Avoid duplicating the ECH config in short payload test

The hard-coded short-payload ClientHello only needs the configured ECH identifier, KEM, and HPKE cipher to match in order to exercise the intended server opener path. Parse ECH_CONFIG_LIST and assert those fields instead of carrying a second full byte copy of the config.

Co-authored-by: Codex <codex@openai.com>

t/picotls.c

diff --git a/t/picotls.c b/t/picotls.c
index bb7ce37..41adb66 100644
--- a/t/picotls.c
+++ b/t/picotls.c
@@ -1748,13 +1748,6 @@
 {
     /* This ClientHello is tied to ECH_CONFIG_LIST and the matching ECH_PRIVATE_KEY from t/test.h. The HPKE enc value is valid for
      * that key and config, which lets the server create the ECH AEAD context before it rejects the one-byte ECH payload. */
-    static const uint8_t expected_ech_config_list[] = {
-        0x00, 0x63, 0xfe, 0x0d, 0x00, 0x5f, 0x12, 0x00, 0x10, 0x00, 0x41, 0x04, 0xfe, 0x8c, 0x19, 0xce, 0x09,
-        0x05, 0x19, 0x1e, 0xbc, 0x29, 0x8a, 0x92, 0x45, 0x79, 0x25, 0x31, 0xf2, 0x6f, 0x0c, 0xec, 0xe2, 0x46,
-        0x06, 0x39, 0xe8, 0xbc, 0x39, 0xcb, 0x7f, 0x70, 0x6a, 0x82, 0x6a, 0x77, 0x9b, 0x4c, 0xf9, 0x69, 0xb8,
-        0xa0, 0xe5, 0x39, 0xc7, 0xf6, 0x2f, 0xb3, 0xd3, 0x0a, 0xd6, 0xaa, 0x8f, 0x80, 0xe3, 0x0f, 0x1d, 0x12,
-        0x8a, 0xaf, 0xd6, 0x8a, 0x2c, 0xe7, 0x2e, 0xa0, 0x00, 0x08, 0x00, 0x02, 0x00, 0x02, 0x00, 0x01, 0x00,
-        0x01, 0x40, 0x0b, 0x65, 0x78, 0x61, 0x6d, 0x70, 0x6c, 0x65, 0x2e, 0x63, 0x6f, 0x6d, 0x00, 0x00};
     static const uint8_t ch[] = {
         0x16, 0x03, 0x03, 0x01, 0x03, 0x01, 0x00, 0x00, 0xff, 0x03, 0x03, 0x6d, 0x64, 0xb4, 0x65, 0x77, 0xf2,
         0xdd, 0x12, 0x97, 0xbe, 0x68, 0x53, 0x75, 0x3b, 0x27, 0x2f, 0xc9, 0xdc, 0x08, 0x3b, 0xa4, 0x7b, 0x93,
@@ -1772,14 +1765,19 @@
         0x78, 0x61, 0x6d, 0x70, 0x6c, 0x65, 0x2e, 0x63, 0x6f, 0x6d, 0x00, 0x2b, 0x00, 0x03, 0x02, 0x03, 0x04,
         0x00, 0x0d, 0x00, 0x0e, 0x00, 0x0c, 0x08, 0x05, 0x08, 0x04, 0x05, 0x03, 0x04, 0x03, 0x04, 0x01, 0x02,
         0x01, 0x00, 0x0a, 0x00, 0x04, 0x00, 0x02, 0x00, 0x17};
+    struct st_decoded_ech_config_t decoded;
     ptls_t *server;
     ptls_buffer_t sbuf;
     size_t consumed;
     int ret;
 
     ok(ctx_peer->ech.server.create_opener != NULL);
-    ok(sizeof(ECH_CONFIG_LIST) - 1 == sizeof(expected_ech_config_list));
-    ok(memcmp(ECH_CONFIG_LIST, expected_ech_config_list, sizeof(expected_ech_config_list)) == 0);
+    ret = client_decode_ech_config_list(ctx_peer, &decoded, ptls_iovec_init(ECH_CONFIG_LIST, sizeof(ECH_CONFIG_LIST) - 1));
+    ok(ret == 0);
+    ok(decoded.id == 0x12);
+    ok(decoded.kem != NULL && decoded.kem->id == PTLS_HPKE_KEM_P256_SHA256);
+    ok(decoded.cipher != NULL && decoded.cipher->id.kdf == PTLS_HPKE_HKDF_SHA384 &&
+       decoded.cipher->id.aead == PTLS_HPKE_AEAD_AES_256_GCM);
 
     server = ptls_new(ctx_peer, 1);
     ptls_buffer_init(&sbuf, "", 0);