diff --git a/backend/fluksio/api/routes/artifacts.py b/backend/fluksio/api/routes/artifacts.py
index 2667259..cea16df 100644
--- a/backend/fluksio/api/routes/artifacts.py
+++ b/backend/fluksio/api/routes/artifacts.py
@@ -217,8 +217,8 @@ def delete_artifact(
         raise HTTPException(
             status_code=409,
             detail=(
-                "The artifact is still referenced by a run, a current message or "
-                "a flow input's initial value"
+                "The artifact is still referenced by a run, a current message, "
+                "a flow input's initial value or a node setting"
             ),
         )
     if not store.delete(digest):
diff --git a/backend/fluksio/flow/runs.py b/backend/fluksio/flow/runs.py
index 698080e..50fb47f 100644
--- a/backend/fluksio/flow/runs.py
+++ b/backend/fluksio/flow/runs.py
@@ -357,11 +357,20 @@ _REF_DEPTH = 8
 _SWEEP_BATCH = 500
 
 
-def _references_in(value: Any, found: set[str], depth: int = 0) -> None:
-    """Every artifact digest inside one stored value."""
+def _references_in(
+    value: Any, found: set[str], depth: int = 0, bare: bool = False
+) -> None:
+    """Every artifact digest inside one stored value.
+
+    With ``bare``, a plain ``sha256:...`` string counts as well, which is how a
+    node setting such as a Service's ``weights`` names its artifact.
+    """
     if is_reference(value):
         found.add(str(value["digest"]))
         return
+    if bare and isinstance(value, str) and valid_digest(value):
+        found.add(value)
+        return
     if depth >= _REF_DEPTH:
         return
     if isinstance(value, dict):
@@ -371,7 +380,7 @@ def _references_in(value: Any, found: set[str], depth: int = 0) -> None:
     else:
         return
     for item in items:
-        _references_in(item, found, depth + 1)
+        _references_in(item, found, depth + 1, bare)
 
 
 def sweep_artifacts(
@@ -412,9 +421,12 @@ def referenced_artifacts(
 ) -> set[str]:
     """Every artifact digest something still refers to.
 
-    Three things do: a run that recorded it, a message currently holding it,
-    and a flow input's ``initial``, published or draft, which a flow that has
-    never started holds nowhere else.
+    Four things do: a run that recorded it, a message currently holding it,
+    a flow input's ``initial``, which a flow that has never started holds
+    nowhere else, and any node setting naming it, such as a Service's
+    ``weights``. Both the published flow and its draft count, since the draft
+    is what gets published next. Older versions live only in git history and
+    do not count.
     """
     with Session(db_engine) as session:
         keep = set(session.exec(select(col(RunArtifact.digest)).distinct()).all())
@@ -428,6 +440,8 @@ def referenced_artifacts(
                     continue
                 for declared in flow.inputs:
                     _references_in(declared.initial, keep)
+                for node in flow.nodes:
+                    _references_in(node.params, keep, bare=True)
 
     keys = state.keys()
     for start in range(0, len(keys), _SWEEP_BATCH):
diff --git a/backend/tests/test_artifacts.py b/backend/tests/test_artifacts.py
index 649a2f3..2d8fd5e 100644
--- a/backend/tests/test_artifacts.py
+++ b/backend/tests/test_artifacts.py
@@ -11,7 +11,7 @@ from fluksio.core.db import engine as db_engine
 from fluksio.flow.artifacts import ArtifactStore, VolatileStore
 from fluksio.flow.messages import MessageSpec
 from fluksio.flow.runs import new_run_id, sweep_artifacts
-from fluksio.flow.schemas import FlowDef, FlowInput
+from fluksio.flow.schemas import FlowDef, FlowInput, NodeDef
 from fluksio.flow.state import MemoryState
 from fluksio.flow.store import FlowStore
 from fluksio.models import Run, RunArtifact
@@ -136,6 +136,20 @@ def test_a_sweep_keeps_what_a_flow_input_starts_with(store, tmp_path):
         assert store.path(kept["digest"]) is not None
 
 
+def test_a_sweep_keeps_what_a_node_setting_names(store, tmp_path):
+    """A Service's weights outlive the run that produced them."""
+    weights = store.put([b"weights"])
+    orphan = store.put([b"referred to by nothing"])
+
+    flows = FlowStore(tmp_path / "flows")
+    params = {"nested": [{"weights": weights["digest"]}]}
+    flows.write_flow(FlowDef(name="f", nodes=[NodeDef(id="n", params=params)]))
+
+    assert sweep_artifacts(store, MemoryState(), grace_s=0, flows=flows) == 1
+    assert store.path(orphan["digest"]) is None
+    assert store.path(weights["digest"]) is not None
+
+
 def test_a_ring_drops_the_oldest_once_it_is_full(tmp_path):
     """What makes a camera affordable: the room is fixed, not the history."""
     ring = VolatileStore(tmp_path / "ring", limit_bytes=3000)
diff --git a/docs/code/api.md b/docs/code/api.md
index 04ccedd..99c5479 100644
--- a/docs/code/api.md
+++ b/docs/code/api.md
@@ -180,9 +180,10 @@ superusers may see answers 403 to anyone else for the frames its messages
 hold, the last 8 included (see [Who may watch a camera](../interface/dashboards.md#who-may-watch-a-camera)).
 
 A superuser can remove stored bytes with `DELETE /artifacts/<digest>`. While
-a run, a current message or a flow input's initial value still references the
-digest, the call returns `409`. The hourly sweep removes unreferenced bytes
-on its own, so this is for reclaiming space sooner.
+a run, a current message, a flow input's initial value or a node setting in a
+published or draft flow still references the digest, the call returns `409`.
+The hourly sweep removes unreferenced bytes on its own, so this is for
+reclaiming space sooner.
 
 ## Dashboards and devices
 
diff --git a/docs/code/workers.md b/docs/code/workers.md
index 0aec879..9b90629 100644
--- a/docs/code/workers.md
+++ b/docs/code/workers.md
@@ -118,6 +118,8 @@ Set `--service-host` on the worker where that address is wrong.
 
 A service's `weights` setting holds an artifact digest. The worker fetches it
 as node code fetches an artifact and passes the local path as `{weights}`.
+The hourly artifact sweep keeps any digest a node setting names in a published
+or draft flow, so the weights stay after the run that produced them is deleted.
 
 ## Resources and artifacts