fix(migration): don't drop TickTick tasks sharing a malformed id

Collapsing unparseable taskIds to 0 meant sortParentsBeforeChildren,
which tracked placement by TaskID, treated every zero-id task after the
first as already placed and silently dropped it. Track placement by task
identity instead so duplicate or zero ids never conflate distinct tasks.

pkg/modules/migration/ticktick/ticktick.go

@@ -146,12 +146,16 @@ func sortParentsBeforeChildren(tasks []*tickTickTask) []*tickTickTask {
 		tasksByID[t.TaskID] = t
 	}
 
-	placed := make(map[tickTickNumber]bool, len(tasks))
+	// placed is keyed by the task itself rather than by TaskID: malformed
+	// exports can collapse several taskIds to 0 (see tickTickNumber), and
+	// keying by ID would treat every zero-ID task after the first as already
+	// placed and silently drop it.
+	placed := make(map[*tickTickTask]bool, len(tasks))
 	result := make([]*tickTickTask, 0, len(tasks))
 
 	var place func(t *tickTickTask)
 	place = func(t *tickTickTask) {
-		if placed[t.TaskID] {
+		if placed[t] {
 			return
 		}
 		// If this task has a parent that we know about, place the parent first.
@@ -160,7 +164,7 @@ func sortParentsBeforeChildren(tasks []*tickTickTask) []*tickTickTask {
 				place(parent)
 			}
 		}
-		placed[t.TaskID] = true
+		placed[t] = true
 		result = append(result, t)
 	}
 

pkg/modules/migration/ticktick/ticktick_test.go

@@ -846,3 +846,26 @@ func TestNonNumericNumberColumns(t *testing.T) {
 	}
 	assert.Equal(t, int64(1), priority)
 }
+
+// TestMultipleTasksWithMalformedIDsAreNotDropped guards against a regression
+// where collapsing several unparseable taskIds to 0 caused all but the first
+// zero-ID task to be silently dropped by sortParentsBeforeChildren.
+func TestMultipleTasksWithMalformedIDsAreNotDropped(t *testing.T) {
+	tasks := []*tickTickTask{
+		{TaskID: 0, ProjectName: "Project 1", Title: "First malformed"},
+		{TaskID: 0, ProjectName: "Project 1", Title: "Second malformed"},
+		{TaskID: 0, ProjectName: "Project 1", Title: "Third malformed"},
+	}
+
+	sorted := sortParentsBeforeChildren(tasks)
+	require.Len(t, sorted, 3, "no task with a zero ID should be dropped")
+
+	vikunjaTasks := convertTickTickToVikunja(tasks)
+	titles := []string{}
+	for _, project := range vikunjaTasks {
+		for _, task := range project.Tasks {
+			titles = append(titles, task.Title)
+		}
+	}
+	assert.ElementsMatch(t, []string{"First malformed", "Second malformed", "Third malformed"}, titles)
+}