A sync that changed nothing says so again

Comparing the per-node digest against an engine that does not record one is
comparing against nothing, and reporting every node as changed on every sync
for ever — which is what a client newer than its engine did, since `NodeDef`
drops fields it has never heard of. A node is named now only when both sides
carry a digest, so a no-op sync is `unchanged` again and the signal one syncs
for is back.

That silence had also been the only sign of the mismatch, so sync now names
it: one line saying the engine stored no record of what a node's code reaches,
with both versions in it and what to run. Bumped to 0.1.6 — the digest changed
the stored document's shape, and a version that does not move makes two
different engines indistinguishable, which is the thing it was made
load-bearing for a day ago.

`— draft` was printed whenever there was simply nothing to publish, which
reads as work left unfinished. It is said only when a draft is genuinely
there, and `— published` when one was.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A9Hdrmf2cwNABCnE5x9UJa

backend/tests/api/routes/test_sync.py

@@ -104,6 +104,25 @@ def test_a_node_whose_helper_moved_is_named_by_sync():
     assert _moved_code(None, document) == []
 
 
+def test_an_engine_that_records_no_digest_is_not_a_change_every_time():
+    """It drops the field on parse, so comparing against it reports for ever.
+
+    Which is what an engine older than this client does, and what a node
+    drawn on the canvas looks like — neither is a helper somebody edited.
+    """
+    from fluksio.sdk.client import _moved_code
+
+    older = {"definition": {"nodes": [{"id": "fit"}, {"id": "prepare"}]}}
+    document = {
+        "nodes": [
+            {"id": "fit", "code_digest": "ccc"},
+            {"id": "prepare", "code_digest": ""},
+        ]
+    }
+
+    assert _moved_code(older, document) == []
+
+
 def test_a_second_sync_changes_nothing_and_commits_nothing(api, flows):
     sync([flows["train"]], api, origin=ORIGIN)
     before = commits()