recreate: also do the work if --timestamp is the only change requested

[ThomasWaldmann]

Problem

borg recreate -a ARCHIVE --timestamp ... with no other change requested (no PATHs/patterns, no --chunker-params, no --comment) printed Skipped archive ...: Nothing to do. and silently did not apply the requested timestamp, contradicting the option's help text.

The work-trigger gate in ArchiveRecreater.recreate() only considered the matcher, rechunking and the comment — not self.timestamp, although the value is correctly plumbed all the way to target.save(timestamp=...).

Fix

Include self.timestamp is None in the gate.

Tests

test_recreate_with_given_timestamp now passes only --timestamp (previously it also passed --comment, which triggered the work and masked this bug) — it fails on master and passes with this fix.

Both timestamp tests also gave the archive name as a positional argument, but recreate positionals are PATHs in borg2: this made the matcher accidentally non-empty (also masking the bug) and recreated the archive with zero items, unnoticed. They now select the archive via -a and assert that the items survive the recreate.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.69%. Comparing base (0adbb7a) to head (46030f3).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10302      +/-   ##
==========================================
+ Coverage   87.65%   87.69%   +0.03%     
==========================================
  Files         103      103              
  Lines       18702    18712      +10     
  Branches     2877     2880       +3     
==========================================
+ Hits        16393    16409      +16     
+ Misses       1609     1600       -9     
- Partials      700      703       +3     

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