diff --git a/docs/products.md b/docs/products.md
index 002ce50..d9c5158 100644
--- a/docs/products.md
+++ b/docs/products.md
@@ -30,7 +30,7 @@ object that a reached object references and no census holds is listed as `missin
 |---|---|
 | inputs | `objects`: the object table of what it reaches (`nnnotes.objects/1`); the stage's own inputs (master tables, data its parameters name) |
 | depends | `link.addresses` (when it has keys or resource paths), the `unity.export` and `sprite.crop` tasks whose results it read |
-| artifacts | `<task id>#<path>`: the product's own files; `<task id>#objects`: the object table of the objects its files use (the whole table unless the stage narrows it) |
+| artifacts | `<task id>#<path>`: the product's own files; `<task id>#objects`: the object table of the objects its files use (the whole table unless the stage narrows it to some objects, or to some files of an object: a shader's programs for one graphics API) |
 | item | one for the subject: `exported`, or `unsupported` with a reason code |
 
 The key holds the object table, so a product is assembled again exactly when a file of an object it reaches
diff --git a/src/nnnotes/pipeline/assemble.py b/src/nnnotes/pipeline/assemble.py
index 4fc3020..a1ab4e7 100644
--- a/src/nnnotes/pipeline/assemble.py
+++ b/src/nnnotes/pipeline/assemble.py
@@ -204,11 +204,35 @@ def json(self, oid: str, role: str = "json"):
 
 @dataclass
 class Assembly:
-    """What `assemble` makes: the product's files {path: (bytes, extension, kind)} and the object ids its files use
-    (None: every object of the table)."""
+    """What `assemble` makes: the product's files {path: (bytes, extension, kind)} and what of the object table they
+    use: `objects` the object ids (None: every object of the table), `roles` {object id: the roles of its files the
+    product keeps} for an object of which it uses some files only (a shader's programs for one graphics API). The
+    product's object table, and so its manifest, holds only those."""
 
     files: dict
     objects: set | None = None
+    roles: dict = field(default_factory=dict)
+
+
+def _prune(tid: str, objects: dict, made: Assembly) -> dict:
+    """The entries of an object table an Assembly keeps."""
+    keep = set(objects) if made.objects is None else set(made.objects)
+    unknown = sorted((keep | set(made.roles)) - set(objects))
+    if unknown:
+        raise ValueError(f"{tid}: objects not in the table: {', '.join(unknown[:5])}")
+    out = {}
+    for o, e in objects.items():
+        if o not in keep:
+            continue
+        roles = made.roles.get(o)
+        if roles is not None:
+            files = e.get("files") or {}
+            lacking = sorted(set(roles) - set(files))
+            if lacking:
+                raise ValueError(f"{tid}: object {o} has no {', '.join(lacking)} file")
+            e = dict(e, files={r: f for r, f in files.items() if r in roles})
+        out[o] = e
+    return out
 
 
 class ProductStage(Stage):
@@ -303,11 +327,8 @@ def run(self, task, depot) -> Output:
                 raise ValueError(f"{task.id}: a product file cannot be named {PRODUCT_TABLE!r}")
             aid = contract.artifact_id(task.id, path)
             arts.append(contract.artifact(aid, depot.add(body, ext), prov, {"kind": kind}))
-        if made.objects is not None:
-            unknown = sorted(set(made.objects) - set(doc["objects"]))
-            if unknown:
-                raise ValueError(f"{task.id}: objects not in the table: {', '.join(unknown[:5])}")
-            doc = dict(doc, objects={o: e for o, e in doc["objects"].items() if o in made.objects})
+        if made.objects is not None or made.roles:
+            doc = dict(doc, objects=_prune(task.id, doc["objects"], made))
             data = contract.encode(doc)
         aid = contract.artifact_id(task.id, PRODUCT_TABLE)
         arts.append(contract.artifact(aid, depot.add(data, "json"), prov, {"kind": TABLE_KIND}))
diff --git a/tests/pipeline/test_assemble.py b/tests/pipeline/test_assemble.py
index b14dc93..4cd733d 100644
--- a/tests/pipeline/test_assemble.py
+++ b/tests/pipeline/test_assemble.py
@@ -313,6 +313,41 @@ def assemble(self, task, objects):
         execute(t, depot, registry(Wrong({"m/a": "key/a"})), force=True)
 
 
+class Roles(Toy):
+    """A Toy that keeps the `json` file alone of the texture its prefab references."""
+
+    ROLES: dict = {oid(10): {"json"}}
+
+    def assemble(self, task, objects):
+        made = super().assemble(task, objects)
+        return assemble.Assembly(made.files, roles=self.ROLES)
+
+
+def test_a_product_keeps_some_files_of_an_object(tmp_path):
+    depot = Depot(tmp_path / "s")
+    env = env_for(depot, {"key/a": [oid(60)]})
+    exported(depot, env)
+    t, doc = product(depot, env, "m/a", {"m/a": "key/a"}, stage=Roles({"m/a": "key/a"}))
+    table = table_of(depot, doc)
+    assert set(table["objects"][oid(10)]["files"]) == {"json"}  # no image
+    assert oid(60) in table["objects"] and oid(61) in table["objects"]  # the others whole
+    entries, manifest = manifest_of(depot, t, doc)
+    assert set(manifest["objects"][oid(10)]["files"]) == {"json"}
+    assert f"{oid(10)}#image" not in {e["id"] for e in entries}
+
+
+def test_a_product_cannot_keep_a_file_an_object_lacks(tmp_path):
+    class Wrong(Roles):
+        ROLES = {oid(10): {"json", "mesh"}}
+
+    depot = Depot(tmp_path / "s")
+    env = env_for(depot, {"key/a": [oid(60)]})
+    exported(depot, env)
+    t = describe(Wrong({"m/a": "key/a"}), "m/a", None, env)
+    with pytest.raises(ValueError, match="has no mesh file"):
+        execute(t, depot, registry(Wrong({"m/a": "key/a"})), force=True)
+
+
 # ---------------------------------------------------------------- the layout
 def manifest_of(depot, t, doc):
     """(entries, the manifest) of a product layout for one result."""