feat(ledger): the consumer map surfaces — every css row carries used_by on list_shapes, flag="unused-css" (the map's negative space, surfaced never deleted), derive groups and the write-path family carry consumers, the derive line says "used by N template(s)", coverage payload unused_css + the standing block; docs, SKILL, plugin 0.1.44; the two step-2 tests expected 5 edges where fan-out makes 6 (milestone 302 step 3, #2936)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_pattern_coverage.py

@@ -604,6 +604,17 @@ def test_coverage_line_names_the_proposers_standing():
     assert "; 90 unclassified (40 proposed, 2 derive groups), largest: src" in line
     line = coverage_line({**base, "proposed": 0, "derive_groups": [{"group": "a"}]})
     assert "(1 derive group)" in line
+    # Milestone 302: a css top copy says what renders it; unused classes
+    # join the standing block only when measured (None = no evidence).
+    line = coverage_line({**base, "unclassified": 0, "proposed": 0, "derive_groups": [
+        {"group": "name:css:error-msg", "label": ".error-msg", "files": 6,
+         "consumers": {"count": 6, "paths": ["a.vue"]}}], "unused_css": 3})
+    assert "top copy .error-msg ×6 files · used by 6 templates" in line
+    assert "3 unused classes" in line
+    line = coverage_line({**base, "unclassified": 0, "proposed": 0, "derive_groups": [
+        {"group": "name:css:x", "label": ".x", "files": 2,
+         "consumers": {"count": 1, "paths": ["a.vue"]}}], "unused_css": None})
+    assert "top copy .x ×2 files · used by 1 template" in line and "unused" not in line
     # #2874: the next action on the line — biggest canon queue, widest copy.
     line = coverage_line({
         **base, "proposed": 40, "top_canon": {"snippet_id": 2844, "count": 78},