feat(weixin_ilink): 出站媒体走通（主人已批的三项）

按官方包 @tencent-weixin/openclaw-weixin 2.4.9 源码对齐：
① 上传由 PUT 改 POST；② 上传凭据读响应头 x-encrypted-param；
③ nativeMediaItem 改为官方 *_item.media.encrypt_query_param 嵌套形状（含 aes_key，
图片优先 image_item.aeskey）。
配合前一版已修的两点（入站按条密钥、媒体失败不阻断文本），机器人现在可主动发出文件/图片。
（逐项测试、变异红行与诚实边界见该切片报告）

plugins/channels/weixin_ilink/send_test.go

@@ -3,8 +3,6 @@ package weixin_ilink
 import (
 	"bytes"
 	"context"
-	"crypto/aes"
-	"encoding/base64"
 	"errors"
 	"net/http"
 	"net/http/httptest"
@@ -146,6 +144,8 @@ func TestSendProactive_NoPriorInbound(t *testing.T) {
 	}
 }
 
+// TestSendMessage_OutboundMedia 走通一整条出站媒体链：getuploadurl → CDN 上传（POST +
+// `x-encrypted-param`）→ 按官方嵌套形状组装 item → sendmessage。
 func TestSendMessage_OutboundMedia(t *testing.T) {
 	t.Parallel()
 	rec := &reqRecorder{}
@@ -153,13 +153,17 @@ func TestSendMessage_OutboundMedia(t *testing.T) {
 	srv = newJSONServer(t, rec, func(req recordedReq) handlerResult {
 		switch {
 		case req.method == http.MethodPost && req.path == "/ilink/bot/getuploadurl":
-			return handlerResult{body: jsonBody(map[string]any{"upload_url": srv.URL + "/upload/1"})}
-		case req.method == http.MethodPut && req.path == "/upload/1":
-			return handlerResult{status: 200, body: []byte("ok")}
+			return handlerResult{body: jsonBody(map[string]any{"upload_full_url": srv.URL + "/cdn/up"})}
+		case req.method == http.MethodPost && req.path == "/cdn/up":
+			return handlerResult{
+				status:  http.StatusOK,
+				body:    []byte("ok"),
+				headers: map[string]string{uploadParamHeader: downloadParamFixture},
+			}
 		case req.method == http.MethodPost && req.path == "/ilink/bot/sendmessage":
 			return handlerResult{body: jsonBody(map[string]any{"ret": 0})}
 		default:
-			return handlerResult{status: 404}
+			return handlerResult{status: http.StatusNotFound}
 		}
 	})
 
@@ -183,27 +187,29 @@ func TestSendMessage_OutboundMedia(t *testing.T) {
 	if typ, ok := item["type"].(float64); !ok || typ != 2 {
 		t.Fatalf("media item type = %v, want 2", item["type"])
 	}
-	if item["cdn_ref"] != srv.URL+"/upload/1" {
-		t.Fatalf("cdn_ref = %v, want upload url", item["cdn_ref"])
+	imageItem, ok := item["image_item"].(map[string]any)
+	if !ok {
+		t.Fatalf("item 不是官方的 image_item 嵌套形状：%+v", item)
 	}
-	aesKeyEncoded, _ := item["aes_key"].(string)
-	if aesKeyEncoded == "" {
-		t.Fatal("aes_key missing on media item")
+	media := imageItem["media"].(map[string]any)
+	if media["encrypt_query_param"] != downloadParamFixture {
+		t.Fatalf("encrypt_query_param = %v, want 上传响应头带回来的凭据 %q",
+			media["encrypt_query_param"], downloadParamFixture)
 	}
-	key, err := base64.StdEncoding.DecodeString(aesKeyEncoded)
+	key, err := parseMediaAesKey(media["aes_key"].(string))
 	if err != nil {
-		t.Fatalf("decode aes_key: %v", err)
-	}
-	if len(key) != aes.BlockSize {
-		t.Fatalf("aes_key = %d bytes, want %d", len(key), aes.BlockSize)
+		t.Fatalf("解 item 上的 aes_key: %v", err)
 	}
 
-	// 已上传的字节（PUT 请求体）必须能解密回原始媒体。
-	puts := rec.find(func(q recordedReq) bool { return q.method == http.MethodPut })
-	if len(puts) != 1 {
-		t.Fatalf("PUT requests = %d, want 1", len(puts))
+	// 已上传的字节（POST 请求体）必须能解密回原始媒体。
+	posts := rec.find(func(q recordedReq) bool { return q.path == "/cdn/up" })
+	if len(posts) != 1 {
+		t.Fatalf("CDN 上传请求 = %d 次, want 1", len(posts))
 	}
-	decrypted, err := aesECBDecrypt(key, puts[0].body)
+	if posts[0].method != http.MethodPost {
+		t.Fatalf("上传方法 = %s, want POST（官方口径）", posts[0].method)
+	}
+	decrypted, err := aesECBDecrypt(key, posts[0].body)
 	if err != nil {
 		t.Fatalf("decrypt uploaded media: %v", err)
 	}