A code-declared node's shim names only its triggering ports, so a non-triggering input with no value yet reaches the function as its own default instead of failing the call

backend/fluksio/sdk/__init__.py

@@ -877,12 +877,16 @@ def _shim(spec: NodeSpec) -> str:
     The import is aliased because ``process``'s parameters are the node's port
     names, and a port may be named after the very function it feeds — which
     would otherwise shadow the import inside the body.
+
+    Only the triggering ports are named. The engine leaves out an input that
+    has no value yet, which only a port that does not trigger can lack, so
+    those travel in ``**settings`` and the function's own default applies.
     """
     _refuse_main(spec)
     fn = spec.fn
     where = inspect.getsourcefile(fn) or fn.__module__
     repo = import_root(fn)
-    ports = [port.port for port in spec.requires]
+    ports = [port.port for port in spec.requires if port.trigger]
     signature = ", ".join(ports + ["**settings"])
     arguments = ", ".join([f"{port}={port}" for port in ports] + ["**settings"])
     call = f"_impl({arguments})"

backend/tests/sdk/test_build.py

@@ -240,6 +240,28 @@ def test_a_port_named_like_its_function_still_calls_the_function():
     assert namespace["process"](scale=2.0) == {"scaled": 4.0}
 
 
+@node(
+    requires=["value", Port("factor", "float", trigger=False)],
+    provides=Port("scaled", "float"),
+)
+def scale_by(value, factor=3.0):
+    return value * factor
+
+
+def test_a_port_that_does_not_trigger_may_be_missing_from_the_call():
+    """The engine leaves out an input with no value yet, so the default applies."""
+    flow = Flow(
+        "optional",
+        nodes=[scale_by],
+        inputs=[Port("value", "float", initial=1.0), Port("factor", "float")],
+    )
+    namespace: dict = {}
+    exec(compile(flow.shims()["scale_by"], "<shim>", "exec"), namespace)
+
+    assert namespace["process"](value=2.0) == {"scaled": 6.0}
+    assert namespace["process"](value=2.0, factor=0.5) == {"scaled": 1.0}
+
+
 def reads_settings(settings):
     return settings