fix(preprocess): verify canonical generations and cleanup

harness/tests/test_corpus_pipeline.py

@@ -431,6 +431,20 @@ def test_unchanged_documents_skip_acquire_normalize_chunk_and_embed(tmp_path):
     assert second_embedder.calls == []
 
 
+def test_unchanged_job_reuses_active_generation_without_new_directory(tmp_path):
+    source = Source([(item("one", "a"), "hello")])
+    candidate = pipeline(tmp_path, source)
+    args = dict(workspace_id="demo", workspace_root=tmp_path,
+                config_fingerprint="sha256:" + "1" * 64,
+                input_fingerprint="sha256:" + "2" * 64)
+    first = candidate.run_as_job(**args)
+    count = len(candidate.store.list_generations())
+    second = candidate.run_as_job(**args)
+    assert second.generation == first.generation
+    assert second.published is False
+    assert len(candidate.store.list_generations()) == count
+
+
 def test_removed_documents_are_marked_and_absent_from_new_manifest(tmp_path):
     one, two = item("one", "a"), item("two", "b")
     pipeline(tmp_path, Source([(one, "one"), (two, "two")])).run()