From 93bb8e7c6e6346db0da5eca87732e7fe9257995d Mon Sep 17 00:00:00 2001
From: zzstoatzz <thrast36@gmail.com>
Date: Wed, 12 Aug 2026 13:25:07 -0500
Subject: [PATCH] wire: sync blocks are the atproto $bytes sentinel, not a bare
 base64 string
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the d4dd2f0 differential oracle's live cutover rejected our #sync
frames: a lexicon bytes value is {"$bytes":"<unpadded std base64>"}
per the data-model spec (atmos cbor.AppendJSONBytes documents that a
bare string is rejected by conformant decoders — and it was). all
seven upstream oracle tests pass locally against the pin.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 src/internal/serve/wire.zig | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/src/internal/serve/wire.zig b/src/internal/serve/wire.zig
index 46841fd..599d1f9 100644
--- a/src/internal/serve/wire.zig
+++ b/src/internal/serve/wire.zig
@@ -513,8 +513,18 @@ pub fn encodeSyncV2(w: *std.Io.Writer, args: struct {
     try s.write(seq);
     try s.objectField("sync");
     try s.beginObject();
+    // lexicon "bytes" value: the {"$bytes":"<unpadded std base64>"} sentinel
+    // (atmos cbor.AppendJSONBytes) — a bare base64 string is rejected by
+    // conformant decoders (caught live by the d4dd2f0 differential oracle)
     try s.objectField("blocks");
-    try writeBase64String(&s, args.blocks);
+    try s.beginObject();
+    try s.objectField("$bytes");
+    try s.beginWriteRaw();
+    try s.writer.writeByte('"');
+    try writeBase64NoPad(s.writer, args.blocks);
+    try s.writer.writeByte('"');
+    s.endWriteRaw();
+    try s.endObject();
     try s.objectField("did");
     try writeString(&s, args.did);
     try s.objectField("rev");
@@ -534,22 +544,6 @@ pub fn encodeSyncV2(w: *std.Io.Writer, args: struct {
     try w.writeByte('}');
 }
 
-/// base64 std WITH padding, matching Go's []byte JSON encoding
-fn writeBase64String(s: *std.json.Stringify, data: []const u8) !void {
-    try s.beginWriteRaw();
-    try s.writer.writeByte('"');
-    const encoder = std.base64.standard.Encoder;
-    var chunk: [4]u8 = undefined;
-    var i: usize = 0;
-    while (i < data.len) : (i += 3) {
-        const n = @min(3, data.len - i);
-        const out = encoder.encode(&chunk, data[i..][0..n]);
-        try s.writer.writeAll(out);
-    }
-    try s.writer.writeByte('"');
-    s.endWriteRaw();
-}
-
 /// #info advisory (seq-less): {"$type":"message","payload":{"$type":"...#info","message"?,"name"}}
 pub fn encodeInfoV2(w: *std.Io.Writer, name: []const u8, message: ?[]const u8) !void {
     try w.writeAll(message_frame_prefix);
-- 
2.51.2