feat(chat): stop active llm responses

backend/AGENTS.md

@@ -66,6 +66,7 @@ web/                    # Embedded static assets (embed.go)
 | POST     | `/api/chats/{chatId}`         | PostChatMessage    |
 | DELETE   | `/api/chats/{chatId}`         | DeleteChat         |
 | GET      | `/api/chats/{chatId}/stream`  | GetChatStream      |
+| POST     | `/api/chats/{chatId}/stop`    | StopChatGeneration |
 
 ## Testing
 

backend/internal/api/generation.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"errors"
 	"slices"
 	"sync"
@@ -19,6 +20,8 @@ type generationManager struct {
 
 type generation struct {
 	mu          sync.RWMutex
+	ctx         context.Context
+	cancel      context.CancelFunc
 	subscribers map[chan *MessageChunk]struct{}
 	done        chan struct{}
 	closed      bool
@@ -36,7 +39,10 @@ func (m *generationManager) start(chatID uuid.UUID, prepare func(*generation) er
 	}
 
 	// Reserve Generation
+	ctx, cancel := context.WithCancel(context.Background())
 	gen := &generation{
+		ctx:         ctx,
+		cancel:      cancel,
 		subscribers: make(map[chan *MessageChunk]struct{}),
 		done:        make(chan struct{}),
 	}
@@ -79,6 +85,19 @@ func (m *generationManager) subscribe(chatID uuid.UUID) (<-chan *MessageChunk, f
 	return ch, func() { gen.unsubscribe(ch) }, true
 }
 
+func (m *generationManager) stop(chatID uuid.UUID) bool {
+	m.mu.RLock()
+	gen, found := m.generations[chatID]
+	m.mu.RUnlock()
+	if !found {
+		return false
+	}
+
+	// Cancel Generation
+	gen.cancel()
+	return true
+}
+
 func (g *generation) subscribe() chan *MessageChunk {
 	ch := make(chan *MessageChunk, 64)
 
@@ -126,6 +145,7 @@ func (g *generation) close() {
 		return
 	}
 	g.closed = true
+	g.cancel()
 	close(g.done)
 	for subscriber := range g.subscribers {
 		close(subscriber)

backend/internal/api/handlers.go

@@ -449,6 +449,32 @@ func (a *API) GetChatStream(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (a *API) StopChatGeneration(w http.ResponseWriter, r *http.Request) {
+	log := a.logger.WithField("handler", "StopChatGenerationHandler")
+
+	// Parse Chat ID
+	rawChatID := r.PathValue("chatId")
+	if rawChatID == "" {
+		log.Error("missing chat ID parameter")
+		http.Error(w, "Chat ID is required", http.StatusBadRequest)
+		return
+	}
+	chatID, err := uuid.Parse(rawChatID)
+	if err != nil {
+		log.WithError(err).Error("invalid chat ID format")
+		http.Error(w, "Invalid chat ID format", http.StatusBadRequest)
+		return
+	}
+
+	// Stop Generation
+	if !a.generationManager.stop(chatID) {
+		http.Error(w, "Chat generation is not active", http.StatusNotFound)
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}
+
 func (a *API) PostChatMessage(w http.ResponseWriter, r *http.Request) {
 	log := a.logger.WithField("handler", "PostChatMessageHandler")
 
@@ -563,7 +589,7 @@ func (a *API) startMessageGeneration(chatID uuid.UUID, chatModel, userMessage st
 
 func (a *API) runMessageGeneration(apiClient *client.Client, chat *store.Chat, assistantMsg *store.Message, chatModel string, gen *generation) {
 	// Create Generation Context
-	ctx, cancel := context.WithTimeout(context.Background(), time.Minute*5)
+	ctx, cancel := context.WithTimeout(gen.ctx, time.Minute*5)
 	defer cancel()
 
 	// Send Message
@@ -593,15 +619,37 @@ func (a *API) runMessageGeneration(apiClient *client.Client, chat *store.Chat, a
 
 		return nil
 	}); err != nil {
-		assistantMsg.Status = store.MessageStatusFailed
+		// Handle Stopped Generation
+		if errors.Is(gen.ctx.Err(), context.Canceled) {
+			assistantMsg.Status = store.MessageStatusStopped
+			if saveErr := a.store.SaveChatMessage(assistantMsg); saveErr != nil {
+				a.logger.WithError(saveErr).WithField("chat_id", chat.ID).Error("failed to save stopped assistant message")
+			}
+			gen.broadcast(&MessageChunk{AssistantMessage: assistantMsg})
+			return
+		}
+
+		// Handle Error Generation
+		assistantMsg.Status = store.MessageStatusError
 		if saveErr := a.store.SaveChatMessage(assistantMsg); saveErr != nil {
-			a.logger.WithError(saveErr).WithField("chat_id", chat.ID).Error("failed to save failed assistant message")
+			a.logger.WithError(saveErr).WithField("chat_id", chat.ID).Error("failed to save errored assistant message")
 		}
 		gen.broadcast(&MessageChunk{AssistantMessage: assistantMsg})
 		a.logger.WithError(err).WithField("chat_id", chat.ID).Error("failed to generate text stream")
 		return
 	}
 
+	// Handle Stopped Generation
+	if errors.Is(gen.ctx.Err(), context.Canceled) {
+		assistantMsg.Status = store.MessageStatusStopped
+		if err := a.store.SaveChatMessage(assistantMsg); err != nil {
+			a.logger.WithError(err).WithField("chat_id", chat.ID).Error("failed to save stopped assistant message")
+			return
+		}
+		gen.broadcast(&MessageChunk{AssistantMessage: assistantMsg})
+		return
+	}
+
 	// Summarize & Update Chat Title
 	if chat.Title == "" {
 		var err error

backend/internal/server/server.go

@@ -49,6 +49,7 @@ func StartServer(settingsStore store.Store, dataDir, staticDir, listenAddress st
 	mux.HandleFunc("POST /api/chats", api.PostChat)
 	mux.HandleFunc("GET /api/chats/{chatId}", api.GetChat)
 	mux.HandleFunc("GET /api/chats/{chatId}/stream", api.GetChatStream)
+	mux.HandleFunc("POST /api/chats/{chatId}/stop", api.StopChatGeneration)
 	mux.HandleFunc("POST /api/chats/{chatId}", api.PostChatMessage)
 	mux.HandleFunc("DELETE /api/chats/{chatId}", api.DeleteChat)
 

backend/internal/store/types.go

@@ -33,7 +33,8 @@ type MessageStatus string
 const (
 	MessageStatusStreaming MessageStatus = "streaming"
 	MessageStatusComplete  MessageStatus = "complete"
-	MessageStatusFailed    MessageStatus = "failed"
+	MessageStatusStopped   MessageStatus = "stopped"
+	MessageStatusError     MessageStatus = "error"
 )
 
 type Message struct {