diff --git a/docs/changes/unreleased/2468-collections-factory-job-feature.md b/docs/changes/unreleased/2468-collections-factory-job-feature.md
new file mode 100644
index 0000000000..2be520b63e
--- /dev/null
+++ b/docs/changes/unreleased/2468-collections-factory-job-feature.md
@@ -0,0 +1,11 @@
+---
+kind: added
+title: Engines whose collections hold Factory jobs announce collections.factory_job
+pr: 2468
+surface: [app]
+invalidates: []
+---
+
+A client requires `collections.factory_job` in `hello.features` before it relies
+on adding a `factory_job` ref to a collection. An engine that announces only
+`collections` may refuse that kind with `bad_params`.
diff --git a/docs/design/app-v3/PROTOCOL.md b/docs/design/app-v3/PROTOCOL.md
index 2b746cbd82..7e9c5637b4 100644
--- a/docs/design/app-v3/PROTOCOL.md
+++ b/docs/design/app-v3/PROTOCOL.md
@@ -296,6 +296,10 @@ keeps the value in a private file the agent's commands read (the model's own
 Collection refs include `factory_job`, with a canonical positive decimal job `id`
 and a required `factory` field. The pair addresses the same job as `factory.job`.
 Other ref kinds have no `factory`. Several collections can reference the same job.
+Engines whose collections hold `factory_job` refs announce
+`collections.factory_job` in `hello.features`. A client requires it before it
+relies on adding a job: an engine that announces only `collections` may refuse
+the kind with `bad_params`.
 Factory job targets carry the recorded title, state word and repository; an
 unavailable Factory produces an `unknown` target and status. A missing job
 produces a `deleted` target. Resolution uses one bounded batch across nested
diff --git a/internal/appwire/collections_factory_job.go b/internal/appwire/collections_factory_job.go
new file mode 100644
index 0000000000..c71b0e062f
--- /dev/null
+++ b/internal/appwire/collections_factory_job.go
@@ -0,0 +1,17 @@
+package appwire
+
+// FeatureCollectionsFactoryJob names an engine whose collections hold
+// factory_job references: a Factory job by its factory and job number. A
+// client requires it before it relies on adding a job to a collection: an
+// engine that announces only "collections" may refuse the kind with bad_params.
+const FeatureCollectionsFactoryJob = "collections.factory_job"
+
+// withCollectionsFactoryJobFeature is hello carrying collections.factory_job
+// when the engine serves collections: this wire checks the factory_job kind
+// and passes it to every collector.
+func withCollectionsFactoryJobFeature(hello Hello, e Engine) Hello {
+	if _, ok := e.(Collector); !ok {
+		return hello
+	}
+	return withFeature(hello, FeatureCollectionsFactoryJob)
+}
diff --git a/internal/appwire/collections_factory_job_feature_test.go b/internal/appwire/collections_factory_job_feature_test.go
new file mode 100644
index 0000000000..24a6ee2bf2
--- /dev/null
+++ b/internal/appwire/collections_factory_job_feature_test.go
@@ -0,0 +1,38 @@
+package appwire
+
+import (
+	"slices"
+	"testing"
+)
+
+// An engine announces collections.factory_job only when it serves
+// collections, so a client can tell before it adds a job.
+func TestCollectionsFactoryJobFeatureFollowsCollections(t *testing.T) {
+	if h := withCollectionsFactoryJobFeature(Hello{}, &fakeEngine{}); len(h.Features) != 0 {
+		t.Fatalf("an engine without collections announces %v", h.Features)
+	}
+	h := withCollectionsFactoryJobFeature(Hello{}, &fakeCollector{fakeEngine: &fakeEngine{}})
+	if len(h.Features) != 1 || h.Features[0] != FeatureCollectionsFactoryJob {
+		t.Fatalf("a collector announces %v", h.Features)
+	}
+}
+
+// The announced feature is served: a factory_job ref with its factory reaches
+// the collector, and one without a factory is refused before it.
+func TestCollectionsFactoryJobFeatureIsServed(t *testing.T) {
+	w, engine := startCollectorWire(t)
+	if !slices.Contains(features(w.next()), FeatureCollectionsFactoryJob) {
+		t.Fatal("hello lacks collections.factory_job")
+	}
+	w.send(`{"id":1,"method":"collections.add","params":{"id":"c1","refs":[{"kind":"factory_job","id":"7","factory":"f"}]}}`)
+	if got := w.next(); got["error"] != nil {
+		t.Fatalf("factory_job add = %v", got)
+	}
+	if len(engine.added) != 1 || engine.added[0].Kind != RefFactoryJob || engine.added[0].ID != "7" || engine.added[0].Factory != "f" {
+		t.Fatalf("collector got %+v", engine.added)
+	}
+	w.send(`{"id":2,"method":"collections.add","params":{"id":"c1","refs":[{"kind":"factory_job","id":"7"}]}}`)
+	if got := w.next(); got["error"] == nil || got["error"].(map[string]any)["code"] != CodeBadParams {
+		t.Fatalf("factory_job without a factory = %v", got)
+	}
+}
diff --git a/internal/appwire/collections_test.go b/internal/appwire/collections_test.go
index 782a02cdae..7b06bfac33 100644
--- a/internal/appwire/collections_test.go
+++ b/internal/appwire/collections_test.go
@@ -106,12 +106,12 @@ func features(hello map[string]any) []any {
 // engine without collections answers its methods unknown_method.
 func TestCollectionsFeatureFollowsTheEngine(t *testing.T) {
 	w, _ := startCollectorWire(t)
-	if got := features(w.next()); len(got) != 3 || got[0] != "x" || got[1] != FeatureAgentEffortRungs || got[2] != FeatureCollections {
+	if got := features(w.next()); len(got) != 4 || got[0] != "x" || got[1] != FeatureAgentEffortRungs || got[2] != FeatureCollections || got[3] != FeatureCollectionsFactoryJob {
 		t.Fatalf("features = %v", got)
 	}
 	plain := startWire(t, &fakeEngine{})
 	for _, f := range features(plain.next()) {
-		if f == FeatureCollections {
+		if f == FeatureCollections || f == FeatureCollectionsFactoryJob {
 			t.Fatal("an engine without collections claims them")
 		}
 	}
diff --git a/internal/appwire/server.go b/internal/appwire/server.go
index 0e20f284df..5f4cfe85ed 100644
--- a/internal/appwire/server.go
+++ b/internal/appwire/server.go
@@ -289,6 +289,7 @@ func (s *Server) Serve(ctx context.Context, in io.Reader, hello Hello, engine En
 	hello = withFactoryFeaturesFeature(hello, engine)
 	hello = withFactoryRepoIssuesFeature(hello, engine)
 	hello = withFactoryGroupPolicyFeature(hello, engine)
+	hello = withCollectionsFactoryJobFeature(hello, engine)
 	s.Emit(EventHello, hello)
 	if warmer, ok := engine.(Warmer); ok {
 		go warmer.Warm()