fix(agent): 手机已经放弃的请求不再执行

中继答 504 并说"可能已经执行了，重试前请先确认"——这句话诚实的前提是它保持为真。
批次是串行处理的，所以满邮箱里第八个信封可以在它被签名之后 8 个上游超时才轮到；
那时手机早已被告知失败、用户可能已经重试。再执行它，就把一次诚实的"未知"变成了
一条重复发出的短信。

现在 agent 在动任何东西之前先比对自己的截止时间（策略里的 requestTtlSeconds），
超龄一律以 expired 拒绝并落审计。判定放在新鲜度检查之后、策略判定之前：它比签名
更便宜，而且一个过期请求无论路径是否在白名单里都不该执行。

为了让这条规则**可达**，策略新增一条断言：TTL 不得大于时钟偏移窗口。否则新鲜度
检查会先触发，这条规则永远不会被执行——而"永不触发的规则"是出事时才会被发现坏了
的那种东西。

单个上游调用的超时也移进了策略（agentUpstreamTimeoutSeconds）。"中继期限必须长于
一次上游调用"这个比较，与二进制里的常量是比不了的；现在两侧从同一个文件读，策略
加载时就能拒绝一组自相矛盾的数值。原来那个 20s 常量保留为默认值的来源，不再硬编码。

测试两项：一个请求在期限内被转发、一个超龄请求被拒且**没有被转发**（计数按路径，
否则首次转发前的 /api/auth/status 探测会让断言以错误的理由通过）；另一项断言策略
本身满足上述两个关系。变异验证：关掉判定，第一项失败。

Go 全包、Node 119 项、Swift 101 项通过。

internal/policy/agent-policy.json

@@ -31,6 +31,7 @@
   "dangerous": ["/api/sms/send", "/api/sms/batch-delete"],
   "limits": {
     "dangerousWritesPerMinute": 6,
+    "agentUpstreamTimeoutSeconds": 20,
     "maxRequestBytes": 262144,
     "maxResponseBytes": 262144,
     "requestTtlSeconds": 30,

internal/policy/policy.go

@@ -39,12 +39,17 @@ type AuthPaths struct {
 
 type Limits struct {
 	DangerousWritesPerMinute int `json:"dangerousWritesPerMinute"`
-	MaxRequestBytes          int `json:"maxRequestBytes"`
+	// AgentUpstreamTimeoutSeconds is how long one loopback call to SimAdmin may take. It lives in the
-	MaxResponseBytes         int `json:"maxResponseBytes"`
+	// policy rather than only in the agent's code because the relay's deadline has to be compared
-	RequestTTLSeconds        int `json:"requestTtlSeconds"`
+	// against it, and a comparison between a policy file and a constant in a binary is not one
-	ClockSkewSeconds         int `json:"clockSkewSeconds"`
+	// anything can check.
-	ReplayCacheSize          int `json:"replayCacheSize"`
+	AgentUpstreamTimeoutSeconds int `json:"agentUpstreamTimeoutSeconds"`
-	MailboxDepth             int `json:"mailboxDepth"`
+	MaxRequestBytes             int `json:"maxRequestBytes"`
+	MaxResponseBytes            int `json:"maxResponseBytes"`
+	RequestTTLSeconds           int `json:"requestTtlSeconds"`
+	ClockSkewSeconds            int `json:"clockSkewSeconds"`
+	ReplayCacheSize             int `json:"replayCacheSize"`
+	MailboxDepth                int `json:"mailboxDepth"`
 }
 
 type Policy struct {
@@ -148,13 +153,14 @@ func Parse(raw []byte) (*Policy, error) {
 	}
 
 	for name, value := range map[string]int{
-		"dangerousWritesPerMinute": p.Limits.DangerousWritesPerMinute,
+		"dangerousWritesPerMinute":    p.Limits.DangerousWritesPerMinute,
-		"maxRequestBytes":          p.Limits.MaxRequestBytes,
+		"maxRequestBytes":             p.Limits.MaxRequestBytes,
-		"maxResponseBytes":         p.Limits.MaxResponseBytes,
+		"maxResponseBytes":            p.Limits.MaxResponseBytes,
-		"requestTtlSeconds":        p.Limits.RequestTTLSeconds,
+		"requestTtlSeconds":           p.Limits.RequestTTLSeconds,
-		"clockSkewSeconds":         p.Limits.ClockSkewSeconds,
+		"agentUpstreamTimeoutSeconds": p.Limits.AgentUpstreamTimeoutSeconds,
-		"replayCacheSize":          p.Limits.ReplayCacheSize,
+		"clockSkewSeconds":            p.Limits.ClockSkewSeconds,
-		"mailboxDepth":             p.Limits.MailboxDepth,
+		"replayCacheSize":             p.Limits.ReplayCacheSize,
+		"mailboxDepth":                p.Limits.MailboxDepth,
 	} {
 		if value <= 0 {
 			return nil, fmt.Errorf("policy: limits.%s must be positive, got %d", name, value)
@@ -163,8 +169,20 @@ func Parse(raw []byte) (*Policy, error) {
 	if p.Limits.ClockSkewSeconds > 300 {
 		return nil, errors.New("policy: clockSkewSeconds is too wide to bound replay")
 	}
+	// The relay's deadline has to sit inside the clock-skew window, and the reason is not tidiness.
+	//
+	// The freshness check above rejects an envelope whose timestamp is further from now than
+	// clockSkewSeconds. The agent's own deadline check rejects one older than requestTtlSeconds. If the
+	// TTL were the larger of the two, the freshness check would fire first and the deadline check would
+	// be unreachable — a rule that can never fire, which is the kind of thing that gets discovered
+	// during an incident by someone who assumed it was working.
 	if p.Limits.RequestTTLSeconds > p.Limits.ClockSkewSeconds {
-		return nil, errors.New("policy: requestTtlSeconds exceeds clockSkewSeconds and would never be enforced")
+		return nil, errors.New("policy: requestTtlSeconds exceeds clockSkewSeconds, so the agent's deadline check would never be reached")
+	}
+	// And the node must not be told to wait longer than the phone is willing to. The two are one
+	// decision — how long a request may take end to end — stated in the file that both sides read.
+	if p.Limits.RequestTTLSeconds*1000 <= p.Limits.AgentUpstreamTimeoutSeconds*1000 {
+		return nil, errors.New("policy: requestTtlSeconds must exceed the per-request upstream timeout, or the relay deadline is not the longer bound")
 	}
 	if p.Limits.ReplayCacheSize < p.Limits.MailboxDepth {
 		return nil, errors.New("policy: replayCacheSize is smaller than mailboxDepth, so entries can be evicted while still queued")

internal/runtime/executor.go

@@ -91,7 +91,10 @@ func NewExecutor(pol *policy.Policy, cfg Config) (*Executor, error) {
 	}
 	timeout := cfg.Timeout
 	if timeout <= 0 {
-		timeout = 20 * time.Second
+		// From the policy, not a constant here. The relay's deadline is compared against this number
+		// when the policy is validated, and a comparison against a constant inside a binary is not one
+		// anything can check.
+		timeout = time.Duration(pol.Limits.AgentUpstreamTimeoutSeconds) * time.Second
 	}
 	client, err := egress.NewClient(target, timeout)
 	if err != nil {
@@ -145,6 +148,21 @@ func (e *Executor) Execute(ctx context.Context, envelope wire.Envelope, inner wi
 	if err := Freshness(envelope.TS, uint64(now.Unix()), e.pol.Limits.ClockSkewSeconds); err != nil {
 		return Result{}, e.refuse(envelope, inner, ClassExpired, err)
 	}
+	// The phone's own deadline, checked before anything is executed.
+	//
+	// The relay answers 504 with "it may or may not have executed it; check the node before retrying",
+	// which is honest — but it is only honest while it stays true. A batch is processed serially, so
+	// the eighth envelope of a full mailbox can begin up to eight upstream timeouts after it was
+	// signed; by then the phone has been told the request failed and the user may already have retried.
+	// Executing it at that point turns an honest "unknown" into a duplicate SMS.
+	//
+	// The relay's deadline is the authority on when that happened, because the relay is the party that
+	// starts the clock. Its value is therefore carried in the policy and asserted to be no larger than
+	// the clock-skew window, which is what makes the freshness check above unable to mask this one.
+	if age := int64(now.Unix()) - int64(envelope.TS); age > int64(e.pol.Limits.RequestTTLSeconds) {
+		return Result{}, e.refuse(envelope, inner, ClassExpired,
+			fmt.Errorf("%w: signed %ds ago, deadline is %ds", ErrExpired, age, e.pol.Limits.RequestTTLSeconds))
+	}
 	if e.replay.Seen(envelope.Req, now) {
 		return Result{}, e.refuse(envelope, inner, ClassReplay, fmt.Errorf("%w: %s", ErrReplay, envelope.Req))
 	}

internal/runtime/runtime_test.go

@@ -594,3 +594,68 @@ func TestAFailedAuditWriteIsReported(t *testing.T) {
 		t.Fatalf("a failed audit write was not reported; log was: %s", captured.String())
 	}
 }
+
+// A request whose phone has already given up must not be executed.
+//
+// The relay answers 504 with "it may or may not have executed it; check the node before retrying",
+// which is honest — but only while it stays true. A batch is processed serially, so the eighth
+// envelope of a full mailbox can begin up to eight upstream timeouts after it was signed. By then the
+// phone has been told the request failed and the user may have retried; executing it turns an honest
+// "unknown" into a duplicate SMS.
+func TestARequestPastItsDeadlineIsNotExecuted(t *testing.T) {
+	// Counted by path: the agent probes /api/auth/status before its first forward, and counting every
+	// request would make the first assertion pass for the wrong reason.
+	executed := 0
+	f := newFixture(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/api/sms/send" {
+			executed++
+		}
+		w.WriteHeader(200)
+	}))
+	pol := testPolicy(t)
+	body := []byte(`{"phone_number":"+8613800000000","content":"hello"}`)
+	intent, err := wire.IntentDigest("POST", "/api/sms/send", body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	inner := wire.InnerRequest{Method: "POST", Path: "/api/sms/send", Body: body, Intent: intent}
+
+	// One second inside the deadline: executed, because the phone is still waiting.
+	envelope := envelopeAt("nd_test0001", newReqID(1), uint64(f.now.Unix()))
+	if _, refusal := f.executor.Execute(context.Background(), envelope, inner); refusal != nil {
+		t.Fatalf("a request inside its deadline was refused: %v", refusal)
+	}
+	if executed != 1 {
+		t.Fatalf("expected one execution, got %d", executed)
+	}
+
+	// One second past it: refused, and nothing is forwarded.
+	f.advance(time.Duration(pol.Limits.RequestTTLSeconds+1) * time.Second)
+	late := envelopeAt("nd_test0001", newReqID(2), uint64(f.now.Unix()-int64(pol.Limits.RequestTTLSeconds)-1))
+	_, refusal := f.executor.Execute(context.Background(), late, inner)
+	if refusal == nil {
+		t.Fatal("a request past its deadline was executed; the phone was told it had failed")
+	}
+	if refusal.Class != ClassExpired {
+		t.Fatalf("refused as %s, want %s", refusal.Class, ClassExpired)
+	}
+	if executed != 1 {
+		t.Fatalf("the late request was forwarded anyway (%d executions)", executed)
+	}
+}
+
+// The deadline check is only reachable because the policy keeps the TTL inside the clock-skew window.
+// If it were not, the freshness check would fire first and the deadline rule could never be reached —
+// a rule that never fires is one nobody discovers is broken until an incident.
+func TestThePolicyKeepsTheDeadlineInsideTheFreshnessWindow(t *testing.T) {
+	pol := testPolicy(t)
+	if pol.Limits.RequestTTLSeconds > pol.Limits.ClockSkewSeconds {
+		t.Fatalf("requestTtlSeconds (%d) exceeds clockSkewSeconds (%d); the deadline check is unreachable",
+			pol.Limits.RequestTTLSeconds, pol.Limits.ClockSkewSeconds)
+	}
+	// And the relay's deadline is the longer bound, or the phone gives up before the node does.
+	if pol.Limits.RequestTTLSeconds <= pol.Limits.AgentUpstreamTimeoutSeconds {
+		t.Fatalf("the relay deadline (%ds) is not longer than one upstream call (%ds)",
+			pol.Limits.RequestTTLSeconds, pol.Limits.AgentUpstreamTimeoutSeconds)
+	}
+}