diff --git a/codewiki/src/be/updater/graph_diff.py b/codewiki/src/be/updater/graph_diff.py
index 4b8b4a2d..4044a6b9 100644
--- a/codewiki/src/be/updater/graph_diff.py
+++ b/codewiki/src/be/updater/graph_diff.py
@@ -37,8 +37,21 @@ def normalize_body(text: str | None) -> str:
     return _WS.sub(" ", (text or "").strip())
 
 
+def documented_source(node: Node) -> str:
+    """The component's code with its doc comment in front, when the code does not already hold it.
+
+    Languages like Rust keep doc comments (`///`) above the item, outside ``source_code``. Without
+    them, a change that only documents behaviour would be invisible to the updater.
+    """
+    code = node.source_code or ""
+    doc = (node.docstring or "").strip()
+    if doc and doc not in code:
+        return f"{doc}\n{code}"
+    return code
+
+
 def body_hash(node: Node) -> str:
-    return hashlib.sha1(normalize_body(node.source_code).encode("utf-8")).hexdigest()
+    return hashlib.sha1(normalize_body(documented_source(node)).encode("utf-8")).hexdigest()
 
 
 def signature(node: Node) -> dict[str, Any]:
@@ -78,8 +91,8 @@ def truncate_to_tokens(text: str, max_tokens: int) -> str:
 
 
 def unified_body_diff(old: Node | None, new: Node | None, label: str) -> str:
-    old_lines = (old.source_code or "").splitlines(keepends=True) if old else []
-    new_lines = (new.source_code or "").splitlines(keepends=True) if new else []
+    old_lines = documented_source(old).splitlines(keepends=True) if old else []
+    new_lines = documented_source(new).splitlines(keepends=True) if new else []
     diff = difflib.unified_diff(
         old_lines, new_lines, fromfile=f"a/{label}", tofile=f"b/{label}", n=2
     )
diff --git a/codewiki/src/be/updater/prompts.py b/codewiki/src/be/updater/prompts.py
index af8f044e..18dacc4b 100644
--- a/codewiki/src/be/updater/prompts.py
+++ b/codewiki/src/be/updater/prompts.py
@@ -13,7 +13,7 @@
 from codewiki.src.be.dependency_analyzer.models.core import Node
 from codewiki.src.be.prompt_template import _fence_language, _format_module_tree_str
 from codewiki.src.be.updater.change_report import LeafReport
-from codewiki.src.be.updater.graph_diff import GraphDiff
+from codewiki.src.be.updater.graph_diff import GraphDiff, documented_source
 
 VERDICT_VALUES = ("no-op", "patch", "rewrite")
 
@@ -292,7 +292,7 @@ def render_leaf_components(
         node = graph.get(cid)
         if node is None or cid not in changed or not node.source_code:
             continue
-        code = node.source_code
+        code = documented_source(node)
         if budget <= 0:
             lines.append(f"\n(code of {cid} omitted for length; use read_code_components)")
             continue
diff --git a/tests/test_updater_graph_diff.py b/tests/test_updater_graph_diff.py
index 074edc11..0f0a1c65 100644
--- a/tests/test_updater_graph_diff.py
+++ b/tests/test_updater_graph_diff.py
@@ -12,6 +12,7 @@
     CLASS_RENAMED,
     DIFF_TRUNCATED_MARKER,
     body_hash,
+    documented_source,
     diff_graphs,
 )
 from codewiki.src.be.updater.options import UpdateOptions
@@ -83,3 +84,21 @@ def test_diff_truncation():
     new = {"a.py::f": node("a.py::f", "function", big_new)}
     d = diff_graphs(old, new, UpdateOptions(max_diff_tokens=50))
     assert DIFF_TRUNCATED_MARKER in d.records["a.py::f"].diff
+
+
+def test_doc_comment_only_change_is_a_body_change():
+    # Rust keeps `///` doc comments above the item, outside source_code.
+    code = "pub fn summarize(m: &Module) -> String {\n    call(m)\n}\n"
+    a = node("src/llm.rs::summarize", "function", code)
+    b = node("src/llm.rs::summarize", "function", code)
+    b.docstring = "/// Sends only names and imports, with temperature 0 and at most 120 tokens."
+    d = diff_graphs({a.id: a}, {b.id: b})
+    assert d.body == {a.id}
+    assert "+/// Sends only names and imports, with temperature 0" in d.records[a.id].diff
+
+
+def test_docstring_inside_source_is_not_counted_twice():
+    code = 'def g():\n    """Return one."""\n    return 1\n'
+    a = node("f.py::g", "function", code)
+    a.docstring = "Return one."
+    assert documented_source(a) == code