feat: preserve historical images in multi turn conversations

backend/internal/application/conversation/service.go

@@ -99,6 +99,7 @@ type Service struct {
 	snapshotCache     sync.Map // conversationID (uint) → *cachedSnapshot
 	userMemCache      sync.Map // userID (uint) → *cachedUserMemories
 	userSettingCache  sync.Map // "userID:key" (string) → *cachedUserSetting
+	imageContextCache *preparedConversationImageCache
 }
 
 func (s *Service) llmAttribution() (string, string) {
@@ -133,6 +134,7 @@ type AttachmentInput struct {
 	RagOptOut              bool // 用户是否关闭该文件的 RAG；RAG 段直接复用，无需重查 DB
 	ChunkCount             int  // 向量分块数；RAG 缓存 key 需要
 	Current                bool // 是否为本轮用户显式上传的附件
+	MessageRole            string
 	ContextMode            string
 }
 
@@ -253,6 +255,7 @@ func NewServiceWithRuntime(
 		storeProvider:     appstorage.NewRuntimeProvider(cfg, nil),
 		logger:            logger,
 		generationStreams: newGenerationStreamRegistry(cache, defaultGenerationStreamOptions()),
+		imageContextCache: defaultPreparedConversationImageCache(),
 	}
 	if extractSvc == nil {
 		extractSvc = extraction.NewServiceWithRuntime(cfg)

backend/internal/application/conversation/service_branch.go

@@ -11,6 +11,8 @@ import (
 	"go.uber.org/zap"
 )
 
+const estimatedConversationImageTokens int64 = 1024
+
 type messageBranchState struct {
 	ExistingMessages []model.Message
 	ParentMessageID  *uint
@@ -311,8 +313,9 @@ func truncateContextByTokenBudget(messages []model.Message, budgetTokens int, in
 	}
 	total := 0
 	cutFrom := len(messages)
+	imageTokenReserve := conversationImageTokenReserveByMessage(messages)
 	for i := len(messages) - 1; i >= 0; i-- {
-		msgTokens := int(estimateDomainMessageTokens(messages[i], includeReasoningContent))
+		msgTokens := int(estimateDomainMessageTokens(messages[i], includeReasoningContent) + imageTokenReserve[i])
 		if total+msgTokens > budgetTokens && cutFrom < len(messages) {
 			break
 		}
@@ -322,6 +325,28 @@ func truncateContextByTokenBudget(messages []model.Message, budgetTokens int, in
 	return messages[cutFrom:]
 }
 
+func conversationImageTokenReserveByMessage(messages []model.Message) map[int]int64 {
+	reserve := make(map[int]int64)
+	remaining := maxConversationImageContextCount
+	for messageIndex := len(messages) - 1; messageIndex >= 0 && remaining > 0; messageIndex-- {
+		message := messages[messageIndex]
+		if !strings.EqualFold(strings.TrimSpace(message.Role), "user") {
+			continue
+		}
+		refs := parseAttachmentSnapshotRefs(message.Attachments)
+		for attachmentIndex := len(refs) - 1; attachmentIndex >= 0 && remaining > 0; attachmentIndex-- {
+			ref := refs[attachmentIndex]
+			mimeType := firstNonEmptyString(ref.DetectedMIME, ref.MimeType)
+			if normalizeAttachmentKind(ref.Kind, mimeType) != "image" {
+				continue
+			}
+			reserve[messageIndex] += estimatedConversationImageTokens
+			remaining--
+		}
+	}
+	return reserve
+}
+
 func estimateDomainMessageTokens(message model.Message, includeReasoningContent bool) int64 {
 	tokens := estimateTokens(message.Content)
 	if includeReasoningContent && message.Role == "assistant" {

backend/internal/application/conversation/service_branch_test.go

@@ -296,6 +296,19 @@ func TestTruncateContextByTokenBudgetCountsAssistantReasoningWhenEnabled(t *test
 	}
 }
 
+func TestTruncateContextByTokenBudgetReservesHistoricalImageTokens(t *testing.T) {
+	messages := []model.Message{
+		{ID: 1, Role: "user", Content: "first", Attachments: `[{"file_id":"image_1","kind":"image","mime_type":"image/png"}]`},
+		{ID: 2, Role: "assistant", Content: "ok"},
+		{ID: 3, Role: "user", Content: "next"},
+	}
+
+	got := truncateContextByTokenBudget(messages, 100, false)
+	if len(got) != 2 || got[0].ID != 2 || got[1].ID != 3 {
+		t.Fatalf("expected image token reserve to trim the oldest image turn, got %#v", got)
+	}
+}
+
 func TestBuildBranchMessagePathReusesExistingUserForAssistantRetry(t *testing.T) {
 	rootID := uint(1)
 	userID := uint(2)

backend/internal/application/conversation/service_file_context.go

@@ -19,7 +19,10 @@ const (
 )
 
 type attachmentSnapshotRef struct {
-	FileID string `json:"file_id"`
+	FileID       string `json:"file_id"`
+	Kind         string `json:"kind"`
+	MimeType     string `json:"mime_type"`
+	DetectedMIME string `json:"detected_mime"`
 }
 
 type conversationFileContextPlan struct {
@@ -59,6 +62,17 @@ func collectConversationFileIDs(messages []model.Message, currentFileIDs []strin
 }
 
 func parseAttachmentSnapshotFileIDs(raw string) []string {
+	items := parseAttachmentSnapshotRefs(raw)
+	result := make([]string, 0, len(items))
+	for _, item := range items {
+		if fileID := strings.TrimSpace(item.FileID); fileID != "" {
+			result = append(result, fileID)
+		}
+	}
+	return result
+}
+
+func parseAttachmentSnapshotRefs(raw string) []attachmentSnapshotRef {
 	payload := strings.TrimSpace(raw)
 	if payload == "" || payload == "[]" {
 		return nil
@@ -67,13 +81,7 @@ func parseAttachmentSnapshotFileIDs(raw string) []string {
 	if err := json.Unmarshal([]byte(payload), &items); err != nil {
 		return nil
 	}
-	result := make([]string, 0, len(items))
-	for _, item := range items {
-		if fileID := strings.TrimSpace(item.FileID); fileID != "" {
-			result = append(result, fileID)
-		}
-	}
-	return result
+	return items
 }
 
 func filterCurrentAttachments(items []AttachmentInput) []AttachmentInput {
@@ -86,6 +94,29 @@ func filterCurrentAttachments(items []AttachmentInput) []AttachmentInput {
 	return result
 }
 
+func bindAttachmentMessageRoles(items []AttachmentInput, messages []model.Message) []AttachmentInput {
+	if len(items) == 0 || len(messages) == 0 {
+		return items
+	}
+	roles := make(map[string]string)
+	for _, message := range messages {
+		role := strings.ToLower(strings.TrimSpace(message.Role))
+		if role != "user" && role != "assistant" {
+			continue
+		}
+		for _, fileID := range parseAttachmentSnapshotFileIDs(message.Attachments) {
+			if role == "user" || roles[fileID] == "" {
+				roles[fileID] = role
+			}
+		}
+	}
+	result := append([]AttachmentInput(nil), items...)
+	for index := range result {
+		result[index].MessageRole = roles[strings.TrimSpace(result[index].FileID)]
+	}
+	return result
+}
+
 func filterAttachmentsByContextMode(items []AttachmentInput, contextMode string) []AttachmentInput {
 	result := make([]AttachmentInput, 0)
 	for _, item := range items {
@@ -105,6 +136,9 @@ func isStableTextAttachment(item AttachmentInput) bool {
 
 func shouldShowAttachmentProcessTrace(items []AttachmentInput) bool {
 	for _, item := range items {
+		if strings.EqualFold(strings.TrimSpace(item.ContextMode), fileContextModeDirectImage) && !item.Current {
+			continue
+		}
 		if item.Current {
 			return true
 		}
@@ -115,6 +149,17 @@ func shouldShowAttachmentProcessTrace(items []AttachmentInput) bool {
 	return false
 }
 
+func attachmentProcessTraceItems(items []AttachmentInput) []AttachmentInput {
+	result := make([]AttachmentInput, 0, len(items))
+	for _, item := range items {
+		if strings.EqualFold(strings.TrimSpace(item.ContextMode), fileContextModeDirectImage) && !item.Current {
+			continue
+		}
+		result = append(result, item)
+	}
+	return result
+}
+
 func buildConversationFileContextPlan(
 	attachments []AttachmentInput,
 	fileMode string,
@@ -128,7 +173,7 @@ func buildConversationFileContextPlan(
 	}
 	for _, item := range attachments {
 		kind := normalizeAttachmentKind(item.Kind, item.DetectedMIME)
-		if kind == "image" && item.Current {
+		if kind == "image" && (item.Current || strings.EqualFold(strings.TrimSpace(item.MessageRole), "user")) {
 			item.ContextMode = fileContextModeDirectImage
 			plan.Attachments = append(plan.Attachments, item)
 			plan.FullAttachments = append(plan.FullAttachments, item)