Return step logs strictly in line order (#6999)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>

server/store/datastore/log.go

@@ -27,9 +27,11 @@ import (
 // Too large a value results in `pq: got XX parameters but PostgreSQL only supports 65535 parameters`.
 const pgBatchSize = 1000
 
+// LogFind returns the log entries of a step in the order the agent produced
+// them, which is the order their line numbers carry.
 func (s storage) LogFind(step *model.Step) ([]*model.LogEntry, error) {
 	var logEntries []*model.LogEntry
-	return logEntries, s.engine.Asc("id").Where("step_id = ?", step.ID).Find(&logEntries)
+	return logEntries, s.engine.Asc("line").Where("step_id = ?", step.ID).Find(&logEntries)
 }
 
 func (s storage) LogAppend(_ *model.Step, logEntries []*model.LogEntry) error {

server/store/datastore/log_test.go

@@ -96,3 +96,36 @@ func TestLogAppend(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Len(t, _logEntries, len(logEntries)+1)
 }
+
+func TestLogFindOrdersByLine(t *testing.T) {
+	store, closer := newTestStore(t, new(model.Step), new(model.LogEntry))
+	defer closer()
+
+	step := model.Step{
+		ID: 1,
+	}
+
+	// The first batch is written through a node holding the id cache 4000+,
+	// the second one through a node holding the lower cache 30+.
+	assert.NoError(t, store.LogAppend(&step, []*model.LogEntry{
+		{ID: 4000, StepID: step.ID, Data: []byte("first"), Line: 0, Time: 0},
+		{ID: 4001, StepID: step.ID, Data: []byte("second"), Line: 1, Time: 10},
+	}))
+	assert.NoError(t, store.LogAppend(&step, []*model.LogEntry{
+		{ID: 30, StepID: step.ID, Data: []byte("third"), Line: 2, Time: 20},
+		{ID: 31, StepID: step.ID, Data: []byte("fourth"), Line: 3, Time: 30},
+	}))
+
+	logEntries, err := store.LogFind(&step)
+	assert.NoError(t, err)
+
+	lines := make([]int, 0, len(logEntries))
+	data := make([]string, 0, len(logEntries))
+	for _, logEntry := range logEntries {
+		lines = append(lines, logEntry.Line)
+		data = append(data, string(logEntry.Data))
+	}
+
+	assert.Equal(t, []int{0, 1, 2, 3}, lines)
+	assert.Equal(t, []string{"first", "second", "third", "fourth"}, data)
+}