diff --git a/internal/tools/delegate.go b/internal/tools/delegate.go
index aa230c9a..2d3ffe7d 100644
--- a/internal/tools/delegate.go
+++ b/internal/tools/delegate.go
@@ -86,8 +86,9 @@ type DelegateRunResult struct {
 // Used to accumulate artifacts from intermediate completions until the final
 // announce fires. New artifact types (files, voice, etc.) should be added here.
 type DelegateArtifacts struct {
-	Media   []string                // file paths to forward (images, documents, audio, etc.)
-	Results []DelegateResultSummary // result summaries from completed delegations
+	Media            []string                // file paths to forward (images, documents, audio, etc.)
+	Results          []DelegateResultSummary // result summaries from completed delegations
+	CompletedTaskIDs []string                // team task IDs auto-completed by delegations (for announce context)
 }
 
 // DelegateResultSummary is a compact representation of a delegation result
@@ -180,6 +181,7 @@ func (dm *DelegateManager) Delegate(ctx context.Context, opts DelegateOpts) (*De
 		dm.active.Delete(task.ID)
 	}()
 
+	dm.injectDependencyResults(ctx, &opts)
 	message := buildDelegateMessage(opts)
 	dm.emitEvent("delegation.started", task)
 	slog.Info("delegation started", "id", task.ID, "target", opts.TargetAgentKey, "mode", "sync")
@@ -238,6 +240,7 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 		taskCtx = tracing.WithDelegateParentTraceID(taskCtx, parentTraceID)
 	}
 
+	dm.injectDependencyResults(ctx, &opts)
 	message := buildDelegateMessage(opts)
 	dm.emitEvent("delegation.started", task)
 	slog.Info("delegation started (async)", "id", task.ID, "target", opts.TargetAgentKey)
@@ -286,6 +289,9 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 						Content:  fmt.Sprintf("[failed] %s", runErr.Error()),
 					}}
 				}
+				if task.TeamTaskID != uuid.Nil {
+					arts.CompletedTaskIDs = []string{task.TeamTaskID.String()}
+				}
 				dm.accumulateArtifacts(task.SourceAgentID, arts)
 				slog.Info("delegation announce suppressed (siblings still running)",
 					"id", task.ID, "target", task.TargetAgentKey, "siblings", siblingCount)
@@ -301,6 +307,9 @@ func (dm *DelegateManager) DelegateAsync(ctx context.Context, opts DelegateOpts)
 						Deliverables: result.Deliverables,
 					})
 				}
+				if task.TeamTaskID != uuid.Nil {
+					artifacts.CompletedTaskIDs = append(artifacts.CompletedTaskIDs, task.TeamTaskID.String())
+				}
 
 				announceMeta := map[string]string{
 					"origin_channel":      task.OriginChannel,
@@ -417,13 +426,47 @@ func (dm *DelegateManager) prepareDelegation(ctx context.Context, opts DelegateO
 			}
 			return nil, nil, fmt.Errorf("team_task_id %s not found.%s", opts.TeamTaskID, hint)
 		}
+
+		// Guard: scope task to current user_id (prevent cross-group task leak).
+		// user_id is the GROUP composite ID (e.g. "group:telegram:-1003701523276"), NOT the sender.
+		// Delegate/system channels skip this check — they operate cross-context by design.
+		currentUserID := store.UserIDFromContext(ctx)
+		channel := ToolChannelFromCtx(ctx)
+		if channel != "delegate" && channel != "system" &&
+			teamTask.UserID != "" && currentUserID != "" && teamTask.UserID != currentUserID {
+			hint := ""
+			if team != nil {
+				hint = dm.pendingTasksHint(ctx, team.ID)
+			}
+			return nil, nil, fmt.Errorf(
+				"team_task_id %s belongs to a different context. "+
+					"Create a new task with team_tasks action=create.%s",
+				opts.TeamTaskID, hint)
+		}
+
+		// Guard: reject completed/cancelled tasks — enforce "one task per delegation".
+		if teamTask.Status == store.TeamTaskStatusCompleted || teamTask.Status == "cancelled" {
+			hint := ""
+			if team != nil {
+				hint = dm.pendingTasksHint(ctx, team.ID)
+			}
+			ownerLabel := "another agent"
+			if teamTask.OwnerAgentKey != "" {
+				ownerLabel = teamTask.OwnerAgentKey
+			}
+			return nil, nil, fmt.Errorf(
+				"team_task_id %s is already %s (completed by %q). "+
+					"Create a new task with team_tasks action=create for this delegation.%s",
+				opts.TeamTaskID, teamTask.Status, ownerLabel, hint)
+		}
+
 		if team != nil {
 			if teamTask.TeamID != team.ID {
 				return nil, nil, fmt.Errorf("team_task_id does not belong to your team")
 			}
 			userID := store.UserIDFromContext(ctx)
-			channel := ToolChannelFromCtx(ctx)
-			if err := checkTeamAccess(team.Settings, userID, channel); err != nil {
+			ch := ToolChannelFromCtx(ctx)
+			if err := checkTeamAccess(team.Settings, userID, ch); err != nil {
 				return nil, nil, fmt.Errorf("team access denied: %w", err)
 			}
 		}
@@ -493,6 +536,47 @@ func (dm *DelegateManager) prepareDelegation(ctx context.Context, opts DelegateO
 	return task, link, nil
 }
 
+// injectDependencyResults fetches completed dependency results for a task's
+// blocked_by prerequisites and prepends them to opts.Context. This ensures the
+// delegate agent receives prior results without needing to search for them.
+func (dm *DelegateManager) injectDependencyResults(ctx context.Context, opts *DelegateOpts) {
+	if dm.teamStore == nil || opts.TeamTaskID == uuid.Nil {
+		return
+	}
+	teamTask, err := dm.teamStore.GetTask(ctx, opts.TeamTaskID)
+	if err != nil || len(teamTask.BlockedBy) == 0 {
+		return
+	}
+
+	var depContext []string
+	for _, depID := range teamTask.BlockedBy {
+		dep, err := dm.teamStore.GetTask(ctx, depID)
+		if err != nil || dep.Result == nil || *dep.Result == "" {
+			continue
+		}
+		result := *dep.Result
+		if len(result) > 8000 {
+			result = result[:8000] + "\n[...truncated]"
+		}
+		agentLabel := dep.OwnerAgentKey
+		if agentLabel == "" {
+			agentLabel = "unknown"
+		}
+		depContext = append(depContext, fmt.Sprintf(
+			"--- Result from dependency task %q (id=%s, by %s) ---\n%s",
+			dep.Subject, dep.ID, agentLabel, result))
+	}
+
+	if len(depContext) > 0 {
+		injected := strings.Join(depContext, "\n\n")
+		if opts.Context != "" {
+			opts.Context = injected + "\n\n" + opts.Context
+		} else {
+			opts.Context = injected
+		}
+	}
+}
+
 func buildDelegateMessage(opts DelegateOpts) string {
 	if opts.Context != "" {
 		return fmt.Sprintf("[Additional Context]\n%s\n\n[Task]\n%s", opts.Context, opts.Task)
diff --git a/internal/tools/delegate_events.go b/internal/tools/delegate_events.go
index 00a76d95..8c46819d 100644
--- a/internal/tools/delegate_events.go
+++ b/internal/tools/delegate_events.go
@@ -42,6 +42,18 @@ func formatDelegateAnnounce(task *DelegationTask, artifacts *DelegateArtifacts,
 
 	msg := "[System Message] All team delegations completed.\n\n"
 
+	// List auto-completed task IDs so LLM doesn't reuse them
+	if len(artifacts.CompletedTaskIDs) > 0 {
+		msg += "Auto-completed team tasks: "
+		for i, tid := range artifacts.CompletedTaskIDs {
+			if i > 0 {
+				msg += ", "
+			}
+			msg += tid
+		}
+		msg += "\nFor follow-up delegations, create NEW tasks (do not reuse completed task IDs).\n\n"
+	}
+
 	// Render each delegation result
 	for i, r := range artifacts.Results {
 		msg += fmt.Sprintf("--- Result from %q ---\n%s\n", r.AgentKey, r.Content)
diff --git a/internal/tools/delegate_state.go b/internal/tools/delegate_state.go
index 38ccd1d9..8ea08021 100644
--- a/internal/tools/delegate_state.go
+++ b/internal/tools/delegate_state.go
@@ -81,6 +81,7 @@ 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)
 }
 
diff --git a/ui/web/src/pages/traces/trace-detail-dialog.tsx b/ui/web/src/pages/traces/trace-detail-dialog.tsx
index c885277d..386a310a 100644
--- a/ui/web/src/pages/traces/trace-detail-dialog.tsx
+++ b/ui/web/src/pages/traces/trace-detail-dialog.tsx
@@ -144,14 +144,14 @@ export function TraceDetailDialog({ traceId, onClose, getTrace, onNavigateTrace
             {trace.input_preview && (
               <div className="rounded-md border p-3">
                 <p className="mb-1 text-xs font-medium text-muted-foreground">Input</p>
-                <pre className="max-h-[40vh] overflow-y-auto whitespace-pre-wrap break-all text-sm">{trace.input_preview}</pre>
+                <pre className="max-h-[20vh] overflow-y-auto whitespace-pre-wrap break-all text-sm">{trace.input_preview}</pre>
               </div>
             )}
 
             {trace.output_preview && (
               <div className="rounded-md border p-3">
                 <p className="mb-1 text-xs font-medium text-muted-foreground">Output</p>
-                <pre className="max-h-[40vh] overflow-y-auto whitespace-pre-wrap break-all text-sm">{trace.output_preview}</pre>
+                <pre className="max-h-[20vh] overflow-y-auto whitespace-pre-wrap break-all text-sm">{trace.output_preview}</pre>
               </div>
             )}
 
@@ -245,7 +245,7 @@ function SpanTreeNode({ node, depth }: { node: SpanNode; depth: number }) {
 
         {/* Expanded detail panel */}
         {detailOpen && (
-          <div className="space-y-2 overflow-hidden border-t px-3 py-2">
+          <div className="max-h-[50vh] space-y-2 overflow-y-auto border-t px-3 py-2">
             {span.model && (
               <div className="text-xs">
                 <span className="text-muted-foreground">Model:</span> {span.provider}/{span.model}
@@ -277,7 +277,7 @@ function SpanTreeNode({ node, depth }: { node: SpanNode; depth: number }) {
             {span.input_preview && (
               <div>
                 <p className="text-xs text-muted-foreground">Input:</p>
-                <pre className="mt-1 max-h-[40vh] overflow-y-auto break-all whitespace-pre-wrap rounded bg-muted/50 p-2 text-xs">
+                <pre className="mt-1 max-h-[20vh] overflow-y-auto break-all whitespace-pre-wrap rounded bg-muted/50 p-2 text-xs">
                   {span.input_preview}
                 </pre>
               </div>
@@ -285,7 +285,7 @@ function SpanTreeNode({ node, depth }: { node: SpanNode; depth: number }) {
             {span.output_preview && (
               <div>
                 <p className="text-xs text-muted-foreground">Output:</p>
-                <pre className="mt-1 max-h-[40vh] overflow-y-auto break-all whitespace-pre-wrap rounded bg-muted/50 p-2 text-xs">
+                <pre className="mt-1 max-h-[20vh] overflow-y-auto break-all whitespace-pre-wrap rounded bg-muted/50 p-2 text-xs">
                   {span.output_preview}
                 </pre>
               </div>