fix(tasks): 任务队列 - 限制缓存回源并修复并发租约与过期写入

backend/internal/handler/routes.go

@@ -174,7 +174,7 @@ func RegisterTaskRoutes(r *gin.RouterGroup, svc *service.Service) {
 			fail(c, http.StatusBadRequest, err)
 			return
 		}
-		initial, err := svc.TaskTextReplay(user.ID, c.Param("id"), after)
+		initial, err := svc.CachedTaskTextReplay(c.Request.Context(), user.ID, c.Param("id"), after)
 		if err != nil {
 			failService(c, err)
 			return
@@ -308,7 +308,7 @@ func streamTaskTextEvents(c *gin.Context, svc *service.Service, userID string, t
 			c.Writer.Flush()
 		case <-pollTicker.C:
 		}
-		next, err := svc.TaskTextReplay(userID, taskID, after)
+		next, err := svc.CachedTaskTextReplay(c.Request.Context(), userID, taskID, after)
 		if err != nil {
 			writeTaskTextSSE(c, "error", 0, map[string]string{"message": "任务文本流不可用"})
 			return

backend/internal/handler/text_events_test.go

@@ -1,14 +1,19 @@
 package handler
 
 import (
+	"context"
 	"net/http/httptest"
 	"strings"
 	"testing"
+	"time"
 
 	"infinite-canvas/backend/internal/model"
+	"infinite-canvas/backend/internal/repository"
 	"infinite-canvas/backend/internal/service"
 
 	"github.com/gin-gonic/gin"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
 )
 
 func TestTaskTextEventCursorPrefersQueryAndSupportsLastEventID(t *testing.T) {
@@ -32,6 +37,42 @@ func TestTaskTextEventCursorPrefersQueryAndSupportsLastEventID(t *testing.T) {
 	}
 }
 
+func TestStreamTaskTextEventsCachedReplayReachesTerminalWithoutDuplicateDelta(t *testing.T) {
+	t.Setenv("REDIS_URL", "")
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.AutoMigrate(&model.Task{}, &model.TaskTextDelta{}); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Create(&model.Task{ID: "task", UserID: "user", Status: model.TaskStatusRunning}).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Create(&model.TaskTextDelta{ID: "delta", UserID: "user", TaskID: "task", Sequence: 8, Content: "text", ExpiresAt: time.Now().Add(time.Hour)}).Error; err != nil {
+		t.Fatal(err)
+	}
+	svc := service.New(repository.New(db), t.TempDir())
+	t.Cleanup(func() { _ = svc.Close() })
+	ctx, cancel := context.WithTimeout(context.Background(), 4*time.Second)
+	defer cancel()
+	initial, err := svc.CachedTaskTextReplay(ctx, "user", "task", 7)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Model(&model.Task{}).Where("id = ?", "task").Updates(map[string]any{"status": model.TaskStatusSucceeded, "progress": 100}).Error; err != nil {
+		t.Fatal(err)
+	}
+	response := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(response)
+	c.Request = httptest.NewRequest("GET", "/api/tasks/task/text-events", nil).WithContext(ctx)
+	streamTaskTextEvents(c, svc, "user", "task", 7, initial)
+	body := response.Body.String()
+	if strings.Count(body, "id: 8\nevent: delta") != 1 || !strings.Contains(body, "event: terminal") || !strings.Contains(body, `"progress":100`) {
+		t.Fatalf("unexpected cached SSE stream: %q", body)
+	}
+}
+
 func TestStreamTaskTextEventsWritesSequenceAndTerminalEvent(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	response := httptest.NewRecorder()