fix(submitqueue): keep internal merge stage topic distinct from runway merge queue

platform/consumer/registry.go

@@ -62,7 +62,10 @@ type topicGroup struct {
 }
 
 // NewTopicRegistry creates a new TopicRegistry from a list of TopicConfigs.
-// Returns an error if any topic name is invalid.
+// Returns an error if any topic name is invalid, or if two configs share a
+// topic key — a duplicate key would silently shadow the earlier entry (last
+// write wins on the key→queue/name maps), routing publishes and subscriptions
+// registered against one topic onto another.
 func NewTopicRegistry(configs []TopicConfig) (TopicRegistry, error) {
 	queues := make(map[TopicKey]extqueue.Queue, len(configs))
 	topicNames := make(map[TopicKey]string, len(configs))
@@ -73,6 +76,12 @@ func NewTopicRegistry(configs []TopicConfig) (TopicRegistry, error) {
 			return TopicRegistry{}, fmt.Errorf("invalid topic name for key %s: %w", cfg.Key, err)
 		}
 
+		if existing, ok := topicNames[cfg.Key]; ok {
+			return TopicRegistry{}, fmt.Errorf(
+				"duplicate topic key %s: already registered with name %q, cannot also register name %q",
+				cfg.Key, existing, cfg.Name)
+		}
+
 		queues[cfg.Key] = cfg.Queue
 		topicNames[cfg.Key] = cfg.Name
 

service/submitqueue/orchestrator/server/main.go

@@ -382,7 +382,12 @@ func newTopicRegistry(q extqueue.Queue, subscriberName string) (consumer.TopicRe
 		{topickey.TopicKeySpeculate, "speculate", "orchestrator-speculate"},
 		{topickey.TopicKeyBuild, "build", "orchestrator-build"},
 		{topickey.TopicKeyBuildSignal, "buildsignal", "orchestrator-buildsignal"},
-		{topickey.TopicKeyMerge, "merge", "orchestrator-merge"},
+		// The internal merge stage is deliberately distinct from the
+		// runway-owned "merge" queue registered below — both in key (see
+		// topickey.TopicKeyMerge) and in wire name. Both topics live in the
+		// same registry over the same queue backend, so a shared key would
+		// shadow one entry and a shared name would interleave their payloads.
+		{topickey.TopicKeyMerge, "mergebatch", "orchestrator-merge"},
 		{runwaymq.TopicKeyMergeSignal, "merge-signal", "orchestrator-mergesignal"},
 		{topickey.TopicKeyConclude, "conclude", "orchestrator-conclude"},
 	}

submitqueue/core/topickey/topickey.go

@@ -42,7 +42,11 @@ const (
 	// PublishAfter when the build has not yet reached a terminal state.
 	TopicKeyBuildSignal TopicKey = "buildsignal"
 	// TopicKeyMerge is the pipeline stage where speculated batches are published for merging.
-	TopicKeyMerge TopicKey = "merge"
+	// The key value is deliberately NOT "merge": the orchestrator registers this internal
+	// stage alongside the runway-owned merge queue (runwaymq.TopicKeyMerge == "merge") in
+	// one registry over one queue backend, so both the key and the wire name must differ
+	// from runway's or the two topics collapse into each other.
+	TopicKeyMerge TopicKey = "mergebatch"
 	// TopicKeyConclude is the pipeline stage where merged requests are published for conclusion.
 	TopicKeyConclude TopicKey = "conclude"
 	// TopicKeyLog is the pipeline stage where per-request logs are written.

submitqueue/orchestrator/controller/dlq/batch_test.go

@@ -34,8 +34,8 @@ func TestDLQBatchController_InterfaceAndAccessors(t *testing.T) {
 
 	c := NewDLQBatchController(zaptest.NewLogger(t).Sugar(), testScope(), store, TopicKey(topickey.TopicKeyMerge), "orchestrator-merge-dlq")
 
-	assert.Equal(t, "merge_dlq", c.Name())
-	assert.Equal(t, consumer.TopicKey("merge_dlq"), c.TopicKey())
+	assert.Equal(t, "mergebatch_dlq", c.Name())
+	assert.Equal(t, consumer.TopicKey("mergebatch_dlq"), c.TopicKey())
 	assert.Equal(t, "orchestrator-merge-dlq", c.ConsumerGroup())
 }