feat: persist workflow signals and arbitrate poll completion

internal/storage/mysql/workflow_clock.go

@@ -14,7 +14,7 @@ import (
 // workflowCheckpoint 是待续表中版本化的内部唤醒身份；不保存内存执行栈或新的业务预算。
 type workflowCheckpoint struct {
 	SchemaVersion uint32   `json:"schema_version"`          // SchemaVersion 当前结构版本为1，未知版本禁止推进。
-	Kind          string   `json:"kind"`                    // Kind 为ROOT、TIMER或POLL，决定实际权威记录的读取方式。
+	Kind          string   `json:"kind"`                    // Kind 为ROOT、TIMER、SIGNAL或POLL，决定实际权威记录的读取方式。
 	ActivationID  *core.ID `json:"activation_id,omitempty"` // ActivationID 固定等待激活；ROOT不使用该字段。
 }
 
@@ -23,7 +23,7 @@ func saveWorkflowClock(ctx context.Context, tx *sql.Tx, g *workflowGraph, row *w
 	if err != nil {
 		return err
 	}
-	if row.view.ActivationID == nil || kind != "TIMER" && kind != "POLL" {
+	if row.view.ActivationID == nil || kind != "TIMER" && kind != "POLL" && kind != "SIGNAL" {
 		return errors.New("workflow clock identity invalid")
 	}
 	raw, err := json.Marshal(workflowCheckpoint{1, kind, row.view.ActivationID})
@@ -60,8 +60,24 @@ func (r *WorkflowRuntime) advanceClock(ctx context.Context, tx *sql.Tx, g *workf
 		return false, err
 	}
 	if checkpoint.Kind == "POLL" {
+		node, _ := g.program.Step(row.view.Key)
+		if node.Poll.FinalSignal != nil {
+			handled, changed, reason, err := r.driveWorkflowSignal(ctx, tx, g, row, c, nil, allow, now)
+			if err != nil {
+				return false, err
+			}
+			if handled {
+				if changed && reason != "" {
+					return true, r.audit(ctx, tx, g, c.id, reason, now)
+				}
+				return changed, nil
+			}
+		}
 		return r.advancePoll(ctx, tx, g, row, c, activated, allow, now)
 	}
+	if checkpoint.Kind == "SIGNAL" {
+		return r.advanceSignalClock(ctx, tx, g, row, c, allow, now)
+	}
 	if checkpoint.Kind != "TIMER" || row.view.State != weave.StepWaiting {
 		return false, errors.New("workflow timer state invalid")
 	}