Warn when a node that runs no code names a device

A device on a node without source was accepted and silently ignored. The
build now reports it as ignored_device, an advisory issue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx

backend/fluksio/flow/controller.py

@@ -174,6 +174,8 @@ class LoadedNode:
     #: Published, and with no body of its own — so what runs is the new-node
     #: template, which returns nothing at all.
     missing_source: bool = False
+    #: The device this node names although its type never runs on a worker.
+    ignored_device: str = ""
 
 
 @dataclass
@@ -1041,6 +1043,8 @@ class FlowController:
             node_type = NODE_TYPES.get(node_def.type)
             if node_type is None:
                 raise ValueError(f"Unknown node type '{node_def.type}'")
+            if node_def.device and not node_type.has_source:
+                entry.ignored_device = node_def.device
 
             params = resolve_params(node_def.params)
 
@@ -1923,6 +1927,22 @@ def _collect_issues(
         for entry in loaded.values()
         if entry.missing_source
     ]
+    # Only code travels to a worker, so a device on any other node is a field
+    # nothing reads. Saying so beats a setting that looks like it took.
+    issues += [
+        ValidationIssue(
+            code="ignored_device",
+            message=(
+                f"Node '{entry.id.rpartition('.')[2]}' names device "
+                f"'{entry.ignored_device}', but only a Function node runs on a "
+                "worker. The setting is ignored."
+            ),
+            flow=entry.flow,
+            node=entry.id,
+        )
+        for entry in loaded.values()
+        if entry.ignored_device
+    ]
     return issues
 
 

backend/fluksio/flow/pipeline.py

@@ -46,7 +46,7 @@ MANUAL_RUN_PREFIX = "manual-"
 # neither the brain graph nor the health summary treats them as a fault.
 # Lives here rather than beside the controller so `ValidationIssue` can carry
 # the distinction itself, and every reader gets it for free.
-ADVISORY_ISSUES = frozenset({"unauthenticated_hook"})
+ADVISORY_ISSUES = frozenset({"unauthenticated_hook", "ignored_device"})
 
 
 class ValidationIssue(BaseModel):
@@ -61,6 +61,7 @@ class ValidationIssue(BaseModel):
         "self_loop_needs_initial",
         "missing_source",
         "node_unhealthy",
+        "ignored_device",
     ]
     message: str
     flow: str = ""

backend/tests/flow/test_drafts.py

@@ -125,6 +125,29 @@ def test_a_published_node_with_no_body_is_reported(store: FlowStore):
     assert [i for i in controller.issues if i.code == "missing_source"] == []
 
 
+def test_a_device_on_a_node_without_code_is_reported(store: FlowStore):
+    """Only code travels to a worker, so the device would be ignored silently."""
+    store.write_flow(
+        FlowDef(
+            name="heating",
+            nodes=[
+                NodeDef(
+                    id="relay",
+                    type="change",
+                    device="gpu",
+                    provides=[MessageSpec(name="temp")],
+                )
+            ],
+        )
+    )
+    controller = FlowController(store)
+
+    asyncio.run(controller.reload())
+    (issue,) = [i for i in controller.issues if i.code == "ignored_device"]
+    assert issue.node == "heating.relay"
+    assert issue.advisory
+
+
 def test_a_node_being_written_in_the_editor_is_not_reported(store: FlowStore):
     """A draft legitimately has no published body yet — that is what a draft is."""
     store.write_draft(a_flow(), 0)