docs(data-designer): address Knepper review on submit-only seeds/providers

Clarify that local file/DataFrame seeds remain library-valid but not on
the platform path, and that remote validate/submit is IGW-provider-only.

Signed-off-by: Matt Kornfield <mkornfield@nvidia.com>

Author: mckornfield

docs/data-designer/tutorials/seeding.mdx

@@ -11,15 +11,16 @@ This tutorial demonstrates how to use external datasets as seed data for synthet
 
 For more detail about seed dataset behavior, see the [open-source library's version](https://docs.nvidia.com/nemo/datadesigner/v0.9.1/tutorials/seeding-with-an-external-dataset) of this tutorial.
 
-## Seed Sources by Execution Mode
+## Seed Sources on the Platform
 
-Seed source support depends on platform resource availability:
+This tutorial covers platform execution (`nemo data-designer … submit` and the SDK). Seed support there is narrower than the open-source Data Designer library:
 
-| Seed source | CLI `submit` / SDK today | Use case |
-|-------------|--------------------------|----------|
-| **Local files or DataFrames** | Not supported | Upload local files to Filesets first. |
-| **HuggingFace** | Supported | Publicly available datasets or private HuggingFace datasets. |
+| Seed source | Platform (`submit` / SDK) | Notes |
+|-------------|---------------------------|-------|
+| **Local files or DataFrames** | Not supported on the platform path | Still valid in the [open-source library](https://docs.nvidia.com/nemo/datadesigner/v0.9.1/tutorials/seeding-with-an-external-dataset). For platform jobs, upload files to a Fileset first (see Step 1 below). |
+| **HuggingFace** | Supported | Public or private HuggingFace datasets (private needs a Secrets API token). |
 | **Files API Filesets** | Supported | Shared seed data stored through the Files API. |
+
 ### HuggingFace Datasets
 
 Use `HuggingFaceSeedSource` to load data from HuggingFace:

plugins/nemo-data-designer/README.md

@@ -27,8 +27,8 @@ The exit code is `0` only when every requested context validates cleanly. JSON o
 
 ### Local vs. remote
 
-- **Local** checks library-level compatibility: the engine compiles the config and resolves model providers. Providers can be defined locally **or** referenced by name from the Inference Gateway — both are first-class.
-- **Remote** mirrors what `nemo data-designer <preview|create> submit` accepts: unsupported seed types and `tool_configs` are rejected, IGW providers are resolved against the platform, Files-service seeds are looked up, and Nemotron Personas filesets are checked. The remote pass is a client-side simulation of those checks; it does not contact the data-designer service.
+- **Local** (`--execution-context local`) checks open-source library compatibility: the engine compiles the config and resolves model providers the library understands (including locally defined providers). This is a library/config check, not a platform execution path — there is no `nemo data-designer … run` verb.
+- **Remote** (`--execution-context remote`) mirrors what `nemo data-designer <preview|create> submit` accepts on the platform: local seed types and `tool_configs` are rejected, **only Inference Gateway providers** are accepted, Files-service seeds are looked up, and Nemotron Personas filesets are checked. The remote pass is a client-side simulation of those checks; it does not contact the data-designer service.
 
 ### Programmatic use