feat: add durable safe retries with uncertainty tracking and SDK examples

sdk/go/worker_connection.go

@@ -332,6 +332,9 @@ func (w *WorkerConnection) Renew(ctx context.Context, id string, ref WorkerAttem
 // Finish 保存业务结果/证据；迟到结果可返回 EVIDENCE_ONLY，不能视为任务成功终结。
 func (w *WorkerConnection) Finish(ctx context.Context, id string, in WorkerFinish) (WorkerCommandResult, error) {
 	var out WorkerCommandResult
+	if in.Retryable && in.Outcome != WorkerFailed {
+		return out, errors.New("retryable is only valid for known failure")
+	}
 	if (in.Outcome != WorkerSucceeded && in.Outcome != WorkerFailed && in.Outcome != WorkerUnknown) || len(in.Result) > 256<<10 || bytes.Equal(bytes.TrimSpace(in.Result), []byte("null")) || validateWorkerJSON(in.Result) != nil {
 		return out, errors.New("invalid Worker result outcome or JSON")
 	}