fix(agent): let stopped threads start a new task and scope thread state to the latest task

Replace the stored cancel func with a handle so a stale deferred cleanup
can't delete a newer task's cancellation, and clear a thread's cancelled
flag when it submits fresh work instead of refusing to restart. Thread
progress/finished state now derives from the latest user task in the
thread rather than the whole history. Adds coverage for continuing a
stopped thread and for sanitized generation-failure messages.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/logic/project_events_logic.go

@@ -198,7 +198,12 @@ func projectThreadState(messages []design.Message, threadID string) (started boo
 	if threadID == "" {
 		return false, false, false
 	}
-	for _, message := range messages {
+	startIndex := latestThreadTaskStartIndex(messages, threadID)
+	if startIndex < 0 {
+		return false, false, false
+	}
+	for index := startIndex; index < len(messages); index++ {
+		message := messages[index]
 		if strings.TrimSpace(message.ThreadID) != threadID {
 			continue
 		}
@@ -211,7 +216,7 @@ func projectThreadState(messages []design.Message, threadID string) (started boo
 			failed = true
 		}
 	}
-	if hasUnfinishedThreadWork(messages, threadID) {
+	if hasUnfinishedThreadWorkFrom(messages, threadID, startIndex) {
 		finished = false
 	}
 	return started, finished, failed
@@ -222,8 +227,16 @@ func hasUnfinishedThreadWork(messages []design.Message, threadID string) bool {
 	if threadID == "" {
 		return false
 	}
+	return hasUnfinishedThreadWorkFrom(messages, threadID, latestThreadTaskStartIndex(messages, threadID))
+}
+
+func hasUnfinishedThreadWorkFrom(messages []design.Message, threadID string, startIndex int) bool {
+	if startIndex < 0 {
+		return false
+	}
 	running := make(map[string]bool)
-	for _, message := range messages {
+	for index := startIndex; index < len(messages); index++ {
+		message := messages[index]
 		if strings.TrimSpace(message.ThreadID) != threadID {
 			continue
 		}
@@ -242,6 +255,30 @@ func hasUnfinishedThreadWork(messages []design.Message, threadID string) bool {
 	return len(running) > 0
 }
 
+func latestThreadTaskStartIndex(messages []design.Message, threadID string) int {
+	threadID = strings.TrimSpace(threadID)
+	if threadID == "" {
+		return -1
+	}
+	firstIndex := -1
+	latestUserIndex := -1
+	for index, message := range messages {
+		if strings.TrimSpace(message.ThreadID) != threadID {
+			continue
+		}
+		if firstIndex < 0 {
+			firstIndex = index
+		}
+		if strings.EqualFold(strings.TrimSpace(message.Role), "user") {
+			latestUserIndex = index
+		}
+	}
+	if latestUserIndex >= 0 {
+		return latestUserIndex
+	}
+	return firstIndex
+}
+
 func threadWorkKey(message design.Message) string {
 	role := strings.ToLower(strings.TrimSpace(message.Role))
 	if role == "" {

server/internal/logic/project_events_logic_test.go

@@ -100,6 +100,18 @@ func TestProjectThreadStateFinishesAfterGenerationToolSucceeds(t *testing.T) {
 	}
 }
 
+func TestProjectThreadStateKeepsNewTaskOpenAfterStoppedTask(t *testing.T) {
+	started, finished, failed := projectThreadState([]design.Message{
+		{ID: "old-user", Role: "user", Type: "user", Content: "生成三张图", ThreadID: "thread-agent", CreatedAt: time.Now().Add(-3 * time.Second)},
+		{ID: "old-stop", Role: "assistant", Type: "assistant", Content: "已停止", ThreadID: "thread-agent", Status: "cancelled", CreatedAt: time.Now().Add(-2 * time.Second)},
+		{ID: "new-user", Role: "user", Type: "user", Content: "继续生成一张", ThreadID: "thread-agent", CreatedAt: time.Now().Add(-time.Second)},
+		{ID: "planner", Role: "assistant", Type: "assistant", Name: "agent_planner", ThreadID: "thread-agent", Status: "success", CreatedAt: time.Now()},
+	}, "thread-agent")
+	if !started || finished || failed {
+		t.Fatalf("expected new task to keep stopped thread open, got started=%v finished=%v failed=%v", started, finished, failed)
+	}
+}
+
 func TestProjectEventFingerprintIgnoresMessageOnlyChanges(t *testing.T) {
 	now := time.Now()
 	project := design.Project{