The sweep is behind @js, because dune test stays fast

The alias is @x86's shape and deps: one rule over spike/js/survey.sh, FLAN
passed so the script does not start a dune inside dune's own lock. It is not
in the default run and node is probed rather than assumed.

test/dune

@@ -331,4 +331,46 @@
  (deps
   (alias page)
   (alias x86)
+  (alias js)
   (alias cells)))
+
+; The JS dialect's sweep, opt-in in the same way and for the same reason:
+;
+;     dune build --root . @js
+;
+; Shaped after @x86 above, deps and all, because it walks the same corpus.
+; Two differences. It needs node, which the script probes for and reports on
+; rather than failing over -- this is opt-in, and a machine without node
+; should say so and stop, not report zero of everything. And SURVEY_STRICT
+; means something narrower here: a refusal is a *decision* in a dialect, not
+; a gap, so only a DIFFER and a CRASH fail the alias. See the header of
+; spike/js/survey.sh.
+(rule
+ (alias js)
+ (deps
+  (file %{workspace_root}/spike/js/survey.sh)
+  (glob_files %{workspace_root}/spike/js/*.flan)
+  (file %{workspace_root}/bin/main.exe)
+  (file %{workspace_root}/calc-me.flan)
+  (file %{workspace_root}/sand.flan)
+  (file %{workspace_root}/brush.png)
+  (glob_files %{workspace_root}/vendor/raylib/*)
+  (glob_files %{workspace_root}/vendor/agent/*)
+  (glob_files %{workspace_root}/vendor/edn/*)
+  (glob_files %{workspace_root}/examples/*)
+  (glob_files programs/*.flan)
+  (glob_files programs/assets/*)
+  (glob_files programs/pkgs/shape/*)
+  (glob_files programs/pkgs/area/*)
+  (glob_files programs/pkgs/draw/*)
+  (glob_files programs/pkgs/ring-a/*)
+  (glob_files programs/pkgs/ring-b/*)
+  (glob_files programs/pkgs/ring-c/*)
+  (glob_files programs/pkgs/mac/*)
+  (glob_files programs/pkgs/macring/*)
+  (glob_files programs/pkgs/macspin/*))
+ (action
+  (setenv SURVEY_STRICT 1
+   (setenv SURVEY_QUIET 1
+    (setenv FLAN %{workspace_root}/bin/main.exe
+     (run bash %{workspace_root}/spike/js/survey.sh))))))