msg b64: base64-encode display prefix in d-field to avoid pipe/quote breaking parse

b64_encode/decode (URL-safe A-Za-z0-9-_) in chat_core_priv.h
on_media_registered encodes msg_data before full_data
on_msg_inserted/chat_core_attachment_download decode base_filename
android_jni_bridge decodes prefix for UI display

src/chat/chat_core_priv.h

@@ -16,9 +16,63 @@
 #include <sqlite3.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdint.h>
 
 #define CC_ID "chat_core"
 
+/* ── Base64 encode/decode (URL-safe, used for msg "d" field prefix) ── */
+
+static const char B64_ALPHABET[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+static inline int b64_decode_char(char c) {
+    if (c >= 'A' && c <= 'Z') return c - 'A';
+    if (c >= 'a' && c <= 'z') return c - 'a' + 26;
+    if (c >= '0' && c <= '9') return c - '0' + 52;
+    if (c == '-') return 62;
+    if (c == '_') return 63;
+    return -1;
+}
+
+static inline size_t b64_encode(const uint8_t* src, size_t src_len, char* dst, size_t dst_cap) {
+    size_t out = 0;
+    for (size_t i = 0; i < src_len; i += 3) {
+        if (out + 4 > dst_cap) break;
+        uint32_t v = (uint32_t)src[i] << 16;
+        if (i + 1 < src_len) v |= (uint32_t)src[i + 1] << 8;
+        if (i + 2 < src_len) v |= (uint32_t)src[i + 2];
+        dst[out++] = B64_ALPHABET[(v >> 18) & 0x3F];
+        dst[out++] = B64_ALPHABET[(v >> 12) & 0x3F];
+        dst[out++] = (i + 1 < src_len) ? B64_ALPHABET[(v >> 6) & 0x3F] : '=';
+        dst[out++] = (i + 2 < src_len) ? B64_ALPHABET[v & 0x3F] : '=';
+    }
+    return out;
+}
+
+static inline size_t b64_decode(const char* src, size_t src_len, uint8_t* dst, size_t dst_cap) {
+    size_t out = 0;
+    int vals[4]; size_t vi = 0;
+    for (size_t i = 0; i < src_len && out < dst_cap; i++) {
+        if (src[i] == '=') break;
+        int v = b64_decode_char(src[i]);
+        if (v < 0) continue;
+        vals[vi++] = v;
+        if (vi == 4) {
+            dst[out++] = (uint8_t)((vals[0] << 2) | (vals[1] >> 4));
+            if (out < dst_cap) dst[out++] = (uint8_t)((vals[1] << 4) | (vals[2] >> 2));
+            if (out < dst_cap && i + 1 < src_len && src[i + 1] != '=')
+                dst[out++] = (uint8_t)((vals[2] << 6) | vals[3]);
+            vi = 0;
+        }
+    }
+    if (vi == 3 && out < dst_cap) {
+        dst[out++] = (uint8_t)((vals[0] << 2) | (vals[1] >> 4));
+        if (out < dst_cap) dst[out++] = (uint8_t)((vals[1] << 4) | (vals[2] >> 2));
+    } else if (vi == 2 && out < dst_cap) {
+        dst[out++] = (uint8_t)((vals[0] << 2) | (vals[1] >> 4));
+    }
+    return out;
+}
+
 /* ── Глобальное состояние (определено в chat_core.c) ── */
 
 struct chat_core_ctx {

src/chat/chat_msg.c

@@ -116,7 +116,10 @@ static void on_media_registered(void* arg, int err, const struct media_index_res
     if (!full_data) { DEBUG_ERROR(DEBUG_CATEGORY_DB_SYNC, "%s: data alloc fail", CC_ID); u_free(mctx); return; }
 
     size_t off = 0;
-    if (base_len > 0) { memcpy(full_data + off, mctx->msg_data, base_len); off += base_len; }
+    if (base_len > 0) {
+        char b64[2048]; size_t b64len = b64_encode(mctx->msg_data, base_len, b64, sizeof(b64));
+        memcpy(full_data + off, b64, b64len); off += b64len;
+    }
     off += snprintf(full_data + off, fdcap - off, "|%lld|%lld|%d|",
                     (long long)result->file_size, (long long)result->block_size, nb);
     for (int i = 0; i < 16; i++) off += snprintf(full_data + off, fdcap - off, "%02x", result->media_id[i]);
@@ -549,6 +552,9 @@ void on_msg_inserted(struct DB_SYNC_INSTANCE* si, uint64_t record_ts, const char
             while (body[bfi] && body[bfi] != '|' && bfi < sizeof(base_filename) - 1)
                 base_filename[bfi++] = body[bfi];
             base_filename[bfi] = '\0';
+            /* base64-decode display prefix (encoded in on_media_registered) */
+            uint8_t dec[256]; int dlen = (int)b64_decode(base_filename, bfi, dec, sizeof(dec));
+            if (dlen > 0 && dlen < (int)sizeof(base_filename)) { memcpy(base_filename, dec, (size_t)dlen); base_filename[dlen] = '\0'; }
             if (bfi == 0) snprintf(base_filename, sizeof(base_filename), "file");
 
             const uint8_t* sig_field = strstr(data, "\"sig\":\"");
@@ -630,6 +636,8 @@ void chat_core_attachment_download(const char* channel_id, int64_t msg_id) {
     while (body[bfi] && body[bfi] != '|' && bfi < sizeof(base_filename) - 1)
         base_filename[bfi++] = body[bfi];
     base_filename[bfi] = '\0';
+    uint8_t dec[256]; int dlen = (int)b64_decode(base_filename, bfi, dec, sizeof(dec));
+    if (dlen > 0 && dlen < (int)sizeof(base_filename)) { memcpy(base_filename, dec, (size_t)dlen); base_filename[dlen] = '\0'; }
     if (bfi == 0) snprintf(base_filename, sizeof(base_filename), "file");
 
     uint8_t author_sig[64]; memcpy(author_sig, sig_blob, 64);