hashindex: track unresolved pack location with F_PENDING flag

[mr-raj12]

Description

A chunk's pack location (pack_id, obj_offset, obj_size) isn't known yet between put() buffering it in the PackWriter and flush() writing the pack. The old code signalled this by writing the UNKNOWN_BYTES32 sentinel into pack_id and comparing against it later. Since every 256-bit value is a valid pack_id, reserving one as a marker is in-band signalling.

This replaces that with a ChunkIndex user flag, F_PENDING. add() sets it, update_pack_info() clears it once the real location is known, and is_pending() is the query used by repository.list() and get() in place of the old sentinel comparison. UNKNOWN_BYTES32 is still written as filler for the fixed-width record, but nothing reads it for meaning now.

Follow-up to #9821.

Checklist

• PR is against master
• New code has tests and docs where appropriate
• Tests pass (run tox or the relevant test subset)
• Commit messages are clean and reference related issues

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.14%. Comparing base (2dcb50f) to head (1206808).
⚠️ Report is 11 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/borg/repository.py	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9828      +/-   ##
==========================================
- Coverage   85.23%   85.14%   -0.09%     
==========================================
  Files          92       93       +1     
  Lines       15297    15337      +40     
  Branches     2299     2306       +7     
==========================================
+ Hits        13038    13059      +21     
- Misses       1570     1586      +16     
- Partials      689      692       +3     

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[ThomasWaldmann]

Not sure: maybe check whether it would be better to use a user flag for F_PENDING.

The slight complication you have in the hashindex code (can't use __setitem__) would go away and you could set/clear the flag from python code.

The "system flags" are rather hashtable-internal things, like tracking what's new and then only writing what's new.

[mr-raj12]

Not sure: maybe check whether it would be better to use a user flag for F_PENDING.

The slight complication you have in the hashindex code (can't use __setitem__) would go away and you could set/clear the flag from python code.

The "system flags" are rather hashtable-internal things, like tracking what's new and then only writing what's new.

switched F_PENDING to a user