Let a port be named after the function it feeds

The generated node body imported the function under its own name and then
gave `process` the ports as parameters, so a port named like its function
shadowed the import and the call became a value calling itself —
`TypeError: 'str' object is not callable`, with the downstream node's
missing arguments as the knock-on. The import is aliased now.

Only the two names the body needs itself, `settings` and `_impl`, are
refused at sync. Every shim's text moves once, so the next sync reports
every code-defined node updated and each cached node misses a single time.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TXQv6KNyyvY7Z1etYTUUAd

backend/tests/sdk/test_build.py

@@ -187,15 +187,15 @@ def test_shim_imports_rather_than_copies():
     shims = a_flow().shims()
 
     assert shims["prepare"].startswith(MARKER)
-    assert "from tests.sdk.test_build import prepare" in shims["prepare"]
+    assert "from tests.sdk.test_build import prepare as _impl" in shims["prepare"]
     assert "def process(**settings):" in shims["prepare"]
-    assert "return prepare(**settings)" in shims["prepare"]
+    assert "return _impl(**settings)" in shims["prepare"]
 
 
 def test_shim_of_a_generator_delegates_and_keeps_its_return_value():
     """A bare `yield from` streams but drops what the generator returns."""
     assert (
-        "return (yield from fit(dataset=dataset, lr=lr, **settings))"
+        "return (yield from _impl(dataset=dataset, lr=lr, **settings))"
         in a_flow().shims()["fit"]
     )
 
@@ -221,7 +221,31 @@ def test_a_generator_shim_publishes_both_the_stream_and_the_result():
 
 
 def test_shim_of_a_single_port_wraps_the_bare_return():
-    assert "return {'score': evaluate(weights=weights" in a_flow().shims()["evaluate"]
+    assert "return {'score': _impl(weights=weights" in a_flow().shims()["evaluate"]
+
+
+@node(requires=["scale"], provides=Port("scaled", "float"))
+def scale(scale):
+    return scale * 2.0
+
+
+def test_a_port_named_like_its_function_still_calls_the_function():
+    """The body imports under an alias, so the port cannot shadow the function."""
+    flow = Flow("collide", nodes=[scale], inputs=[Port("scale", "float", initial=1.0)])
+    namespace: dict = {}
+    exec(compile(flow.shims()["scale"], "<shim>", "exec"), namespace)
+
+    assert namespace["process"](scale=2.0) == {"scaled": 4.0}
+
+
+def reads_settings(settings):
+    return settings
+
+
+def test_a_port_the_generated_body_reserves_is_refused():
+    refused = node(requires=["settings"], provides=Port("out", "float"))(reads_settings)
+    with pytest.raises(SyncError, match="keeps for itself"):
+        Flow("reserved", nodes=[refused], inputs=[Port("settings", "float")])
 
 
 def test_every_shim_compiles_and_defines_process():