diff --git a/docs/capabilities/compaction.md b/docs/capabilities/compaction.md
index e0baeb25..057342d5 100644
--- a/docs/capabilities/compaction.md
+++ b/docs/capabilities/compaction.md
@@ -31,8 +31,9 @@ refuses rather than replace evidence it cannot retain. See
 
 On each request, evidence from earlier questions is replaced by the evidence those
 questions actually cited. Cited text and cited page images are kept in full, grouped by
-the question that cited them, and stay citable by the same chunk ids. Every other
-earlier evidence return becomes a short receipt. The current question is untouched.
+the question that cited them, and stay citable by the same chunk ids. Evidence spanning
+more than one collection carries a `Collection:` line naming the one it came from. Every
+other earlier evidence return becomes a short receipt. The current question is untouched.
 
 Compaction rewrites the request, never the stored history, so `all_messages()` still
 holds everything the run gathered.
diff --git a/haiku_rag_slim/haiku/rag/capabilities/compaction.py b/haiku_rag_slim/haiku/rag/capabilities/compaction.py
index bd8a935b..ed171eb0 100644
--- a/haiku_rag_slim/haiku/rag/capabilities/compaction.py
+++ b/haiku_rag_slim/haiku/rag/capabilities/compaction.py
@@ -88,13 +88,21 @@ class _Entry:
     question: int
     citation: Citation
 
-    def render(self) -> str:
+    def render(self, *, include_collection: bool = False) -> str:
+        """Render an entry, optionally naming its collection."""
         title = self.citation.document_title
         uri = self.citation.document_uri
-        source = f'"{title}"' if title else uri
+        document = f'"{title}"' if title else uri
         if title and uri and uri != title:
-            source = f"{source} ({uri})"
-        return f"[{self.chunk_id}] Source: {source}\n{self.citation.content}"
+            document = f"{document} ({uri})"
+        if include_collection and self.citation.source:
+            header = (
+                f"[{self.chunk_id}]\nCollection: {self.citation.source}\n"
+                f"Source: {document}"
+            )
+        else:
+            header = f"[{self.chunk_id}] Source: {document}"
+        return f"{header}\n{self.citation.content}"
 
 
 def _eligible_entries(evidence: Sequence[DiscoveredEvidence]) -> list[_Entry]:
@@ -154,6 +162,8 @@ def build_capsule(evidence: Sequence[DiscoveredEvidence]) -> Capsule:
     lines = [CAPSULE_HEADER]
     pictures: list[RetainedPicture] = []
     seen: set[tuple[str, str, str]] = set()
+    # A capsule may combine citations from different search scopes.
+    include_collection = len({entry.citation.source for entry in entries}) > 1
     position = 0
     current_question: int | None = None
     for entry in entries:
@@ -161,7 +171,7 @@ def build_capsule(evidence: Sequence[DiscoveredEvidence]) -> Capsule:
             position += 1
             current_question = entry.question
             lines.append(group_label(position))
-        lines.append(entry.render())
+        lines.append(entry.render(include_collection=include_collection))
         for self_ref in entry.citation.picture_refs:
             # Overlapping chunks cite one figure, and a provider counts it twice.
             # Identity is owner plus document plus reference, so the same reference
diff --git a/tests/capabilities/test_evidence_capsule.py b/tests/capabilities/test_evidence_capsule.py
index c88e8b55..03217592 100644
--- a/tests/capabilities/test_evidence_capsule.py
+++ b/tests/capabilities/test_evidence_capsule.py
@@ -97,6 +97,46 @@ def test_a_retained_picture_carries_the_source_it_came_from():
     assert picture.source == "beta"
 
 
+def test_the_capsule_names_the_collection_evidence_came_from():
+    found = discovered(cited={"a": [2], "b": [2]})
+    found = replace(
+        found,
+        citations={
+            "a": replace_citation(found.citations["a"], source="papers"),
+            "b": replace_citation(found.citations["b"], source="wiki"),
+        },
+    )
+
+    lines = build_capsule([found]).text.splitlines()
+
+    def rendered(chunk_id: str) -> list[str]:
+        start = lines.index(f"[{chunk_id}]")
+        return lines[start : start + 3]
+
+    assert rendered("a") == [
+        "[a]",
+        "Collection: papers",
+        'Source: "Title a" (test://a)',
+    ]
+    assert rendered("b") == ["[b]", "Collection: wiki", 'Source: "Title b" (test://b)']
+
+
+def test_evidence_from_one_collection_does_not_name_it():
+    found = discovered(cited={"a": [2], "b": [2]})
+    found = replace(
+        found,
+        citations={
+            chunk_id: replace_citation(cited, source="papers")
+            for chunk_id, cited in found.citations.items()
+        },
+    )
+
+    lines = build_capsule([found]).text.splitlines()
+
+    assert not [line for line in lines if line.startswith("Collection:")]
+    assert '[a] Source: "Title a" (test://a)' in lines
+
+
 def test_nothing_cited_produces_no_capsule():
     capsule = build_capsule([discovered()])