feat(schema): GREEN — rule 18, remote onprem systems must itemize product_nodes

check_deployment_rules now raises for deployment=onprem +
storage_location remote/remote_and_local when product_nodes is absent
or empty. Once the section exists, rules 2 and 6 already enforce the
per-node/per-switch power blocks, so rule 18 closes the only gap that
let a remote-storage system publish a blank Provisioned Power (W) cell.

storage_location 'local' is exempt (drives draw through client PSUs,
excluded from the power sum by definition; Chassis.rack_units ge=1 +
rule 11's total of 0 make product-side entries inexpressible), as is
cloud (power fields are forbidden there).

Verified against the live tree: fires on Everpure FBEXA + TuringData
F9200 (message names the fix), silent on FarmGPU potato + SAMSUNG
MEMORY_AE which are otherwise fully schema-valid. Surfaces through
system_yaml_schema_checks as an ERROR under the 2.1.7 mapping.

Author: FileSystemGuy

mlpstorage_py/system_description/schema_validator.py

@@ -334,8 +334,26 @@ class SystemUnderTest(StrictModel):
 
     @model_validator(mode='after')
     def check_deployment_rules(self) -> 'SystemUnderTest':
-        # Rules 1–6 (onprem) and 7–10 (cloud)
+        # Rules 1–6 + 18 (onprem) and 7–10 (cloud)
         if self.deployment == DeploymentMode.onprem:
+            # Rule 18: external storage must be itemized. The results
+            # table's Provisioned Power (W) cell derives from the power
+            # blocks on product_nodes/product_switches; a remote-storage
+            # system without a product_nodes section silently publishes a
+            # blank cell. 'local' systems are exempt — their storage draws
+            # through client PSUs (excluded from the power sum by
+            # definition) and rule 11 pins their rack-unit total to 0.
+            storage_loc = self.solution.architecture.storage_location
+            if (storage_loc in (StorageLocation.remote,
+                                StorageLocation.remote_and_local)
+                    and not self.product_nodes):
+                raise ValueError(
+                    f"product_nodes is required for onprem deployment when "
+                    f"storage_location is '{storage_loc.value}' — the "
+                    f"storage-side hardware and its power supplies must be "
+                    f"itemized (the results table's Provisioned Power (W) "
+                    f"cell is derived from them)"
+                )
             for i, node in enumerate(self.product_nodes or []):
                 if node.chassis.rack_units is None:
                     raise ValueError(f"product_nodes[{i}].chassis.rack_units is required for onprem deployment")