analyzer_data() -> dict:
     """Compute per-page component bundle analysis for the sx-docs app."""
     from shared.sx.jinja_bridge import get_component_env