A real download came back as BigBuf memory (0xDEADBEEF poison) with a PM3 response
magic (0x62334d50) embedded — the classic signature of a desynced read: the stream
had stale bytes (a prior partial transaction, or the C client having touched the
port), and the bulk reader consumes fixed 544-byte OLD frames that carry no magic to
resync on, so once misaligned it stays misaligned and reads memory as "samples".
transport.download_bulk now flushes the input first (reset_input_buffer + drain the
asyncio StreamReader until an 80ms quiet gap), so the transfer always begins byte-
aligned. Drains no-op when disconnected. Test asserts the flush runs before the request.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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