Clarify unsatisfied resource restrictions in resource docs

docs/source/resources.rst

@@ -128,6 +128,30 @@ each task will run in a separate process:
                             resources={'process': 1}) for arg in args]
 
 
+What happens if no worker can satisfy a resource restriction?
+-------------------------------------------------------------
+
+Dask clusters are dynamic: workers may join later, and those future workers may
+provide resources that are not available right now. Because of that, submitting
+a task with currently unsatisfied resource restrictions does not immediately
+raise an exception. Instead, the task remains in the scheduler's
+``no-worker`` state and waits until a suitable worker becomes available.
+
+For example, if every connected worker advertises at most ``{"GPU": 1}``, then
+submitting a task with ``resources={"GPU": 2}`` will keep the task waiting
+rather than fail immediately.
+
+If you expect the required resources to be unavailable permanently, consider one
+of the following:
+
+- call :meth:`distributed.Future.result` with ``timeout=...`` so your client
+  code does not wait forever;
+- inspect the task state in the dashboard or scheduler diagnostics to confirm it
+  is in ``no-worker``;
+- validate your cluster's available resources before submitting tasks with
+  restrictive resource requirements.
+
+
 Resources are Abstract
 ----------------------