fix(formatters): render backend function names in markdown diff (closes #299)

_md_diff() read `fn` from backend node entries, but _diff_backend() renames
the field to `name` on the way out, so every function name fell through to
the empty-string default. The diff reported correct counts with blank
identities: "- + `` (a.py)".

Fixed on the consumer side — commands/diff.py, dashboard and MCP already
consume `name`, so changing the producer would break them.

Tests pin the contract against real _diff_backend() output, not a
hand-written stand-in, and fail if the fix is reverted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Wolfvin

scripts/formatters/markdown.py

@@ -1155,12 +1155,13 @@ def _md_diff(data: Dict, lines: list) -> None:
         removed = be.get("removed_count", 0)
         changed = be.get("changed_count", 0)
         lines.append(f"### Backend — +{added} / -{removed} / ~{changed}")
+        # `name`, not `fn`: _diff_backend() renames the field on the way out.
         for node in be.get("added_nodes", [])[:5]:
-            lines.append(f"- + `{node.get('fn', '')}` ({node.get('file', '')})")
+            lines.append(f"- + `{node.get('name', '')}` ({node.get('file', '')})")
         for node in be.get("removed_nodes", [])[:5]:
-            lines.append(f"- - `{node.get('fn', '')}`")
+            lines.append(f"- - `{node.get('name', '')}`")
         for node in be.get("changed_nodes", [])[:5]:
-            lines.append(f"- ~ `{node.get('fn', '')}`")
+            lines.append(f"- ~ `{node.get('name', '')}`")
         if be.get("new_dead"):
             lines.append(f"- **New dead:** {len(be['new_dead'])}")
         lines.append("")

tests/test_markdown_diff.py

@@ -0,0 +1,98 @@
+"""Tests for the markdown registry-diff renderer (issue #299).
+
+_diff_backend() emits backend node entries keyed `name`, while _md_diff()
+read `fn` and silently rendered every function name as an empty string.
+These tests pin the producer/consumer contract on both sides.
+"""
+
+import os
+import sys
+import unittest
+
+SCRIPT_DIR = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "scripts")
+sys.path.insert(0, SCRIPT_DIR)
+
+from diff_engine import _diff_backend  # noqa: E402
+from formatters.markdown import to_markdown  # noqa: E402
+
+
+def _render(backend, frontend=None):
+    return to_markdown(
+        {"status": "ok", "frontend": frontend or {}, "backend": backend}, "diff"
+    )
+
+
+class TestBackendNodeNamesRendered(unittest.TestCase):
+    """Backend function names must reach the markdown output."""
+
+    def test_added_node_name_is_rendered(self):
+        out = _render({
+            "added_count": 1, "removed_count": 0, "changed_count": 0,
+            "added_nodes": [{"name": "freshFn", "file": "a.py", "status": "active"}],
+            "removed_nodes": [], "changed_nodes": [],
+        })
+        self.assertIn("freshFn", out)
+        self.assertIn("a.py", out)
+        self.assertNotIn("- + ``", out)
+
+    def test_removed_node_name_is_rendered(self):
+        out = _render({
+            "added_count": 0, "removed_count": 1, "changed_count": 0,
+            "added_nodes": [], "changed_nodes": [],
+            "removed_nodes": [{"name": "goneFn", "file": "a.py"}],
+        })
+        self.assertIn("goneFn", out)
+        self.assertNotIn("- - ``", out)
+
+    def test_changed_node_name_is_rendered(self):
+        out = _render({
+            "added_count": 0, "removed_count": 0, "changed_count": 1,
+            "added_nodes": [], "removed_nodes": [],
+            "changed_nodes": [
+                {"name": "movedFn", "file": "a.py",
+                 "ref_count": {"from": 2, "to": 1}}
+            ],
+        })
+        self.assertIn("movedFn", out)
+        self.assertNotIn("- ~ ``", out)
+
+
+class TestContractWithProducer(unittest.TestCase):
+    """Render real _diff_backend() output, not a hand-written stand-in."""
+
+    def test_real_diff_backend_output_renders_names(self):
+        old = {
+            "nodes": [{"id": "a.py:1", "fn": "goneFn", "file": "a.py",
+                       "ref_count": 1, "status": "active"}],
+            "edges": [],
+        }
+        new = {
+            "nodes": [{"id": "a.py:9", "fn": "freshFn", "file": "a.py",
+                       "ref_count": 1, "status": "active"}],
+            "edges": [],
+        }
+
+        out = _render(_diff_backend(old, new))
+
+        self.assertIn("freshFn", out)
+        self.assertIn("goneFn", out)
+
+
+class TestFrontendNotRegressed(unittest.TestCase):
+    """The frontend block already read `name` correctly — keep it that way."""
+
+    def test_frontend_class_names_still_rendered(self):
+        out = _render(
+            {},
+            frontend={
+                "added_count": 1, "removed_count": 0, "changed_count": 0,
+                "added_classes": [{"name": "btn-primary", "status": "active"}],
+                "removed_classes": [], "changed_classes": [],
+                "added_ids": [], "removed_ids": [], "changed_ids": [],
+            },
+        )
+        self.assertIn("btn-primary", out)
+
+
+if __name__ == "__main__":
+    unittest.main()