Compared raw cdir bytes between original UC2 Pro and UC2 v3 archives
(using fixed bitdump.py match decoder). Key finding: the original
NEVER uses SuperMaster (masterPrefix=0) in file COMPRESS records —
it always assigns custom master indices (>= 2). UC2 v3 uses
SuperMaster for ungrouped files.
The original's ExtractFiles() processes SuperMaster files through
ToToWalk(TTefl, SUPERMASTER, ...) which hangs. Custom master files
go through the masroot chain walk, which works correctly.
Fix: always assign custom master indices to all files, generating at
least one custom master block even for archives without dedup groups.
This matches the original's behavior.
Other differences found: original uses hidden=0xDE (sentinel), tag=0
(no EXTMETA), method=3, and csize=8 (much smaller due to custom
master compression).
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