Name the SCOPE-block mistake in compose warnings (REUSE-WP-0020-T03)

An index row with no id now says whether it looks like a SCOPE.md capability
block, instead of leaving the author to work out why their repo contributes
nothing to the federated index. That confusion is invisible without a
diagnostic: the row is valid YAML, the file parses, and the member just
silently disappears.

Swept all 61 federation sources with --refresh: evidence-binder is the only
affected member. The other ten zero-count repos are genuine empty scaffolds.

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

tests/test_federation.py

@@ -283,3 +283,33 @@ def test_malformed_source_still_listed_with_zero_count(tmp_path, monkeypatch):
     )
     remote = next(s for s in federated["sources"] if s["repo"] == "remote-repo")
     assert remote["count"] == 0
+
+
+def test_scope_shaped_row_names_the_mistake(tmp_path, monkeypatch):
+    """A SCOPE.md capability block copied into an index should say so."""
+    body = """
+version: 1
+domain: helix_forge
+capabilities:
+  - type: library
+    title: Evidence-to-target binding
+    description: Links evidence items to structured targets.
+    keywords: [evidence, binding]
+"""
+    _, warnings = _compose_with_remote_body(body, tmp_path, monkeypatch)
+    hint = next(w for w in warnings if "remote-repo" in w)
+    assert "SCOPE.md capability block" in hint
+    assert "id/name/summary" in hint
+
+
+def test_plain_missing_id_gets_no_scope_hint(tmp_path, monkeypatch):
+    body = """
+version: 1
+capabilities:
+  - name: Has a name but no id
+    summary: Something
+"""
+    _, warnings = _compose_with_remote_body(body, tmp_path, monkeypatch)
+    hint = next(w for w in warnings if "remote-repo" in w)
+    assert "has no id" in hint
+    assert "SCOPE.md" not in hint