refactor(tools): extract shared logic for internal channels and tool definitions

- Add constants package with IsInternalChannel helper to centralize internal channel checks across agent, channels, and heartbeat services
- Add ToProviderDefs method to ToolRegistry to consolidate tool definition conversion logic used in agent loop and tool loop
- Refactor SubagentTool.Execute to use RunToolLoop for consistent tool execution with iteration tracking
- Remove duplicate inline map definitions and type assertion code throughout codebase

pkg/agent/loop.go

@@ -19,6 +19,7 @@ import (
 
 	"github.com/sipeed/picoclaw/pkg/bus"
 	"github.com/sipeed/picoclaw/pkg/config"
+	"github.com/sipeed/picoclaw/pkg/constants"
 	"github.com/sipeed/picoclaw/pkg/logger"
 	"github.com/sipeed/picoclaw/pkg/providers"
 	"github.com/sipeed/picoclaw/pkg/session"
@@ -281,8 +282,7 @@ func (al *AgentLoop) processSystemMessage(ctx context.Context, msg bus.InboundMe
 	}
 
 	// Skip internal channels - only log, don't send to user
-	internalChannels := map[string]bool{"cli": true, "system": true, "subagent": true}
-	if internalChannels[originChannel] {
+	if constants.IsInternalChannel(originChannel) {
 		logger.InfoCF("agent", "Subagent completed (internal channel)",
 			map[string]interface{}{
 				"sender_id":    msg.SenderID,
@@ -311,8 +311,7 @@ func (al *AgentLoop) runAgentLoop(ctx context.Context, opts processOptions) (str
 	// 0. Record last channel for heartbeat notifications (skip internal channels)
 	if opts.Channel != "" && opts.ChatID != "" {
 		// Don't record internal channels (cli, system, subagent)
-		internalChannels := map[string]bool{"cli": true, "system": true, "subagent": true}
-		if !internalChannels[opts.Channel] {
+		if !constants.IsInternalChannel(opts.Channel) {
 			channelKey := fmt.Sprintf("%s:%s", opts.Channel, opts.ChatID)
 			if err := al.RecordLastChannel(channelKey); err != nil {
 				logger.WarnCF("agent", "Failed to record last channel: %v", map[string]interface{}{"error": err.Error()})
@@ -402,18 +401,7 @@ func (al *AgentLoop) runLLMIteration(ctx context.Context, messages []providers.M
 			})
 
 		// Build tool definitions
-		toolDefs := al.tools.GetDefinitions()
-		providerToolDefs := make([]providers.ToolDefinition, 0, len(toolDefs))
-		for _, td := range toolDefs {
-			providerToolDefs = append(providerToolDefs, providers.ToolDefinition{
-				Type: td["type"].(string),
-				Function: providers.ToolFunctionDefinition{
-					Name:        td["function"].(map[string]interface{})["name"].(string),
-					Description: td["function"].(map[string]interface{})["description"].(string),
-					Parameters:  td["function"].(map[string]interface{})["parameters"].(map[string]interface{}),
-				},
-			})
-		}
+		providerToolDefs := al.tools.ToProviderDefs()
 
 		// Log LLM request details
 		logger.DebugCF("agent", "LLM request",