PSSI tag parser will fail on version=1 song structure data

[devicelocksmith]

Bug

The PSSI (Song Structure) tag parser in anlz/structs.py uses Const(24, Int32ub) as the first field of the tag content:

AnlzTagSongStructure = Struct(
    "len_entry_bytes" / Const(24, Int32ub),
    "len_entries" / Int16ub,
    ...
)

This interprets bytes 0-3 of the tag content as a single 32-bit constant 0x00000018. However, the actual binary layout is two separate 16-bit fields:

Offset	Size	Field
0-1	Int16ub	version (0 or 1)
2-3	Int16ub	entry_size (24 = 0x0018)
4-5	Int16ub	entry_count
6-7	Int16ub	mood

For version=0, bytes 0-3 are 00 00 00 18, which happens to match Const(24, Int32ub). But for version=1, bytes 0-3 would be 00 01 00 18 = 0x00010018, causing a ConstError.

Hardware devices that parse ANLZ files validate version > 1 and reject with an "unsupported version" error, confirming that both version 0 and version 1 are valid tag versions.

Suggested Fix

AnlzTagSongStructure = Struct(
    "version" / Int16ub,                    # 0 or 1
    "len_entry_bytes" / Const(24, Int16ub), # always 0x0018
    "len_entries" / Int16ub,
    ...
)

The XOR deobfuscation mask start index also depends on the version field: mask_start = version % 19.

Additional context

The XOR deobfuscation mask is derived from the ASCII string "Kanzen-niRikaishita" (19 bytes). Each byte of the base mask is seed_char + 0x80, and entry_count is added per-byte at runtime. This matches your existing static mask + entry_count formulation — just a different (equivalent) way to express the same computation. Documenting the seed string may be useful for understanding future format changes.