test(css): read the static origin at call time, not at import

The snapshot harness read ODYSSEUS_TEST_STATIC_ORIGIN into a module constant.
That env var is published by the session static-server fixture, which runs
after collection has already imported the module, so the constant always held
the 7011 fallback and the capture connected to a port nothing was listening on:

    route.fetch: connect ECONNREFUSED 127.0.0.1:7011

Neither branch is wrong on its own. The harness was written while the fixture
still bound a fixed 7011, and the ephemeral-port change removed that port. The
two only disagree once they are in the same tree, which is what this integration
branch is for.

With this, the baseline recorded before the stylesheet split is reproduced
exactly after it, so the split is confirmed to preserve computed styles rather
than only argued to.

tests/test_css_computed_style_snapshot.py

@@ -24,10 +24,17 @@ _requires_browser = pytest.mark.skipif(
     reason="node with the playwright package is required (npm ci)",
 )
 
-# The session static server publishes its ephemeral origin here. The literal
-# fallback is the fixed port the fixture used before it moved to an ephemeral
-# one, so this module works on either revision.
-STATIC_ORIGIN = os.environ.get("ODYSSEUS_TEST_STATIC_ORIGIN", "http://127.0.0.1:7011")
+def static_origin() -> str:
+    """Origin of the session static server, read at call time.
+
+    The session fixture binds an ephemeral port and publishes it through the
+    environment, which happens after this module is imported at collection.
+    Reading it into a module constant therefore captured the fallback and the
+    capture then connected to a port nothing was listening on. The literal
+    fallback is the fixed port the fixture used before it moved to an ephemeral
+    one, so this still works on a revision that predates that change.
+    """
+    return os.environ.get("ODYSSEUS_TEST_STATIC_ORIGIN", "http://127.0.0.1:7011")
 
 # One conflicting selector used to prove the harness is actually sensitive to
 # source order. `.attach-strip` is declared three times at the top level of
@@ -62,7 +69,7 @@ def test_baseline_covers_every_inventory_entry():
 
 @_requires_browser
 def test_computed_styles_match_the_committed_baseline():
-    captured = snapshot.capture(STATIC_ORIGIN)
+    captured = snapshot.capture(static_origin())
 
     assert captured["missing"] == {}, (
         "inventory entries matched no element - the markup moved under the "
@@ -91,10 +98,10 @@ def test_reordering_two_conflicting_declarations_moves_the_digest():
     """
     variants = ["desktop-dark-comfortable"]
     unchanged = snapshot.summarize(
-        snapshot.capture(STATIC_ORIGIN, variants=variants)["snapshot"]
+        snapshot.capture(static_origin(), variants=variants)["snapshot"]
     )
     reordered = snapshot.summarize(
-        snapshot.capture(STATIC_ORIGIN, variants=variants,
+        snapshot.capture(static_origin(), variants=variants,
                          swap_rule=CONFLICTING_SELECTOR)["snapshot"]
     )