Header removals wait for the code editor to be left: autosave saves with drop=false, so follow_header adds and renames from the header but keeps a port or setting whose parameter is gone, and leaving the editor (blur or closing the panel) saves once more with removals; source saves of a flow run one at a time

backend/fluksio/api/routes/flows.py

@@ -674,7 +674,7 @@ def read_node_source(
 
 
 def _follow_header(
-    controller: FlowController, name: str, node_id: str, code: str
+    controller: FlowController, name: str, node_id: str, code: str, drop: bool
 ) -> FlowDef | None:
     """Bring a function node's ports and settings in line with its header.
 
@@ -694,7 +694,7 @@ def _follow_header(
         or definition.origin
     ):
         return None
-    followed = follow_header(node, code)
+    followed = follow_header(node, code, drop)
     if followed == node:
         return None
     definition.nodes = [followed if n.id == node_id else n for n in definition.nodes]
@@ -716,6 +716,7 @@ async def save_node_source(
     source: NodeSource,
     controller: FlowControllerDep,
     user: CurrentUser,
+    drop: bool = True,
 ) -> Any:
     """Save a node's source as an unpublished edit and report whether it loads.
 
@@ -730,7 +731,9 @@ async def save_node_source(
 
     A node with its own code takes its input ports and settings from the
     header of ``process`` (see `follow_header`), and the answer carries the
-    node when that changed it.
+    node when that changed it. ``drop=false`` is the editor's autosave, which
+    adds and renames from the header but keeps what it no longer names until
+    the editor is left.
     """
     definition = _read_flow(controller, name)
     ref = _source_ref(definition, node_id)
@@ -746,7 +749,7 @@ async def save_node_source(
             controller.store.write_node_source, name, node_id, source.code, True
         )
     followed = await run_in_threadpool(
-        _follow_header, controller, name, node_id, source.code
+        _follow_header, controller, name, node_id, source.code, drop
     )
     node_def = next((n for n in definition.nodes if n.id == node_id), None)
     device = (

backend/fluksio/flow/controller.py

@@ -1837,7 +1837,7 @@ def _signature_gap(
     )
 
 
-def follow_header(node: NodeDef, code: str) -> NodeDef:
+def follow_header(node: NodeDef, code: str, drop: bool = True) -> NodeDef:
     """The node with its input ports and settings read off ``def process(...)``.
 
     The inverse of the canvas's scaffold, which writes the input ports first,
@@ -1845,7 +1845,9 @@ def follow_header(node: NodeDef, code: str) -> NodeDef:
     keeps its kind. A new one is a setting when it has a default, which becomes
     its value, or when it follows a setting, and an input port otherwise. One
     name swapped for one other is a rename, so the port keeps its message and
-    the setting its value. A declared name the header no longer has is dropped.
+    the setting its value. A declared name the header no longer has is dropped,
+    unless ``drop`` is false: code saved while it is still being typed keeps
+    those, so a pause mid-edit does not cost a port its message.
 
     A header this cannot read for certain leaves the node as it is: a syntax
     error, no top-level ``def process``, a decorator, ``*args``, ``**kwargs``,
@@ -1907,6 +1909,13 @@ def follow_header(node: NodeDef, code: str) -> NodeDef:
             after_setting = True
         else:
             requires.append(MessageSpec(port=name))
+    if not drop:
+        kept = set(gone) - set(renamed.values())
+        # Where they were, so that typing the name back changes nothing.
+        for index, spec in enumerate(node.requires):
+            if spec.port in kept:
+                requires.insert(index, spec)
+        params |= {key: settings[key] for key in kept if key in settings}
     # Ports the header cannot name, such as a row not named yet, stay.
     requires += [spec for spec in node.requires if not written(spec.port)]
     return node.model_copy(update={"requires": requires, "params": params})

backend/tests/api/routes/test_flows.py

@@ -580,6 +580,13 @@ def test_saving_a_header_moves_the_node_ports_in_the_draft(
     assert response["version"] == saved["definition"]["version"] + 1
     logger = next(n for n in draft["definition"]["nodes"] if n["id"] == "logger")
     assert logger["params"] == {"gain": 2}
+    # The editor's autosave: a parameter typed away keeps its port for now.
+    paused = client.put(
+        f"{PREFIX}/header/nodes/logger/source?drop=false",
+        headers=superuser_token_headers,
+        json={"code": "def process(reading, gain=2):\n    return {}\n"},
+    ).json()
+    assert paused["node"] is None
 
     client.delete(f"{PREFIX}/header", headers=superuser_token_headers)
 

backend/tests/flow/test_node_settings.py

@@ -192,6 +192,21 @@ def test_a_renamed_parameter_keeps_the_message_and_a_dropped_one_goes():
     assert dropped.params == {"factor": 3}
 
 
+def test_without_drop_a_missing_parameter_stays_and_the_rest_follows():
+    node = _flow(
+        [*READING, MessageSpec(name="garden.level", port="depth")], factor=3
+    ).nodes[0]
+
+    paused = follow_header(node, "def process(depth): pass\n", drop=False)
+    renamed = follow_header(node, "def process(value, depth, factor): pass\n", False)
+    added = follow_header(node, "def process(depth, gain=2): pass\n", drop=False)
+
+    assert paused == node
+    assert renamed.requires[0] == READING[0].model_copy(update={"port": "value"})
+    assert [spec.port for spec in added.requires] == ["reading", "depth"]
+    assert added.params == {"factor": 3, "gain": 2}
+
+
 def test_a_new_parameter_after_a_setting_is_a_setting():
     node = _flow(READING, factor=3).nodes[0]