fix(orch): improve spawn/subagent tool calling adoption for less capable models

Replace pseudo-syntax examples with JSON Tool:/Arguments: format in system
prompt and orchestration reminders. Add parameter hints to tool summaries,
improve error messages with usage examples, and strengthen delegation nudges.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/agent/context.go

@@ -21,21 +21,29 @@ const orchestrationGuidance = `## Orchestration
 
 You are the conductor, not the performer. **Your primary job is to delegate, not to implement.**
 
-### spawn (non-blocking) — default choice
-- Tasks that can run in parallel or in the background
-- Multiple independent tasks — spawn each one simultaneously
-- Long-running operations (implementation, test suites, analysis)
-- Any work that involves more than 2-3 tool calls
+### spawn (non-blocking) — DEFAULT choice
+Returns immediately. Use for any task that can run independently.
+Call the spawn tool with JSON arguments like this:
 
-### subagent (blocking) — when you need the answer now
-- You need the result before deciding the next step
-- Correctness of your next action depends on the outcome
+Tool: spawn
+Arguments: {"task": "Examine pkg/auth/ and report middleware pattern", "preset": "scout", "label": "auth-scout"}
 
-### Inline — only for trivial operations
-- A single fast tool call (read one file, quick search)
-- Overhead of delegation clearly outweighs the benefit
+Tool: spawn
+Arguments: {"task": "Implement rate limiter in pkg/ratelimit/ with tests", "preset": "coder", "label": "rate-limiter"}
 
-### Presets
+### subagent (blocking) — only when you need the answer NOW
+Blocks until the subagent finishes. Use only when you cannot proceed without the result.
+Does not take a preset — it runs with default tools.
+
+Tool: subagent
+Arguments: {"task": "Read pkg/config/config.go and list all SubagentsConfig fields", "label": "config-check"}
+
+### When to use which
+- spawn: parallel tasks, independent work, implementation, long analysis, >2 tool calls
+- subagent: you need the result before your next decision
+- inline: single quick tool call where delegation overhead is wasteful
+
+### Presets (for spawn only)
 | preset | role | can write | can exec |
 |--------|------|-----------|----------|
 | scout | explore, investigate | no | no |
@@ -44,20 +52,14 @@ You are the conductor, not the performer. **Your primary job is to delegate, not
 | worker | build + install | yes (sandbox) | build/package mgr |
 | coordinator | orchestrate others | yes (sandbox) | general + spawn |
 
-### Examples
+### Parallel spawning
+Spawn multiple independent tasks at once — do NOT wait between them:
 
-Investigate code structure:
-  spawn(task: "Examine pkg/auth/ and report middleware pattern and entry points", preset: "scout", label: "auth-scout")
+Tool: spawn
+Arguments: {"task": "Analyze error handling patterns in pkg/providers/", "preset": "analyst", "label": "error-patterns"}
 
-Implement a feature:
-  spawn(task: "Implement rate limiter in pkg/ratelimit/ with tests. Run go test to verify.", preset: "coder", label: "rate-limiter")
-
-Get a blocking answer:
-  subagent(task: "Read pkg/config/config.go and list all SubagentsConfig fields", label: "config-check")
-
-Parallel exploration:
-  spawn(task: "Analyze error handling patterns in pkg/providers/", preset: "analyst", label: "error-patterns")
-  spawn(task: "List all HTTP endpoints in pkg/miniapp/", preset: "scout", label: "endpoints")
+Tool: spawn
+Arguments: {"task": "List all HTTP endpoints in pkg/miniapp/", "preset": "scout", "label": "endpoints"}
 
 After spawning, record the assignment in ## Orchestration > Delegated in MEMORY.md.
 When results come back, synthesize findings and decide the next fork.`

pkg/agent/loop.go

@@ -1270,9 +1270,15 @@ func buildOrchReminder(iteration int) (providers.Message, bool) {
 	if iteration != 1 && iteration%3 != 0 {
 		return providers.Message{}, false
 	}
-	content := "[System] ORCHESTRATION mode active. Delegate plan steps to subagents using spawn (async) or subagent (blocking). " +
-		"Do NOT implement steps inline unless they are trivial single-tool-call tasks. " +
-		"Spawn multiple independent steps in parallel for maximum throughput."
+	content := `[System] ORCHESTRATION mode active. You MUST delegate plan steps to subagents.
+Use spawn (non-blocking, returns immediately) or subagent (blocking, waits for result).
+Do NOT implement steps inline unless they are a single trivial tool call.
+
+To delegate, call the tool with JSON arguments:
+  Tool: spawn  Arguments: {"task": "...", "preset": "scout", "label": "..."}
+  Tool: subagent  Arguments: {"task": "...", "label": "..."}
+
+Spawn multiple independent steps in parallel for maximum throughput.`
 	return providers.Message{Role: "user", Content: content}, true
 }
 

pkg/tools/registry.go

@@ -227,8 +227,45 @@ func (r *ToolRegistry) GetRuntimeStatus() string {
 	return strings.Join(parts, "\n\n")
 }
 
+// buildParamHint extracts parameter names from a JSON schema and returns
+// a hint string like "(task, label?, preset?)". Required params are bare,
+// optional params have a trailing "?".
+func buildParamHint(schema map[string]any) string {
+	props, _ := schema["properties"].(map[string]any)
+	if len(props) == 0 {
+		return ""
+	}
+
+	reqSlice, _ := schema["required"].([]string)
+	reqSet := make(map[string]bool, len(reqSlice))
+	for _, r := range reqSlice {
+		reqSet[r] = true
+	}
+
+	names := make([]string, 0, len(props))
+	for name := range props {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+
+	parts := make([]string, 0, len(names))
+	// Required params first, then optional
+	for _, name := range names {
+		if reqSet[name] {
+			parts = append(parts, name)
+		}
+	}
+	for _, name := range names {
+		if !reqSet[name] {
+			parts = append(parts, name+"?")
+		}
+	}
+
+	return "(" + strings.Join(parts, ", ") + ")"
+}
+
 // GetSummaries returns human-readable summaries of all registered tools.
-// Returns a slice of "name - description" strings.
+// Returns a slice of "- `name`(params) - description" strings.
 func (r *ToolRegistry) GetSummaries() []string {
 	r.mu.RLock()
 	defer r.mu.RUnlock()
@@ -237,7 +274,8 @@ func (r *ToolRegistry) GetSummaries() []string {
 	summaries := make([]string, 0, len(sorted))
 	for _, name := range sorted {
 		tool := r.tools[name]
-		summaries = append(summaries, fmt.Sprintf("- `%s` - %s", tool.Name(), tool.Description()))
+		hint := buildParamHint(tool.Parameters())
+		summaries = append(summaries, fmt.Sprintf("- `%s`%s - %s", tool.Name(), hint, tool.Description()))
 	}
 	return summaries
 }

pkg/tools/registry_test.go

@@ -337,6 +337,78 @@ func TestToolRegistry_Count(t *testing.T) {
 	}
 }
 
+func TestBuildParamHint(t *testing.T) {
+	tests := []struct {
+		name   string
+		schema map[string]any
+		want   string
+	}{
+		{
+			name: "required and optional",
+			schema: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"task":  map[string]any{"type": "string"},
+					"label": map[string]any{"type": "string"},
+				},
+				"required": []string{"task"},
+			},
+			want: "(task, label?)",
+		},
+		{
+			name: "all required",
+			schema: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"command": map[string]any{"type": "string"},
+				},
+				"required": []string{"command"},
+			},
+			want: "(command)",
+		},
+		{
+			name: "no properties",
+			schema: map[string]any{
+				"type": "object",
+			},
+			want: "",
+		},
+		{
+			name:   "empty schema",
+			schema: map[string]any{},
+			want:   "",
+		},
+		{
+			name:   "nil schema",
+			schema: nil,
+			want:   "",
+		},
+		{
+			name: "multiple optional sorted",
+			schema: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"task":     map[string]any{"type": "string"},
+					"preset":   map[string]any{"type": "string"},
+					"label":    map[string]any{"type": "string"},
+					"agent_id": map[string]any{"type": "string"},
+				},
+				"required": []string{"task"},
+			},
+			want: "(task, agent_id?, label?, preset?)",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := buildParamHint(tt.schema)
+			if got != tt.want {
+				t.Errorf("buildParamHint() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestToolRegistry_GetSummaries(t *testing.T) {
 	r := NewToolRegistry()
 	r.Register(newMockTool("read_file", "Reads a file"))
@@ -353,6 +425,32 @@ func TestToolRegistry_GetSummaries(t *testing.T) {
 	}
 }
 
+func TestToolRegistry_GetSummaries_WithParamHint(t *testing.T) {
+	r := NewToolRegistry()
+	r.Register(&mockRegistryTool{
+		name: "spawn",
+		desc: "Spawn a subagent",
+		params: map[string]any{
+			"type": "object",
+			"properties": map[string]any{
+				"task":   map[string]any{"type": "string"},
+				"preset": map[string]any{"type": "string"},
+			},
+			"required": []string{"task"},
+		},
+		result: SilentResult("ok"),
+	})
+
+	summaries := r.GetSummaries()
+	if len(summaries) != 1 {
+		t.Fatalf("expected 1 summary, got %d", len(summaries))
+	}
+	// Should contain param hint
+	if !strings.Contains(summaries[0], "(task, preset?)") {
+		t.Errorf("expected param hint in summary, got %q", summaries[0])
+	}
+}
+
 func TestToolToSchema(t *testing.T) {
 	tool := newMockTool("demo", "demo tool")
 	schema := ToolToSchema(tool)

pkg/tools/spawn.go

@@ -32,7 +32,7 @@ func (t *SpawnTool) Name() string {
 }
 
 func (t *SpawnTool) Description() string {
-	return "Spawn a subagent to handle a task in the background. Use this for complex or time-consuming tasks that can run independently. The subagent will complete the task and report back when done."
+	return "Spawn a subagent that runs NON-BLOCKING in the background and returns immediately. Prefer this over subagent for any task that can run independently. Use preset to control capabilities (scout, analyst, coder, worker, coordinator)."
 }
 
 func (t *SpawnTool) Parameters() map[string]any {
@@ -73,7 +73,7 @@ func (t *SpawnTool) SetAllowlistChecker(check func(targetAgentID string) bool) {
 func (t *SpawnTool) Execute(ctx context.Context, args map[string]any) *ToolResult {
 	task, ok := args["task"].(string)
 	if !ok || strings.TrimSpace(task) == "" {
-		return ErrorResult("task is required and must be a non-empty string")
+		return ErrorResult(`Required parameter "task" (string) is missing. Example: {"task": "describe what you need done", "preset": "scout"}`)
 	}
 
 	label, _ := args["label"].(string)
@@ -87,12 +87,12 @@ func (t *SpawnTool) Execute(ctx context.Context, args map[string]any) *ToolResul
 	}
 	if checkTarget != "" && t.allowlistCheck != nil {
 		if !t.allowlistCheck(checkTarget) {
-			return ErrorResult(fmt.Sprintf("not allowed to spawn agent '%s' or preset '%s'", agentID, preset))
+			return ErrorResult(fmt.Sprintf("preset %q is not allowed. Available presets: scout, analyst, coder, worker, coordinator", preset))
 		}
 	}
 
 	if t.manager == nil {
-		return ErrorResult("Subagent manager not configured")
+		return ErrorResult("spawn tool is not available in this session (orchestration may be disabled)")
 	}
 
 	// Pass callback to manager for async completion notification

pkg/tools/subagent.go

@@ -384,7 +384,7 @@ func (t *SubagentTool) Name() string {
 }
 
 func (t *SubagentTool) Description() string {
-	return "Execute a subagent task synchronously and return the result. Use this for delegating specific tasks to an independent agent instance. Returns execution summary to user and full details to LLM."
+	return "Run a task in a subagent and BLOCK until it completes, returning the result directly. Use when you need the answer before deciding your next step. For background/parallel tasks, use spawn instead."
 }
 
 func (t *SubagentTool) Parameters() map[string]any {
@@ -412,13 +412,15 @@ func (t *SubagentTool) SetContext(channel, chatID string) {
 func (t *SubagentTool) Execute(ctx context.Context, args map[string]any) *ToolResult {
 	task, ok := args["task"].(string)
 	if !ok {
-		return ErrorResult("task is required").WithError(fmt.Errorf("task parameter is required"))
+		return ErrorResult(`Required parameter "task" (string) is missing. Example: {"task": "describe what you need done"}`).
+			WithError(fmt.Errorf("task parameter is required"))
 	}
 
 	label, _ := args["label"].(string)
 
 	if t.manager == nil {
-		return ErrorResult("Subagent manager not configured").WithError(fmt.Errorf("manager is nil"))
+		return ErrorResult("subagent tool is not available in this session (orchestration may be disabled)").
+			WithError(fmt.Errorf("manager is nil"))
 	}
 
 	// Build messages for subagent

pkg/tools/subagent_tool_test.go

@@ -93,8 +93,11 @@ func TestSubagentTool_Description(t *testing.T) {
 	if desc == "" {
 		t.Error("Description should not be empty")
 	}
-	if !strings.Contains(desc, "subagent") {
-		t.Errorf("Description should mention 'subagent', got: %s", desc)
+	if !strings.Contains(desc, "BLOCK") {
+		t.Errorf("Description should mention 'BLOCK', got: %s", desc)
+	}
+	if !strings.Contains(desc, "spawn") {
+		t.Errorf("Description should contrast with spawn, got: %s", desc)
 	}
 }
 
@@ -259,9 +262,12 @@ func TestSubagentTool_Execute_MissingTask(t *testing.T) {
 		t.Error("Expected error for missing task parameter")
 	}
 
-	// ForLLM should contain error message
-	if !strings.Contains(result.ForLLM, "task is required") {
-		t.Errorf("Error message should mention 'task is required', got: %s", result.ForLLM)
+	// ForLLM should contain helpful error with example
+	if !strings.Contains(result.ForLLM, `"task"`) {
+		t.Errorf("Error message should mention '\"task\"', got: %s", result.ForLLM)
+	}
+	if !strings.Contains(result.ForLLM, "Example") {
+		t.Errorf("Error message should include usage example, got: %s", result.ForLLM)
 	}
 
 	// Err should be set
@@ -286,8 +292,8 @@ func TestSubagentTool_Execute_NilManager(t *testing.T) {
 		t.Error("Expected error for nil manager")
 	}
 
-	if !strings.Contains(result.ForLLM, "Subagent manager not configured") {
-		t.Errorf("Error message should mention manager not configured, got: %s", result.ForLLM)
+	if !strings.Contains(result.ForLLM, "not available in this session") {
+		t.Errorf("Error message should mention 'not available in this session', got: %s", result.ForLLM)
 	}
 }