feat: add chat history persistence and agent web search

- Add file-based conversation storage under ~/.csghub-lite/conversations/
  with REST API for CRUD operations
- Add automatic web search agent: LLM decides when to search, backend
  injects tool and executes DuckDuckGo/Searxng queries transparently
- Rewrite Chat.tsx with conversation sidebar, backend-backed sessions,
  and searching indicator
- No new Go dependencies added

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ganisback

internal/chathistory/store.go

@@ -0,0 +1,180 @@
+package chathistory
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/opencsgs/csghub-lite/pkg/api"
+)
+
+const conversationsDir = "conversations"
+
+type Store struct {
+	dir string
+	mu  sync.RWMutex
+}
+
+func NewStore(appHome string) *Store {
+	dir := filepath.Join(appHome, conversationsDir)
+	os.MkdirAll(dir, 0o755)
+	return &Store{dir: dir}
+}
+
+func (s *Store) List() ([]api.ConversationMeta, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	entries, err := os.ReadDir(s.dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("reading conversations dir: %w", err)
+	}
+
+	var metas []api.ConversationMeta
+	for _, e := range entries {
+		if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
+			continue
+		}
+		data, err := os.ReadFile(filepath.Join(s.dir, e.Name()))
+		if err != nil {
+			continue
+		}
+		var conv api.Conversation
+		if err := json.Unmarshal(data, &conv); err != nil {
+			continue
+		}
+		metas = append(metas, api.ConversationMeta{
+			ID:        conv.ID,
+			Title:     conv.Title,
+			Model:     conv.Model,
+			CreatedAt: conv.CreatedAt,
+			UpdatedAt: conv.UpdatedAt,
+			MsgCount:  len(conv.Messages),
+		})
+	}
+
+	sort.Slice(metas, func(i, j int) bool {
+		return metas[i].UpdatedAt.After(metas[j].UpdatedAt)
+	})
+	return metas, nil
+}
+
+func (s *Store) Get(id string) (*api.Conversation, error) {
+	if !isValidID(id) {
+		return nil, fmt.Errorf("invalid conversation id")
+	}
+
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	data, err := os.ReadFile(s.filePath(id))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, fmt.Errorf("conversation %q not found", id)
+		}
+		return nil, err
+	}
+	var conv api.Conversation
+	if err := json.Unmarshal(data, &conv); err != nil {
+		return nil, fmt.Errorf("decoding conversation: %w", err)
+	}
+	return &conv, nil
+}
+
+func (s *Store) Save(conv *api.Conversation) error {
+	if conv.ID == "" || !isValidID(conv.ID) {
+		return fmt.Errorf("invalid conversation id")
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	data, err := json.MarshalIndent(conv, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encoding conversation: %w", err)
+	}
+
+	if err := os.MkdirAll(s.dir, 0o755); err != nil {
+		return err
+	}
+
+	tmpFile := s.filePath(conv.ID) + ".tmp"
+	if err := os.WriteFile(tmpFile, data, 0o644); err != nil {
+		return err
+	}
+	return os.Rename(tmpFile, s.filePath(conv.ID))
+}
+
+func (s *Store) Delete(id string) error {
+	if !isValidID(id) {
+		return fmt.Errorf("invalid conversation id")
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	err := os.Remove(s.filePath(id))
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return nil
+}
+
+func (s *Store) filePath(id string) string {
+	return filepath.Join(s.dir, id+".json")
+}
+
+func isValidID(id string) bool {
+	if id == "" || len(id) > 128 {
+		return false
+	}
+	for _, c := range id {
+		if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '-' || c == '_') {
+			return false
+		}
+	}
+	return true
+}
+
+func NewConversation() *api.Conversation {
+	now := time.Now()
+	return &api.Conversation{
+		ID:        generateID(),
+		Title:     "New Chat",
+		CreatedAt: now,
+		UpdatedAt: now,
+		Messages:  []api.Message{},
+	}
+}
+
+func generateID() string {
+	return fmt.Sprintf("%d-%s", time.Now().UnixMilli(), randomHex(8))
+}
+
+func randomHex(n int) string {
+	b := make([]byte, n)
+	f, err := os.Open("/dev/urandom")
+	if err != nil {
+		for i := range b {
+			b[i] = byte(time.Now().UnixNano() >> (i * 8))
+		}
+	} else {
+		f.Read(b)
+		f.Close()
+	}
+	const hex = "0123456789abcdef"
+	out := make([]byte, n*2)
+	for i, v := range b {
+		out[i*2] = hex[v>>4]
+		out[i*2+1] = hex[v&0x0f]
+	}
+	return string(out)
+}

internal/server/handlers.go

@@ -495,6 +495,11 @@ func (s *Server) handleChat(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if s.shouldInjectWebSearch(eng) {
+		s.handleChatWithWebSearch(w, r, req, eng, opts, stream)
+		return
+	}
+
 	if stream {
 		if requestWantsSSE(r) {
 			w.Header().Set("Content-Type", "text/event-stream")