diff --git a/internal/tools/delegate.go b/internal/tools/delegate.go
index ecc5c460..2bfca7f4 100644
--- a/internal/tools/delegate.go
+++ b/internal/tools/delegate.go
@@ -51,6 +51,13 @@ type DelegationTask struct {
 	progressEnabled bool               `json:"-"` // resolved from team settings or global default
 }
 
+// originKey returns a composite key scoping this delegation to its origin conversation.
+// Used for sibling counting and artifact accumulation so that delegations from
+// different channels/chats are NOT treated as siblings of each other.
+func (t *DelegationTask) originKey() string {
+	return t.SourceAgentID.String() + ":" + t.OriginChannel + ":" + t.OriginChatID
+}
+
 // DelegateOpts configures a single delegation call.
 type DelegateOpts struct {
 	TargetAgentKey    string
diff --git a/internal/tools/delegate_async.go b/internal/tools/delegate_async.go
index 48ed8106..2f4c4ca7 100644
--- a/internal/tools/delegate_async.go
+++ b/internal/tools/delegate_async.go
@@ -68,8 +68,11 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 		close(progressDone)
 		duration := time.Since(startTime)
 
-		// Count sibling delegations still running (exclude self)
-		siblings := dm.ListActive(task.SourceAgentID)
+		// Count sibling delegations still running (exclude self).
+		// Scoped by origin (channel + chatID) so delegations from different
+		// conversations are NOT treated as siblings of each other.
+		oKey := task.originKey()
+		siblings := dm.ListActiveForOrigin(oKey)
 		siblingCount := 0
 		for _, s := range siblings {
 			if s.ID != task.ID {
@@ -104,7 +107,7 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 				if task.TeamTaskID != uuid.Nil {
 					arts.CompletedTaskIDs = []string{task.TeamTaskID.String()}
 				}
-				dm.accumulateArtifacts(task.SourceAgentID, arts)
+				dm.accumulateArtifacts(oKey, arts)
 
 				// Emit accumulated event so WS clients know this delegation finished
 				// but results are being held until siblings complete.
@@ -134,7 +137,7 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 				dm.progressSent.Delete(task.SourceAgentID.String() + ":" + task.OriginChatID)
 
 				// Last completion: collect all accumulated artifacts + own result
-				artifacts := dm.collectArtifacts(task.SourceAgentID)
+				artifacts := dm.collectArtifacts(oKey)
 				if result != nil {
 					artifacts.Media = append(artifacts.Media, result.MediaPaths...)
 					artifacts.Results = append(artifacts.Results, DelegateResultSummary{
diff --git a/internal/tools/delegate_state.go b/internal/tools/delegate_state.go
index 9ce83b85..7942405e 100644
--- a/internal/tools/delegate_state.go
+++ b/internal/tools/delegate_state.go
@@ -93,6 +93,21 @@ func (dm *DelegateManager) ListActive(sourceAgentID uuid.UUID) []*DelegationTask
 	return tasks
 }
 
+// ListActiveForOrigin returns active delegations scoped to the same origin conversation.
+// Only delegations matching the same source agent + channel + chatID are returned.
+// This prevents cross-session sibling counting when multiple chats delegate concurrently.
+func (dm *DelegateManager) ListActiveForOrigin(originKey string) []*DelegationTask {
+	var tasks []*DelegationTask
+	dm.active.Range(func(_, val any) bool {
+		t := val.(*DelegationTask)
+		if t.originKey() == originKey && t.Status == "running" {
+			tasks = append(tasks, t)
+		}
+		return true
+	})
+	return tasks
+}
+
 // ActiveCountForLink counts running delegations for a specific source→target pair.
 func (dm *DelegateManager) ActiveCountForLink(sourceID, targetID uuid.UUID) int {
 	count := 0
@@ -119,11 +134,11 @@ func (dm *DelegateManager) ActiveCountForTarget(targetID uuid.UUID) int {
 	return count
 }
 
-// accumulateArtifacts merges new artifacts into the pending set for a source agent.
+// accumulateArtifacts merges new artifacts into the pending set for an origin conversation.
 // Called for intermediate delegation completions (when siblings are still running).
-func (dm *DelegateManager) accumulateArtifacts(sourceAgentID uuid.UUID, arts *DelegateArtifacts) {
-	key := sourceAgentID.String()
-	existing, _ := dm.pendingArtifacts.Load(key)
+// The originKey scopes accumulation to the same source agent + channel + chatID.
+func (dm *DelegateManager) accumulateArtifacts(originKey string, arts *DelegateArtifacts) {
+	existing, _ := dm.pendingArtifacts.Load(originKey)
 	var merged DelegateArtifacts
 	if existing != nil {
 		merged = *existing.(*DelegateArtifacts)
@@ -131,14 +146,13 @@ func (dm *DelegateManager) accumulateArtifacts(sourceAgentID uuid.UUID, arts *De
 	merged.Media = append(merged.Media, arts.Media...)
 	merged.Results = append(merged.Results, arts.Results...)
 	merged.CompletedTaskIDs = append(merged.CompletedTaskIDs, arts.CompletedTaskIDs...)
-	dm.pendingArtifacts.Store(key, &merged)
+	dm.pendingArtifacts.Store(originKey, &merged)
 }
 
-// collectArtifacts retrieves and removes all accumulated artifacts for a source agent.
+// collectArtifacts retrieves and removes all accumulated artifacts for an origin conversation.
 // Called when the last delegation completes (siblingCount == 0).
-func (dm *DelegateManager) collectArtifacts(sourceAgentID uuid.UUID) *DelegateArtifacts {
-	key := sourceAgentID.String()
-	if pending, ok := dm.pendingArtifacts.LoadAndDelete(key); ok {
+func (dm *DelegateManager) collectArtifacts(originKey string) *DelegateArtifacts {
+	if pending, ok := dm.pendingArtifacts.LoadAndDelete(originKey); ok {
 		return pending.(*DelegateArtifacts)
 	}
 	return &DelegateArtifacts{}