[Suhas Aggarwal (suhasagg)]

Summary

Fix Purview in-memory cache byte accounting when replacing an existing
entry, particularly when the replacement requires eviction.

Problem

When an existing cache entry is replaced, its size is subtracted from
_current_size_bytes, but the old entry remains in _cache while
eviction runs.

If eviction encounters that entry, its size can be subtracted again,
causing _current_size_bytes to diverge from the actual size of the
live cache entries.

A regression test reproduced this on the existing implementation:

• tracked cache size: 154 bytes
• actual live-entry size: 206 bytes

Changes

• Remove an existing entry from _cache before adjusting its size.
• Run eviction against the actual set of live cache entries.
• Preserve stale expiry-heap handling.
• Add regression coverage for growing an existing entry when the cache
  is at capacity.
• Verify that tracked cache size matches the total size of live entries.

Testing

• Regression test before fix: failed as expected (154 != 206)
• Regression test after fix: passed
• Purview cache tests: 18 passed
• Purview non-integration tests: 200 passed
• Ruff check: passed
• Ruff format check: passed
• git diff --check: passed

Fixes #8988

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused fix resolves the double-subtraction bug and includes effective regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes Purview cache byte accounting when replacing entries during eviction.

Changes:

• Removes replaced entries before eviction.
• Adds regression coverage validating tracked size against live entries.

File	Description
python/​packages/​purview/​agent_framework_purview/​_cache.py	Corrects replacement accounting and eviction behavior.
python/​packages/​purview/​tests/​purview/​test_cache.py	Tests larger replacements at cache capacity.

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[Eduard van Valkenburg (eavanvalkenburg)]

Suhas Aggarwal (@suhasagg) Thanks for the contribution. This implements the same change as #8990, so we'll continue the work there and close this duplicate.