config: add tools bool to disable tool collection per agent

When tools is false in agent config, BuildAgentEnv skips ListTools
entirely so no tool schemas are sent to the backend. Models without
tool support now work cleanly.

pkg/agent/core.go

@@ -47,18 +47,22 @@ type AgentEnv struct {
 func BuildAgentEnv(cfg *config.Config, d tools.Dispatcher, cwd string) AgentEnv {
 	var messages []string
 
-	allToolInfos, listErr := d.ListTools()
-	if listErr != nil {
-		messages = append(messages, fmt.Sprintf("list tools: %v", listErr))
-	}
+	var allToolInfos []tools.ToolInfo
+	var allTools []backend.Tool
+	serverOf := make(map[string]string)
 
-	serverOf := make(map[string]string, len(allToolInfos))
-	for _, t := range allToolInfos {
-		serverOf[t.Name] = t.Server
+	if cfg == nil || cfg.ToolsEnabled() {
+		var listErr error
+		allToolInfos, listErr = d.ListTools()
+		if listErr != nil {
+			messages = append(messages, fmt.Sprintf("list tools: %v", listErr))
+		}
+		for _, t := range allToolInfos {
+			serverOf[t.Name] = t.Server
+		}
+		allTools = toolInfosToBackend(allToolInfos)
 	}
 
-	allTools := toolInfosToBackend(allToolInfos)
-
 	hooks := Hooks{}
 	var preamble string
 	var genParams backend.GenerationParams

pkg/agent/core_test.go

@@ -2335,6 +2335,19 @@ func TestBuildAgentEnv_ToolsPopulated(t *testing.T) {
 	}
 }
 
+func TestBuildAgentEnv_ToolsDisabled(t *testing.T) {
+	setupCfgDir(t)
+	d := &mockDispatcher{
+		tools: []tools.ToolInfo{{Server: "s1", Name: "mytool", Description: "desc", InputSchema: json.RawMessage(`{}`)}},
+	}
+	f := false
+	cfg := &config.Config{Tools: &f}
+	env := BuildAgentEnv(cfg, d, t.TempDir())
+	if len(env.tools) != 0 {
+		t.Errorf("expected no tools when disabled; got %+v", env.tools)
+	}
+}
+
 func TestBuildAgentEnv_TrustedTools(t *testing.T) {
 	setupCfgDir(t)
 	setter := &mockTrustedSetter{}

pkg/config/config.go

@@ -61,6 +61,7 @@ func (p Prompt) MarshalJSON() ([]byte, error) {
 type Config struct {
 	Hooks            map[string]HookCmds     `json:"hooks,omitempty"`
 	Prompt           Prompt                  `json:"prompt,omitempty"`
+	Tools            *bool                   `json:"tools,omitempty"`
 	TrustedTools     []string                `json:"trustedTools,omitempty"`
 	MaxTokens        int                     `json:"maxTokens,omitempty"`
 	Temperature      *float64                `json:"temperature,omitempty"`
@@ -76,3 +77,9 @@ func Load(r io.Reader) (*Config, error) {
 	}
 	return &cfg, nil
 }
+
+// ToolsEnabled reports whether tool use is enabled. Defaults to true when
+// the field is omitted from the config.
+func (c *Config) ToolsEnabled() bool {
+	return c.Tools == nil || *c.Tools
+}

pkg/config/config_test.go

@@ -121,3 +121,21 @@ func TestLoadAllFields(t *testing.T) {
 		t.Errorf("PresencePenalty = %v", cfg.PresencePenalty)
 	}
 }
+
+func TestToolsEnabled(t *testing.T) {
+	// Omitted: defaults to true.
+	cfg, _ := Load(strings.NewReader(`{}`))
+	if !cfg.ToolsEnabled() {
+		t.Error("expected ToolsEnabled()=true when omitted")
+	}
+	// Explicit false.
+	cfg, _ = Load(strings.NewReader(`{"tools": false}`))
+	if cfg.ToolsEnabled() {
+		t.Error("expected ToolsEnabled()=false")
+	}
+	// Explicit true.
+	cfg, _ = Load(strings.NewReader(`{"tools": true}`))
+	if !cfg.ToolsEnabled() {
+		t.Error("expected ToolsEnabled()=true")
+	}
+}