Server move fails: unpacker mishandles tar entries >100 chars ("Archive entry … is not listed in the manifest")

[amitav13]

What happened

Moving the server (serverMove experiment) to a second persistent Mac fails at Start the new server:

The machine couldn't unpack the export: Archive entry
attachments/proj_<id>/files/attachments/proj_<id>/<long-attachment-name>.svg
is not listed in the manifest

Earlier steps succeed: stop running work → update skipped (target already on 0.44.0) → export (192 MB) → send data to target. The server stays put, as documented.

Why (from inspecting the export)

The export archive itself looks correct. I ran bb server export and inspected it:

• The tar entry is files/attachments/proj_<id>/<name>.svg. The path is 146 characters, so it's written with a pax extended header (path= record). Python's tarfile and bsdtar read it correctly.
• manifest.json lists it as attachments/proj_<id>/<name>.svg, which matches once the files/ prefix is removed.
• It is the first entry in the archive longer than 100 characters. Every entry before it is shorter and unpacked fine.
• The unpacker on the target reports the name as attachments/proj_<id>/files/attachments/proj_<id>/<name>.svg. It looks like the pax path (or a ustar prefix/name split) is being joined onto the wrong base instead of replacing the header's name field.

This isn't specific to one file: 68,786 of the 68,920 entries in my export are longer than 100 characters, mostly files/plugins/cache/git/.... So any real-world server move will probably fail the same way.

Repro

1. Have a server with any stored file whose export path is longer than 100 characters (for example an attachment with a long generated filename, or any git plugin in plugins/cache).
2. bb settings experiment serverMove true
3. bb server move --to <other machine>; --check passes.
4. The move fails at "Start the new server" with the error above.

Environment

• bb-app 0.44.0 on both machines (macOS, Apple Silicon). The source server runs in the desktop app; the target is a manually enrolled persistent machine.
• bb connect address (not a direct URL).

Expected

The unpacker honours pax path records (and ustar prefix) for long names, so the move completes.

I haven't tried bb server import on the target yet, so I don't know whether the offline import shares the same unpacker.