Data-first HO forms, fix plan pages, aser error handling (1080/1080)

Evaluator: data-first higher-order forms — ho-swap-args auto-detects
(map coll fn) vs (map fn coll), both work. Threading + HO: (-> data
(map fn)) dispatches through CEK HO machinery via quoted-value splice.
17 new tests in test-cek-advanced.sx.

Fix plan pages: add mother-language, isolated-evaluator, rust-wasm-host
to page-functions.sx plan() — were in defpage but missing from URL router.

Aser error handling: pages.py now catches EvalError separately, renders
visible error banner instead of silently sending empty content. All
except blocks include traceback in logs.

Scope primitives: register collect!/collected/clear-collected!/emitted/
emit!/context in shared/sx/primitives.py so hand-written _aser can
resolve them (fixes ~cssx/flush expansion failure).

New test file: shared/sx/tests/test_aser_errors.py — 19 pytest tests
for error propagation through all aser control flow forms.

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

sx/sx/page-functions.sx

@@ -541,6 +541,9 @@
         "sx-forge" '(~plans/sx-forge/plan-sx-forge-content)
         "sx-swarm" '(~plans/sx-swarm/plan-sx-swarm-content)
         "sx-proxy" '(~plans/sx-proxy/plan-sx-proxy-content)
+        "mother-language" '(~plans/mother-language/plan-mother-language-content)
+        "isolated-evaluator" '(~plans/isolated-evaluator/plan-isolated-evaluator-content)
+        "rust-wasm-host" '(~plans/rust-wasm-host/plan-rust-wasm-host-content)
         "async-eval-convergence" '(~plans/async-eval-convergence/plan-async-eval-convergence-content)
         "wasm-bytecode-vm" '(~plans/wasm-bytecode-vm/plan-wasm-bytecode-vm-content)
         "generative-sx" '(~plans/generative-sx/plan-generative-sx-content)

sx/sxc/pages/__init__.py

@@ -14,11 +14,20 @@ def setup_sx_pages() -> None:
 def _load_sx_page_files() -> None:
     """Load defpage definitions from sx/sxc/pages/*.sx."""
     import os
-    from shared.sx.pages import load_page_dir
+    from shared.sx.pages import load_page_dir, get_page_helpers
     from shared.sx.jinja_bridge import load_sx_dir, watch_sx_dir, load_service_components
     _sxc_dir = os.path.dirname(os.path.dirname(__file__))  # sx/sxc/
     service_root = os.path.dirname(_sxc_dir)               # sx/
     load_service_components(service_root, service_name="sx")
     load_sx_dir(_sxc_dir)
     watch_sx_dir(_sxc_dir)
+    # Register page helpers as primitives so the CEK machine can find them
+    # during nested async component expansion (e.g. highlight inside ~docs/code
+    # inside a plan component inside ~layouts/doc). Without this, the env_merge
+    # chain loses page helpers because component closures don't capture them.
+    from shared.sx.ref.sx_ref import PRIMITIVES
+    helpers = get_page_helpers("sx")
+    for name, fn in helpers.items():
+        PRIMITIVES[name] = fn
+    import logging; logging.getLogger("sx.pages").info("Injected %d page helpers as primitives: %s", len(helpers), list(helpers.keys())[:5])
     load_page_dir(os.path.dirname(__file__), "sx")