fix(server): enforce browse continuation point limit at capacity (#4036)

[romanett]

Backports the browse continuation point limit fix from master (commit 1eb5e0c, PR #4036) to master378.

Problem

An off-by-one error in browse continuation-point retention allowed one extra browse continuation point to remain active. The eviction check only removed the oldest point when the count exceeded MaxBrowseContinuationPoints, so a session could hold MaxBrowseContinuationPoints + 1 points.

Fix

In Session.SaveContinuationPoint, evict the oldest point as soon as the session reaches the configured limit (>= instead of >), so at most MaxBrowseContinuationPoints points remain active.

Tests

Adds SessionContinuationPointsTests.SaveContinuationPointEvictsOldestWhenCountReachesConfiguredLimit, a regression test that saves one more than the configured limit and asserts the oldest point is evicted while exactly the configured number are retained. Verified it fails against the pre-fix code and passes with the fix.

Note: The upstream commit modified the refactored SessionContinuationPoints class, which does not exist on master378. The equivalent change here is applied to Session.SaveContinuationPoint, and the regression test is written against the master378 Session/ISession API.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.19%. Comparing base (db256c6) to head (bdc745b).

Additional details and impacted files

@@              Coverage Diff              @@
##           master378    #4270      +/-   ##
=============================================
- Coverage      60.19%   60.19%   -0.01%     
=============================================
  Files            378      378              
  Lines          79067    79067              
  Branches       13838    13838              
=============================================
- Hits           47598    47594       -4     
- Misses         27047    27049       +2     
- Partials        4422     4424       +2     

Files with missing lines	Coverage Δ
Libraries/Opc.Ua.Server/Session/Session.cs	60.47% <100.00%> (+0.19%)	⬆️

... and 9 files with indirect coverage changes

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