fix: flush migration logs after each process message

[Nikolas Evers (vintagesucks)]

failing nightly 2026-10-07 and #229's merge, with a green nightly in between, all on the same commit

• LoggingService writes its buffer every 50 entries¹, on a service reset, or when the PHP process ends. The admin worker's consume request never resets services² and keeps polling for up to 20 s³, so a run can finish with its last log entries still in memory (35 and 30 in the two failing runs)
• MigrationProcessHandler now flushes after each process message, so every batch's logs are stored before the next one runs

Footnotes

1. https://github.com/shopware/SwagMigrationAssistant/blob/d9ee89e697c03da9d5cc1989384860d36fb12d3f/src/Migration/Logging/LoggingService.php#L102-L103 ↩

2. https://github.com/shopware/shopware/blob/04ab398d47d25932684a6997db66ce72becb8e7d/src/Core/Framework/MessageQueue/Api/ConsumeMessagesController.php#L67-L81 ↩

3. 20 s time limit per request: https://github.com/shopware/shopware/blob/04ab398d47d25932684a6997db66ce72becb8e7d/src/Core/Framework/MessageQueue/Api/ConsumeMessagesController.php#L69 (default from https://github.com/shopware/shopware/blob/04ab398d47d25932684a6997db66ce72becb8e7d/src/Core/Framework/Resources/config/packages/shopware.yaml#L420), and it only returns early when no message was handled: https://github.com/shopware/shopware/blob/04ab398d47d25932684a6997db66ce72becb8e7d/src/Core/Framework/MessageQueue/Subscriber/EarlyReturnMessagesListener.php#L36-L40 ↩

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 65.36%. Comparing base (d191cfc) to head (7601855).
⚠️ Report is 1 commits behind head on trunk.

Files with missing lines	Patch %	Lines
src/DependencyInjection/migration.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #231      +/-   ##
============================================
- Coverage     65.36%   65.36%   -0.01%     
  Complexity     4786     4786              
============================================
  Files           654      654              
  Lines         21756    21758       +2     
============================================
+ Hits          14221    14222       +1     
- Misses         7535     7536       +1     

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