AOT: crypto.createHash('sha256').update(buf).digest() returns Buffer with undefined length for FIRST call inside socket-callback context #88

Environment

• perry 0.5.97
• macOS arm64 (darwin 25.4.0)

Problem

Inside the socket 'data' callback path of a real MySQL connection, the first crypto.createHash('sha256').update(buf).digest() call returns a Buffer whose .length reads as undefined. Subsequent calls to the same function return correct 32-byte buffers.

At top level (no async context) or inside a plain setTimeout callback, all calls return correct 32-byte buffers. So this isn't a pure parity bug — it's context-sensitive.

Trace from inside @perry/mysql's sha256Scramble during caching_sha2_password auth:

  [sha256] input.len=7  digest.len=undefined    ← FIRST call, buggy
[scramble] sha256Pw.len=0                        ← .length reads as 0 in the caller
  [sha256] input.len=0  digest.len=32            ← SECOND call, fine
[scramble] sha256Sha256Pw.len=32
  [sha256] input.len=52 digest.len=32            ← THIRD call, fine
[scramble] inner.len=32
out.len=0 loop-bound=0                           ← loop never runs (bound=0)
sha256Scramble returned len=0                    ← driver sends empty auth_response

The first non-empty-buffer hash returns a digest whose .length is undefined at the callsite, which is silently coerced to 0 in the outer scramble routine. The subsequent hashes (including hashing the broken zero-length digest) work fine.

Discovered workaround

Priming the sha256 machinery with a throwaway empty call before the real first one restores correctness:

sha256(Buffer.alloc(0));        // throwaway — its digest.len is still 'undefined'
const real = sha256(pwBuf);      // now returns a 32-byte Buffer correctly

Hit in real code

@perry/mysql's caching_sha2_password auth path. Source layout:

src/auth/caching-sha2.ts:
  function sha256(b: Buffer): Buffer {
      const h = crypto.createHash('sha256');
      h.update(b);
      return h.digest();  // ← returns Buffer w/ undef length on first call in async ctx
  }
  export function sha256Scramble(password: string, challenge: Buffer): Buffer {
      const sha256Pw = sha256(Buffer.from(password, 'utf8'));  // ← len=0 here
      ...
  }

Before applying the prime workaround the driver sent a zero-byte auth_response in HandshakeResponse41 and the server rejected with errno 1045 ("Access denied ... using password: NO"). After priming, the driver authenticates cleanly.

The priming workaround feels like papering over a real codegen/runtime issue. Would be great to fix properly.

Separation from #86

#86 (closed / fixed in 0.5.95) covered the top-level case where digest returned typeof === 'number'. That part is fixed — typeof digest === 'object' now at top level AND in setTimeout. This new issue is specifically about:

1. The first call inside a socket 'data' event handler
2. The .length is undefined (not a number-return, the digest IS a Buffer-like object but its length metadata is missing)

Expected

digest.length is 32 on every call, regardless of async context.