diff --git a/service/error_memory.go b/service/error_memory.go
new file mode 100644
index 0000000..86b215d
--- /dev/null
+++ b/service/error_memory.go
@@ -0,0 +1,43 @@
+package service
+
+import (
+	"crypto/md5"
+	"crypto/sha256"
+	"encoding/hex"
+	"regexp"
+	"strings"
+)
+
+var (
+	reUUID      = regexp.MustCompile(`[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}`)
+	reISOTime   = regexp.MustCompile(`\d{4}-\d{2}-\d{2}[T ]\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:?\d{2})?`)
+	reUnixMs    = regexp.MustCompile(`\b1[4-9]\d{12}\b`)                     // unix 毫秒级时间戳
+	reRequestID = regexp.MustCompile(`\b(req[-_]?|request[-_]?|rid[-_:]?)[-_:]?[0-9a-zA-Z-]{4,}\b`)
+	reLongNum   = regexp.MustCompile(`\b\d{4,}\b`)                           // 连续≥4位数字
+)
+
+// normalizeErrorMsg 归一化错误消息：剔除易变片段（UUID/时间戳/请求ID/连续数字），
+// 使同因不同实例的错误命中同一记忆键。
+func normalizeErrorMsg(msg string) string {
+	m := msg
+	m = reUUID.ReplaceAllString(m, "{uuid}")
+	m = reISOTime.ReplaceAllString(m, "{time}")
+	m = reUnixMs.ReplaceAllString(m, "{ts}")
+	m = reRequestID.ReplaceAllString(m, "{reqid}")
+	m = reLongNum.ReplaceAllString(m, "{num}")
+	return strings.TrimSpace(m)
+}
+
+// buildMemoryKey 构造记忆键 = SHA-256(upstream|error_code|归一化消息)。
+// 含失败上游维度：不同上游的同类错误互不串扰。
+func buildMemoryKey(upstream, code, msg string) string {
+	raw := strings.Join([]string{upstream, code, normalizeErrorMsg(msg)}, "|")
+	sum := sha256.Sum256([]byte(raw))
+	return hex.EncodeToString(sum[:])
+}
+
+// msgFingerprint 归一化消息的 md5（观测/展示用）。
+func msgFingerprint(msg string) string {
+	sum := md5.Sum([]byte(normalizeErrorMsg(msg)))
+	return hex.EncodeToString(sum[:])
+}
diff --git a/service/error_memory_test.go b/service/error_memory_test.go
new file mode 100644
index 0000000..947bd2e
--- /dev/null
+++ b/service/error_memory_test.go
@@ -0,0 +1,43 @@
+package service
+
+import "testing"
+
+func TestNormalizeErrorMsg(t *testing.T) {
+	cases := []struct{ in, want string }{
+		{"rate limit exceeded for req-abc123", "rate limit exceeded for {reqid}"},
+		{"timeout at 2026-09-01T09:00:00Z req_88f1a2", "timeout at {time} {reqid}"},
+		{"uuid 0f8fad5b-d9cb-469f-a165-70867728950e remains", "uuid {uuid} remains"},
+		{"err code 12345678 quota exceeded", "err code {num} quota exceeded"},
+		{"clean message unchanged", "clean message unchanged"},
+	}
+	for _, c := range cases {
+		if got := normalizeErrorMsg(c.in); got != c.want {
+			t.Fatalf("normalizeErrorMsg(%q) = %q, want %q", c.in, got, c.want)
+		}
+	}
+}
+
+func TestBuildMemoryKey(t *testing.T) {
+	k1 := buildMemoryKey("https://a.com", "429", "rate limit for req-a1b2c3")
+	k2 := buildMemoryKey("https://a.com", "429", "rate limit for req-d4e5f6") // 同因不同请求ID
+	if k1 != k2 {
+		t.Fatalf("同因不同请求ID应同键: %s != %s", k1, k2)
+	}
+	k3 := buildMemoryKey("https://b.com", "429", "rate limit for req-a1b2c3") // 不同上游
+	if k1 == k3 {
+		t.Fatalf("不同上游应不同键")
+	}
+	k4 := buildMemoryKey("https://a.com", "500", "rate limit for req-a1b2c3") // 不同错误码
+	if k1 == k4 {
+		t.Fatalf("不同错误码应不同键")
+	}
+	if len(k1) != 64 {
+		t.Fatalf("memory_key 应为 SHA-256 十六进制64位, got %d", len(k1))
+	}
+}
+
+func TestMsgFingerprint(t *testing.T) {
+	if msgFingerprint("a req-a1b2c3") != msgFingerprint("a req-d4e5f6") {
+		t.Fatalf("同因指纹应一致")
+	}
+}