Memory leak in connection pool handler

[stranske]

Bug Report

Describe the bug
Memory usage grows continuously over time, eventually causing OOM errors.

To Reproduce

1. Run the application for 24+ hours
2. Monitor memory usage
3. Observe steady growth even with no active connections

Expected behavior
Memory usage should stabilize after initial warmup.

Metrics

• Initial memory: 512MB
• After 24h: 4GB+
• After 48h: OOM kill

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Test Case: Fresh validation after PR #733 merge. Should get ONLY bug label.