Merge lab into refactor/split-style-css

tests/helpers/stylesheets.py

@@ -1,11 +1,11 @@
 """Read the app's CSS the way the browser does.
 
-``static/style.css`` no longer holds every rule: panel styles live in separate
-files that ``static/index.html`` loads eagerly, in a fixed order, right after
-it. The cascade is the concatenation of those files in that order.
+The former ``static/style.css`` is now an ordered set of numbered fragments,
+followed by the existing panel stylesheets. ``static/index.html`` loads the
+complete cascade eagerly in the order the browser must apply it.
 
-A test that asserts on a rule must therefore look at all of them. Reading
-``static/style.css`` alone ties the test to whichever file a rule happens to
+A test that asserts on a rule must therefore look at the complete cascade.
+Reading one fragment alone ties the test to whichever file a rule happens to
 sit in today, so it goes red the next time a rule moves without anything about
 the rendered page having changed.
 """
@@ -53,8 +53,7 @@ def stylesheet_urls() -> list[str]:
 
 
 def stylesheet_link_tags() -> str:
-    """The <link> tags to drop into a synthetic page so it gets the whole
-    cascade, not just style.css."""
+    """The <link> tags for a synthetic page that needs the whole cascade."""
     return "".join(f'<link rel="stylesheet" href="{u}">' for u in stylesheet_urls())
 
 
@@ -68,8 +67,8 @@ def stylesheet_cache_version() -> str:
 
     The stylesheet is split across several files that must be busted together:
     shipping one fragment under a stale token serves a browser half of an old
-    cascade and half of a new one. Tests that used to read the version off
-    ``style.css`` ask for it here instead, so they keep checking the invariant
+    cascade and half of a new one. Tests ask for the shared version here instead of deriving it from one
+    stylesheet filename, so they keep checking the invariant
     rather than a filename.
     """
     versions = set()