fix(canvas): 文本生成 - 修复分镜超时并贯通 Agent 与创作页流式返回

backend/internal/service/task_text_stream.go

@@ -0,0 +1,84 @@
+package service
+
+import (
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	taskTextStreamFlushBytes    = 2 << 10
+	taskTextStreamFlushInterval = 500 * time.Millisecond
+)
+
+// taskTextStreamPublisher batches model deltas before persisting them. Streaming
+// is an observability and recovery enhancement: persistence failure must not turn
+// an otherwise successful model response into a failed generation task.
+type taskTextStreamPublisher struct {
+	service  *Service
+	userID   string
+	taskID   string
+	mu       sync.Mutex
+	buffer   strings.Builder
+	timer    *time.Timer
+	disabled bool
+	closed   bool
+}
+
+func newTaskTextStreamPublisher(service *Service, userID string, taskID string) *taskTextStreamPublisher {
+	return &taskTextStreamPublisher{service: service, userID: userID, taskID: taskID}
+}
+
+func (p *taskTextStreamPublisher) Publish(delta string) {
+	if p == nil || delta == "" {
+		return
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.disabled || p.closed {
+		return
+	}
+	p.buffer.WriteString(delta)
+	if p.buffer.Len() >= taskTextStreamFlushBytes {
+		p.flushLocked()
+		return
+	}
+	if p.timer == nil {
+		p.timer = time.AfterFunc(taskTextStreamFlushInterval, p.flush)
+	}
+}
+
+func (p *taskTextStreamPublisher) Close() {
+	if p == nil {
+		return
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.closed = true
+	p.flushLocked()
+}
+
+func (p *taskTextStreamPublisher) flush() {
+	if p == nil {
+		return
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.flushLocked()
+}
+
+func (p *taskTextStreamPublisher) flushLocked() {
+	if p.timer != nil {
+		p.timer.Stop()
+		p.timer = nil
+	}
+	if p.disabled || p.buffer.Len() == 0 {
+		return
+	}
+	content := p.buffer.String()
+	p.buffer.Reset()
+	if _, err := p.service.AppendTaskTextDelta(p.userID, p.taskID, content); err != nil {
+		p.disabled = true
+		_ = p.service.log(p.userID, p.taskID, "warn", "文本流持久化已降级", err.Error())
+	}
+}