refactor(commands): address code review findings on naming and correctness

- Rename dispatcher.go → request.go (no Dispatcher type remains)
- Rename cmd_agents.go → handler_agents.go (shared handler, not a top-level command)
- Add modelMu to protect AgentInstance.Model writes in SwitchModel
- Add ListDefinitions to Runtime so /help uses registry instead of BuiltinDefinitions()
- Fix SwitchChannel message: validation-only callback should not say "Switched"
- Propagate Reply errors in executor instead of discarding with _ =
- Add HasCommandPrefix unit test

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

pkg/agent/loop.go

@@ -48,6 +48,7 @@ type AgentLoop struct {
 	mediaStore     media.MediaStore
 	transcriber    voice.Transcriber
 	cmdRegistry    *commands.Registry
+	modelMu        sync.Mutex // protects AgentInstance.Model writes in SwitchModel
 }
 
 // processOptions configures how a message is processed
@@ -1510,6 +1511,7 @@ func (al *AgentLoop) buildCommandsRuntime() *commands.Runtime {
 			return agent.Model, al.cfg.Agents.Defaults.Provider
 		},
 		ListAgentIDs:    al.registry.ListAgentIDs,
+		ListDefinitions: al.cmdRegistry.Definitions,
 		GetEnabledChannels: func() []string {
 			if al.channelManager == nil {
 				return nil
@@ -1517,6 +1519,8 @@ func (al *AgentLoop) buildCommandsRuntime() *commands.Runtime {
 			return al.channelManager.GetEnabledChannels()
 		},
 		SwitchModel: func(value string) (string, error) {
+			al.modelMu.Lock()
+			defer al.modelMu.Unlock()
 			defaultAgent := al.registry.GetDefaultAgent()
 			if defaultAgent == nil {
 				return "", fmt.Errorf("no default agent configured")

pkg/commands/cmd_help.go

@@ -11,8 +11,13 @@ func helpCommand() Definition {
 		Name:        "help",
 		Description: "Show this help message",
 		Usage:       "/help",
-		Handler: func(_ context.Context, req Request, _ *Runtime) error {
-			defs := BuiltinDefinitions()
+		Handler: func(_ context.Context, req Request, rt *Runtime) error {
+			var defs []Definition
+			if rt != nil && rt.ListDefinitions != nil {
+				defs = rt.ListDefinitions()
+			} else {
+				defs = BuiltinDefinitions()
+			}
 			return req.Reply(formatHelpMessage(defs))
 		},
 	}

pkg/commands/cmd_switch.go

@@ -45,7 +45,7 @@ func switchCommand() Definition {
 					if err := rt.SwitchChannel(value); err != nil {
 						return req.Reply(err.Error())
 					}
-					return req.Reply(fmt.Sprintf("Switched target channel to %s", value))
+					return req.Reply(fmt.Sprintf("Channel '%s' is available and enabled", value))
 				},
 			},
 		},

pkg/commands/cmd_switch_test.go

@@ -141,7 +141,7 @@ func TestSwitchChannel_Success(t *testing.T) {
 	if res.Outcome != OutcomeHandled {
 		t.Fatalf("outcome=%v, want=%v", res.Outcome, OutcomeHandled)
 	}
-	want := "Switched target channel to telegram"
+	want := "Channel 'telegram' is available and enabled"
 	if reply != want {
 		t.Fatalf("reply=%q, want=%q", reply, want)
 	}

pkg/commands/executor.go

@@ -68,8 +68,8 @@ func (e *Executor) executeDefinition(ctx context.Context, req Request, def Defin
 	// Sub-command routing
 	subName := nthToken(req.Text, 1)
 	if subName == "" {
-		_ = req.Reply("Usage: " + def.EffectiveUsage())
-		return ExecuteResult{Outcome: OutcomeHandled, Command: def.Name}
+		err := req.Reply("Usage: " + def.EffectiveUsage())
+		return ExecuteResult{Outcome: OutcomeHandled, Command: def.Name, Err: err}
 	}
 
 	normalized := normalizeCommandName(subName)
@@ -84,6 +84,6 @@ func (e *Executor) executeDefinition(ctx context.Context, req Request, def Defin
 	}
 
 	// Unknown sub-command
-	_ = req.Reply(fmt.Sprintf("Unknown parameter: %s. Usage: %s", subName, def.EffectiveUsage()))
-	return ExecuteResult{Outcome: OutcomeHandled, Command: def.Name}
+	err := req.Reply(fmt.Sprintf("Unknown parameter: %s. Usage: %s", subName, def.EffectiveUsage()))
+	return ExecuteResult{Outcome: OutcomeHandled, Command: def.Name, Err: err}
 }

pkg/commands/request_test.go

@@ -0,0 +1,28 @@
+package commands
+
+import "testing"
+
+func TestHasCommandPrefix(t *testing.T) {
+	tests := []struct {
+		input string
+		want  bool
+	}{
+		{"/help", true},
+		{"!help", true},
+		{"/switch model to gpt-4", true},
+		{"!switch model to gpt-4", true},
+		{"hello", false},
+		{"", false},
+		{"   ", false},
+		{"hello /world", false},
+		{"/", true},
+		{"!", true},
+		{"  /help", true},
+	}
+	for _, tt := range tests {
+		got := HasCommandPrefix(tt.input)
+		if got != tt.want {
+			t.Errorf("HasCommandPrefix(%q) = %v, want %v", tt.input, got, tt.want)
+		}
+	}
+}

pkg/commands/runtime.go

@@ -9,6 +9,7 @@ type Runtime struct {
 	Config             *config.Config
 	GetModelInfo       func() (name, provider string)
 	ListAgentIDs       func() []string
+	ListDefinitions    func() []Definition
 	GetEnabledChannels func() []string
 	SwitchModel        func(value string) (oldModel string, err error)
 	SwitchChannel      func(value string) error