fix(lua): 导出函数调用不标脏，插件状态从不落盘

quota 声明 hooks=[]，全部工作都在导出函数里。markDirty 只从 hook 与
SetState 触发，Call 两边都不占 —— 于是探测改的内存没人写盘，状态文件要等
下一次无关的配置写入才顺带刷新。

现象是「插件看起来没写」：负 memo 要等到下一次改配置才出现。用隔离实例
逐步观察时，一度把这误读成 memo 状态机的三个缺陷，逐个查清后只有这一条
是真的：

  - 「未就绪轮次累计 streak」 —— 不成立。写侧本来就对临时条目用 streak=1，
    65ed1b 版本已是这个行为。
  - 「读侧用旧快照，streak 永远停在 1」 —— 是退避的设计行为。单进程内第二
    次探测被退避挡在写侧之前，streak 自然不再增长；真实的多轮计数在跨进程
    （trace_streak.py）下是 1/2/3/4。
  - 「Call 不标脏」 —— 真缺陷，已验证：去掉 markDirtyLocked，
    新增的 TestOnDemandCallIsPersisted 立刻变红。

顺带保留两处无行为差异的可读性收紧：provisionalEntry 统一按「集合非空」
判断临时条目（与 copySet 空集返回 nil 的写法对齐）。

判据：TestOnDemandCallIsPersisted 用 hookless 插件走导出函数累加，
反向证明（去掉 markDirtyLocked）会红。

internal/lua/persist_test.go

@@ -281,3 +281,60 @@ func TestCloseFlushesTail(t *testing.T) {
 		t.Errorf("flushed n = %v, want 1", saved.State["n"])
 	}
 }
+
+// TestOnDemandCallIsPersisted guards the persistence gap that the quota memo fell
+// into, and it needs a plugin with NO hooks to see it.
+//
+// markDirty fired from two places: hooks and SetState. `Call` — the on-demand path
+// a plugin page uses — fired from neither, so a plugin that does all its work in
+// exported functions (quota: it declares no hooks at all) mutated state that
+// nothing ever wrote. The visible symptom was a health probe that looked inert
+// from outside: the memo changed in memory and the file kept the previous
+// generation until some unrelated configuration write happened to flush it.
+//
+// A hookless plugin is the whole point of the fixture: the counter above
+// accumulates through a hook, which is the path that already persisted, so it
+// cannot see this defect.
+func TestOnDemandCallIsPersisted(t *testing.T) {
+	ps, _ := newPersistVM(t)
+	if err := ps.LoadSource("ondemand", `
+local plugin = { name = "ondemand", version = "1.0" }
+plugin.state = { n = 0 }
+plugin.exports = { "bump" }
+function plugin.bump(payload)
+  plugin.state.n = plugin.state.n + 1
+  return { n = plugin.state.n }
+end
+return plugin
+`); err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 1; i <= 3; i++ {
+		out, err := ps.Call("ondemand", "bump", map[string]interface{}{})
+		if err != nil {
+			t.Fatalf("call %d: %v", i, err)
+		}
+		if m, _ := out.(map[string]interface{}); m["n"] != float64(i) {
+			t.Fatalf("call %d returned %v, want n=%d", i, out, i)
+		}
+	}
+	// Close() waits for the final flush, so no timing is involved: anything the
+	// calls did NOT mark dirty cannot appear here.
+	ps.Close()
+
+	b, err := os.ReadFile(ps.stateFile("ondemand"))
+	if err != nil {
+		t.Fatalf("★ an exported call did not mark the plugin dirty: %v — a plugin "+
+			"with no hooks can never persist its work", err)
+	}
+	var saved struct {
+		State map[string]interface{} `json:"state"`
+	}
+	if err := json.Unmarshal(b, &saved); err != nil {
+		t.Fatal(err)
+	}
+	if saved.State["n"] != float64(3) {
+		t.Errorf("persisted n = %v after three exported calls, want 3", saved.State["n"])
+	}
+}