[PM-38324] Optimize DeleteSendsJob

[harr1424]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-38324

📔 Objective

During resolution of bitwarden/clients#16965 DbOps suggested a few improvements to the DeleteSendsJob.

• Chunked fetch — add to Send_ReadByDeletionDateBefore and loop in the job so one run can't  pull an unbounded backlog into memory + a tight delete loop.

• Set-based Send_DeleteMany — delete the batch in one statement and bump each affected user once (collapsing  N bumps  ~distinct-user count), instead of N separate Send_DeleteById calls.

• Optionally throttle between batches so a backlog drain spreads out rather than saturating the Hyperscale log.

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

Reviewed the chunked DeleteSendsJob loop and its three stop conditions (empty batch, zero-progress/cumulative-skip guard, short batch), the new DeleteManySendsAsync batch command and its blob-failure skip semantics, and both ORM DeleteManyAsync implementations for delete/revision-bump atomicity and post-commit storage recompute. Verified the Send_DeleteMany and Send_ReadByDeletionDateBefore procedures against the dated migration and the SSDT sources, confirmed the @BatchSize default keeps the read procedure backward compatible during a rolling deploy, and confirmed IX_Send_DeletionDate supports the new TOP (@BatchSize) ... ORDER BY [DeletionDate] plan. Checked that every GetManyByDeletionDateAsync caller and both ISendRepository / INonAnonymousSendCommand implementations were updated, and read the new Admin, Core, and integration tests.

Findings from earlier review rounds were re-verified at ea0f7f8c7 and are resolved; no new findings this round.

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.40%. Comparing base (25f1f9c) to head (ea0f7f8).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...ucture.Dapper/Tools/Repositories/SendRepository.cs	82.60%	4 Missing ⚠️
...tityFramework/Tools/Repositories/SendRepository.cs	86.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8282      +/-   ##
==========================================
+ Coverage   63.66%   69.40%   +5.73%     
==========================================
  Files        2430     2467      +37     
  Lines      104962   105801     +839     
  Branches     9506     9560      +54     
==========================================
+ Hits        66822    73429    +6607     
+ Misses      35844    29936    -5908     
- Partials     2296     2436     +140     

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