diff --git a/diffgraph/structural.py b/diffgraph/structural.py
index e3985ec..5c00fa3 100644
--- a/diffgraph/structural.py
+++ b/diffgraph/structural.py
@@ -739,6 +739,18 @@ def _parse_failure_warning(
     )
 
 
+def _unsupported_language_warning(entry: SnapshotEntry, path: str) -> Dict[str, str]:
+    """Record the immutable snapshots outside the deterministic baseline."""
+    return _warning(
+        "UNSUPPORTED_LANGUAGE",
+        path,
+        "Deterministic extraction currently supports Python (.py) only; "
+        "pre-change blob {}; post-change blob {}.".format(
+            entry.old_oid or "absent", entry.new_oid or "absent",
+        ),
+    )
+
+
 def _symbol_id(path: str, qualified_name: str) -> str:
     return "sym::{}::{}".format(path, qualified_name)
 
@@ -966,7 +978,7 @@ def analyze_local_diff(
             continue
         if file_entry["language"] != "python":
             skipped += 1
-            warnings.append(_warning("UNSUPPORTED_LANGUAGE", path, "Deterministic extraction currently supports Python (.py) only."))
+            warnings.append(_unsupported_language_warning(entry, path))
             continue
         if (old is None and entry.old_oid is not None) or (
             new is None and entry.new_oid is not None
diff --git a/tests/test_structural.py b/tests/test_structural.py
index 35d388b..3e5490b 100644
--- a/tests/test_structural.py
+++ b/tests/test_structural.py
@@ -181,16 +181,46 @@ def test_pathspec_scope_is_not_widened(tmp_path):
 
 
 def test_unsupported_language_is_explicit_and_not_overclaimed(tmp_path):
+    """Unsupported snapshots keep their explicit capability boundary and blobs."""
     root = repo(tmp_path)
     write(root, "main.js", "export function value() { return 1; }\n")
     commit(root)
     write(root, "main.js", "export function value() { return 2; }\n")
+    old_oid = git(root, "rev-parse", "HEAD:main.js")
+    new_oid = git(root, "hash-object", "main.js")
     artifact = analyze_local_diff(str(root))
     assert_valid(artifact)
     assert artifact["symbols"] == []
     assert artifact["metadata"]["files_skipped"] == 1
     assert artifact["metadata"]["warnings"][0]["code"] == "UNSUPPORTED_LANGUAGE"
-    assert "Python" in artifact["metadata"]["warnings"][0]["detail"]
+    assert artifact["metadata"]["warnings"][0]["detail"] == (
+        "Deterministic extraction currently supports Python (.py) only; "
+        "pre-change blob {}; post-change blob {}."
+    ).format(old_oid, new_oid)
+
+
+@pytest.mark.parametrize("change_kind", ["added", "deleted"])
+def test_unsupported_language_one_sided_blob_is_absent(tmp_path, change_kind):
+    """Added and deleted unsupported snapshots identify their missing blob side."""
+    root = repo(tmp_path)
+    write(root, "main.js", "export function value() { return 1; }\n")
+    commit(root)
+
+    if change_kind == "added":
+        write(root, "added.js", "export function value() { return 2; }\n")
+        old_oid = "absent"
+        new_oid = git(root, "hash-object", "added.js")
+    else:
+        old_oid = git(root, "rev-parse", "HEAD:main.js")
+        (root / "main.js").unlink()
+        new_oid = "absent"
+
+    artifact = analyze_local_diff(str(root))
+    assert_valid(artifact)
+    assert artifact["metadata"]["warnings"][0]["detail"] == (
+        "Deterministic extraction currently supports Python (.py) only; "
+        "pre-change blob {}; post-change blob {}."
+    ).format(old_oid, new_oid)
 
 
 @pytest.mark.parametrize("staged", [False, True])