feat: output channel redesign - per-channel output gates, LLM chain events, SDKConfig

- Output channels generate per-channel tools: output_send__{name} (type=output) + output_send__{name}_help
- content is JSON string transparently passed to plugin handler for routing
- EventAgentLLMChain: full LLM response forwarded after each turn for webui/logs
- sdk.New refactored to SDKConfig struct (no more 13 positional args)
- RegisterOutputChannel adds desc param for JSON format documentation
- channelDevice simplified (no Tools method), desc field added
- Child agent permission updated for output_send__ prefix
- System prompt: output gates, multi-call, long messages split
- WebUI: subscribes to EventAgentLLMChain in SSE, no output channel
- Tests updated for new naming convention

internal/agent/io/channel.go

@@ -3,6 +3,7 @@ package io
 import (
 	"fmt"
 	"log"
+	"runtime/debug"
 	"sync"
 	"time"
 )
@@ -143,6 +144,12 @@ func (m *IOManager) RegisterDevice(dev Device) error {
 	return nil
 }
 
+func (m *IOManager) GetDevice(name string) Device {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.devices[name]
+}
+
 func (m *IOManager) StartAll() error {
 	m.mu.RLock()
 	devices := make([]Device, 0, len(m.devices))
@@ -336,7 +343,7 @@ func (m *IOManager) GetAllTools() []ToolDef {
 	return tools
 }
 
-func (m *IOManager) ExecuteTool(name string, args map[string]interface{}) (interface{}, error) {
+func (m *IOManager) ExecuteTool(name string, args map[string]interface{}) (ret interface{}, err error) {
 	m.mu.RLock()
 	type nameDevice struct {
 		name string
@@ -356,6 +363,12 @@ func (m *IOManager) ExecuteTool(name string, args map[string]interface{}) (inter
 	if len(candidates) == 0 {
 		return nil, fmt.Errorf("tool %s not found", name)
 	}
+	defer func() {
+		if r := recover(); r != nil {
+			log.Printf("[io] tool %s execute panic: %v\n%s", name, r, debug.Stack())
+			err = fmt.Errorf("tool %s execute panic: %v", name, r)
+		}
+	}()
 	return candidates[0].dev.Execute(name, args)
 }