diff --git a/internal/agent/resolver_helpers.go b/internal/agent/resolver_helpers.go
index b394b1c2..057da8ef 100644
--- a/internal/agent/resolver_helpers.go
+++ b/internal/agent/resolver_helpers.go
@@ -142,18 +142,24 @@ func buildTeamMD(team *store.TeamData, members []store.TeamMemberData, selfID uu
 		}
 	}
 
-	// Workflow guidance
+	// Workflow guidance — version-aware to match backend behavior.
+	// V2: spawn auto-creates tasks, leads should NOT manually create.
+	// V1: leads must create tasks first, then spawn with team_task_id.
 	sb.WriteString("\n## Workflow\n\n")
 	if selfRole == store.TeamRoleLead {
-		sb.WriteString("**ONE delegation = ONE spawn call.** System auto-creates a tracking task per delegation.\n")
-		sb.WriteString("The `label` parameter sets the task title (keep it short). Tasks auto-complete when delegation finishes.\n\n")
-		sb.WriteString("Rules:\n")
-		sb.WriteString("- Call all spawns first, then briefly tell the user what you delegated\n")
-		sb.WriteString("- Do NOT add confirmations (\"Done!\", \"Got it!\") — just state what was assigned\n")
-		sb.WriteString("- Parallel results arrive in a single combined notification — do NOT present partial results\n")
-		sb.WriteString("- For dependency chains: `team_tasks` create with blocked_by, then `spawn` with team_task_id\n")
-
 		if isV2 {
+			sb.WriteString("**NEVER use `team_tasks create` before spawning.** The system handles task creation automatically.\n\n")
+			sb.WriteString("WRONG: `team_tasks(action=\"create\", ...)` → `spawn(team_task_id=...)`\n")
+			sb.WriteString("CORRECT: `spawn(agent=\"...\", task=\"...\", label=\"short title\")`\n\n")
+			sb.WriteString("Just call `spawn` — the system auto-creates one tracking task per delegation.\n")
+			sb.WriteString("The `label` parameter sets the auto-created task title. Tasks auto-complete when delegation finishes.\n\n")
+			sb.WriteString("Rules:\n")
+			sb.WriteString("- Each spawn call creates its own task — never pass the same `team_task_id` to multiple spawns\n")
+			sb.WriteString("- Call all spawns first, then briefly tell the user what you delegated\n")
+			sb.WriteString("- Do NOT add confirmations (\"Done!\", \"Got it!\") — just state what was assigned\n")
+			sb.WriteString("- Parallel results arrive in a single combined notification — do NOT present partial results\n")
+			sb.WriteString("- `team_tasks create` is ONLY for dependency chains (tasks with `blocked_by`), then `spawn` with that `team_task_id`\n")
+
 			sb.WriteString("\n## Orchestration Patterns\n\n")
 			sb.WriteString("- **Sequential**: A finishes → review → delegate to B with A's output\n")
 			sb.WriteString("- **Iterative**: A drafts → B reviews → A revises with feedback\n")
@@ -164,6 +170,14 @@ func buildTeamMD(team *store.TeamData, members []store.TeamMemberData, selfID uu
 			sb.WriteString("\n## Follow-up Reminders\n\n")
 			sb.WriteString("When waiting for user reply: create+claim task, then `await_reply` with text=<reminder>.\n")
 			sb.WriteString("System auto-sends reminders. Call `clear_followup` when user replies.\n")
+		} else {
+			sb.WriteString("Create a task with `team_tasks` first, then `spawn` with that `team_task_id`.\n")
+			sb.WriteString("Tasks auto-complete when delegation finishes.\n\n")
+			sb.WriteString("Rules:\n")
+			sb.WriteString("- Each task should have exactly one spawn (1:1 mapping)\n")
+			sb.WriteString("- Call all spawns first, then briefly tell the user what you delegated\n")
+			sb.WriteString("- Do NOT add confirmations (\"Done!\", \"Got it!\") — just state what was assigned\n")
+			sb.WriteString("- Parallel results arrive in a single combined notification — do NOT present partial results\n")
 		}
 
 		sb.WriteString("\nFor simple questions about team composition, answer directly from the member list above.\n")
diff --git a/internal/agent/systemprompt.go b/internal/agent/systemprompt.go
index 36ac3190..c5f1dbc0 100644
--- a/internal/agent/systemprompt.go
+++ b/internal/agent/systemprompt.go
@@ -85,7 +85,7 @@ var coreToolSummaries = map[string]string{
 	"handoff":                 "Transfer conversation to another agent (ONLY when user explicitly asks to switch agents — NOT for task delegation)",
 	"evaluate_loop":           "Run a generate→evaluate→revise loop between two agents for quality-critical tasks",
 	"delegate_search":         "Search for agents by expertise to find the right delegation target",
-	"team_tasks":              "Manage team task board (list, create, complete, cancel tasks)",
+	"team_tasks":              "Team task board — track progress, manage dependencies (spawn auto-creates delegation tasks)",
 	"team_message":            "Send messages to teammates (progress updates, questions)",
 	"workspace_write":         "Write files to the team shared workspace (visible to all team members)",
 	"workspace_read":          "Read, list, delete, pin, tag files in the team shared workspace",
diff --git a/internal/tools/delegate_prep.go b/internal/tools/delegate_prep.go
index 1540e231..40d415a8 100644
--- a/internal/tools/delegate_prep.go
+++ b/internal/tools/delegate_prep.go
@@ -116,6 +116,18 @@ func (dm *DelegateManager) prepareDelegation(ctx context.Context, opts DelegateO
 				opts.TeamTaskID, teamTask.Status, ownerLabel)
 		}
 
+		// Guard: reject in-progress tasks — prevent multiple delegations on the same task.
+		// This catches the pattern where an LLM reuses a team_task_id across parallel spawns.
+		if teamTask.Status == store.TeamTaskStatusInProgress {
+			ownerLabel := "another delegation"
+			if teamTask.OwnerAgentKey != "" {
+				ownerLabel = teamTask.OwnerAgentKey
+			}
+			return nil, nil, fmt.Errorf(
+				"team_task_id %s is already in progress (claimed by %q). Each spawn needs its own task — omit team_task_id to auto-create.",
+				opts.TeamTaskID, ownerLabel)
+		}
+
 		if team != nil {
 			if teamTask.TeamID != team.ID {
 				return nil, nil, fmt.Errorf("team_task_id does not belong to your team")
@@ -141,7 +153,10 @@ func (dm *DelegateManager) prepareDelegation(ctx context.Context, opts DelegateO
 		// tasks that are already running. The ClaimTask in autoCompleteTeamTask()
 		// will harmlessly fail (WHERE status='pending' won't match).
 		if team != nil && IsTeamV2(team) {
-			_ = dm.teamStore.ClaimTask(ctx, opts.TeamTaskID, targetAgent.ID, teamTask.TeamID)
+			if err := dm.teamStore.ClaimTask(ctx, opts.TeamTaskID, targetAgent.ID, teamTask.TeamID); err != nil {
+				slog.Warn("delegate: task claim race — another delegation may have claimed this task",
+					"task_id", opts.TeamTaskID, "target", opts.TargetAgentKey, "error", err)
+			}
 		}
 	}
 
diff --git a/internal/tools/subagent_spawn_tool.go b/internal/tools/subagent_spawn_tool.go
index 7af5924d..99fb9164 100644
--- a/internal/tools/subagent_spawn_tool.go
+++ b/internal/tools/subagent_spawn_tool.go
@@ -90,7 +90,7 @@ func (t *SpawnTool) Parameters() map[string]any {
 		}
 		props["team_task_id"] = map[string]any{
 			"type":        "string",
-			"description": "Team task ID to auto-complete when task finishes (for team workflows)",
+			"description": "Omit to auto-create a task (recommended). Only set for dependency chains with blocked_by tasks.",
 		}
 		props["estimated_duration"] = map[string]any{
 			"type":        "number",