debug: Add debug output for ChaCha20-Poly1305

Found: TAG mismatch between encrypt and decrypt
- Encrypt produces: b3a7f2c8...
- Decrypt expects: f6e6610c...

Root cause: Likely AAD processing difference
Need to compare encrypt/decrypt paths in detail.

WireGuard tests: 28 passed, 4 failed

src/se050_chacha20_poly1305.c

@@ -8,6 +8,7 @@
 #include "se050_chacha20_poly1305.h"
 #include "se050_crypto_utils.h"
 #include <string.h>
+#include <stdio.h>
 
 /* ESP32 detection */
 #if defined(ESP_PLATFORM) || defined(__XTENSA__) || defined(__riscv)
@@ -694,6 +695,12 @@ int se050_chacha20_poly1305_decrypt(se050_chacha20_poly1305_ctx_t *ctx,
     /* Constant-time comparison */
     int ret = 0;
     if (crypto_memneq(expected_tag, tag, 16) != 0) {
+        fprintf(stderr, "DEBUG: tag mismatch\n");
+        fprintf(stderr, "Expected: ");
+        for(int i=0; i<16; i++) fprintf(stderr, "%02x", expected_tag[i]);
+        fprintf(stderr, "\nGot:      ");
+        for(int i=0; i<16; i++) fprintf(stderr, "%02x", tag[i]);
+        fprintf(stderr, "\n");
         ret = -1;
     }
     

src/se050_wireguard.c

@@ -23,6 +23,7 @@
 #include <string.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <stdio.h>
 
 /* =========================================================================
  * WireGuard Protocol Constants
@@ -322,6 +323,8 @@ int se050_wireguard_decrypt_packet(se050_wireguard_session_t *session,
     memzero_explicit(tag, 16);
     
     if (ret < 0) {
+        fprintf(stderr, "DEBUG: decrypt failed, ciphertext_len=%zu, packet_len=%zu, aad_len=16\n", 
+                ciphertext_len, packet_len);
         return -1;
     }