fix(tips): pad tip code payload with incrementing digits instead of zeros

services/opencode/src/androidTest/kotlin/com/getcode/opencode/model/core/OpenCodePayloadTests.kt

@@ -60,7 +60,8 @@ class OpenCodePayloadTests {
 
         assertEquals(PayloadKind.Tip.value, encoded[0].toInt())
         assertEquals(userId, encoded.subList(1, 17))
-        // Trailing bytes reserved / zero.
-        assertEquals(listOf<Byte>(0, 0, 0), encoded.subList(17, 20))
+        // Trailing reserved bytes are filled with incrementing digits (1, 2, 3) rather than
+        // zeros, so the native scanner can't drop them as trailing padding.
+        assertEquals(listOf<Byte>(1, 2, 3), encoded.subList(17, 20))
     }
 }

services/opencode/src/main/kotlin/com/getcode/opencode/model/core/OpenCodePayload.kt

@@ -85,10 +85,12 @@ data class OpenCodePayload(
 
    0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
- | T |                     User ID (16 bytes)                     |  reserved (0) |
+ | T |                     User ID (16 bytes)                     | 1 | 2 | 3 |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
 
  (T) Type (1 byte) — PayloadKind.Tip (2).
  User ID (16 bytes) — the recipient's user id (a UUID) so others can tip them. Raw bytes,
    no rendezvous keypair. Matches the iOS TipCode.Payload frame.
+ Reserved (3 bytes) — filled with incrementing digits (1, 2, 3) instead of zeros so the
+   native scanner doesn't strip them as trailing zero padding.
 */

services/opencode/src/main/kotlin/com/getcode/opencode/model/core/PayloadKind.kt

@@ -70,8 +70,9 @@ sealed interface PayloadKind {
 
     /**
      * A profile "tip code": the recipient's [UserId] (a 16-byte UUID) written raw at offset 1,
-     * with the trailing bytes reserved. Carries no nonce and derives no rendezvous — matches the
-     * iOS `TipCode.Payload` frame.
+     * with the trailing reserved bytes filled with incrementing digits (1, 2, 3, ...) so the
+     * native scanner can't drop them as trailing zero padding. Carries no nonce and derives no
+     * rendezvous — matches the iOS `TipCode.Payload` frame.
      */
     data object Tip : PayloadKind {
         override val value: Int = 2
@@ -84,6 +85,14 @@ sealed interface PayloadKind {
             userId.take(OpenCodePayload.USER_ID_LENGTH).forEachIndexed { index, byte ->
                 data[index + OpenCodePayload.OFFSET_USER_ID] = byte
             }
+
+            // Fill the reserved trailing space with incrementing digits (1, 2, 3, ...) rather
+            // than zeros, so `Scanner.decode` can't drop them as trailing zero padding and the
+            // frame round-trips at full length.
+            val reservedStart = OpenCodePayload.OFFSET_USER_ID + OpenCodePayload.USER_ID_LENGTH
+            for (index in reservedStart until OpenCodePayload.LENGTH) {
+                data[index] = (index - reservedStart + 1).toByte()
+            }
             return data
         }