Decodes a TRANSACTION_PAYLOAD_EVENT (type 40) body into the inner event stream of the transaction it wraps — the binlog_transaction_compression consumer arm (ADR-0011).

Body layout (MySQL server source, libbinlogevents/src/codecs/binary.cpp, read first-hand): a net_field_length TLV header — triples of (type, value_length, value) closed by a bare 0 end mark — followed by the payload bytes. Field types: 0 end mark, 1 payload size, 2 compression type, 3 uncompressed size; unrecognized fields are skipped by their length. The compression type value is 0 for ZSTD and 255 for NONE (compression/base.h) — only ZSTD is consumed; anything else fails closed.

The payload is one or more zstd frames (Capstan.Zstd). The inflated bytes are the transaction's events — QUERY(BEGIN), TABLE_MAP, row events, terminator — each a plain 19-byte header + body with no per-event CRC trailer (the outer type-40 event's CRC32 covers the compressed payload as a whole; observed live, the inner headers' event_size values sum exactly to the inflated length). Splitting is driven by each inner header's event_size.

Every divergence from the declared shape — a missing field, a size that does not fit, an unknown compression type, a zstd corruption signal, an uncompressed-size mismatch, a malformed inner header — is {:error, reason}, never a guess. All reasons are value-free (Rule 1): the payload and inner bytes carry row values and DDL text and never enter an error term.