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>

reuse_surface/federation.py

@@ -183,6 +183,26 @@ def resolve_source_index_path(
     return _write_remote_cache(source["repo"], url, content, cache_dir), warnings
 
 
+SCOPE_BLOCK_KEYS = {"type", "title", "description", "keywords"}
+
+
+def _shape_hint(item: dict[str, Any]) -> str:
+    """Name the likely mistake when an index row has no id.
+
+    The fenced `capability` blocks in a repo's SCOPE.md use
+    type/title/description/keywords, which is close enough to an index row to
+    be copied into one by mistake — and then the member silently contributes
+    nothing. Say so instead of leaving the author to guess.
+    """
+    if SCOPE_BLOCK_KEYS & set(item):
+        return (
+            " — looks like a SCOPE.md capability block"
+            " (type/title/description/keywords); an index row needs"
+            " id/name/summary/vector/domain/status/owner/path"
+        )
+    return ""
+
+
 def _read_index_entries(
     index_path: Path, repo: str
 ) -> tuple[list[Any], list[str]]:
@@ -234,7 +254,10 @@ def compose_federated_index(
                 continue
             cap_id = item.get("id")
             if not cap_id:
-                warnings.append(f"{source['repo']}: capability #{position} has no id, skipped")
+                warnings.append(
+                    f"{source['repo']}: capability #{position} has no id, skipped"
+                    f"{_shape_hint(item)}"
+                )
                 continue
             if cap_id in seen_ids:
                 warnings.append(