Gate server-side component expansion with contextvar, fix nth arg order, add GEB essay and manifesto links

- Add _expand_components contextvar so _aser only expands components
  during page slot evaluation (fixes highlight on examples, avoids
  breaking fragment responses)
- Fix nth arg order (nth coll n) in docs.sx, examples.sx (delete-row,
  edit-row, bulk-update)
- Add "Godel, Escher, Bach and SX" essay with Wikipedia links
- Update SX Manifesto: new authors, Wikipedia links throughout,
  remove Marx/Engels link

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

shared/sx/async_eval.py

@@ -41,10 +41,18 @@ Usage::
 
 from __future__ import annotations
 
+import contextvars
 import inspect
 from typing import Any
 
 from .types import Component, Keyword, Lambda, Macro, NIL, StyleValue, Symbol
+
+# When True, _aser expands known components server-side instead of serializing
+# them for client rendering. Set during page slot evaluation so Python-only
+# helpers (e.g. highlight) in component bodies execute on the server.
+_expand_components: contextvars.ContextVar[bool] = contextvars.ContextVar(
+    "_expand_components", default=False
+)
 from .evaluator import _expand_macro, EvalError
 from .primitives import _PRIMITIVES
 from .primitives_io import IO_PRIMITIVES, RequestContext, execute_io
@@ -1058,6 +1066,24 @@ async def async_eval_slot_to_sx(
     """
     if ctx is None:
         ctx = RequestContext()
+
+    # Enable server-side component expansion for this slot evaluation.
+    # This lets _aser expand known components (so Python-only helpers
+    # like highlight execute server-side) instead of serializing them
+    # for client rendering.
+    token = _expand_components.set(True)
+    try:
+        return await _eval_slot_inner(expr, env, ctx)
+    finally:
+        _expand_components.reset(token)
+
+
+async def _eval_slot_inner(
+    expr: Any,
+    env: dict[str, Any],
+    ctx: RequestContext,
+) -> str:
+    """Inner implementation — runs with _expand_components=True."""
     # If expr is a component call, expand it through _aser
     if isinstance(expr, list) and expr:
         head = expr[0]
@@ -1159,13 +1185,14 @@ async def _aser(expr: Any, env: dict[str, Any], ctx: RequestContext) -> Any:
         if name.startswith("html:"):
             return await _aser_call(name[5:], expr[1:], env, ctx)
 
-        # Component call — expand macros, expand known components, serialize unknown
+        # Component call — expand macros, expand known components (in slot
+        # eval context only), serialize unknown
         if name.startswith("~"):
             val = env.get(name)
             if isinstance(val, Macro):
                 expanded = _expand_macro(val, expr[1:], env)
                 return await _aser(expanded, env, ctx)
-            if isinstance(val, Component):
+            if isinstance(val, Component) and _expand_components.get():
                 return await _aser_component(val, expr[1:], env, ctx)
             return await _aser_call(name, expr[1:], env, ctx)