Session Manager Concurrency Fix

[gregory-at-cvs]

PR #1: Session Manager Concurrency Fix

Description

The changes fix a thread-safety issue in SessionManager where concurrent calls to getSessionId()
could create duplicate sessions during session timeout/expiration.

Problem

The existing code had a documented TODO acknowledging this race condition:

// TODO FIXME: This is not threadsafe -- if two threads call getSessionId()
// at the same time while timed out, two new sessions are created

Solution:

1. Changed session from mutable variable to AtomicReference
2. Implemented compare-and-set for atomic session updates
3. Only one thread successfully creates new session; others use the newly created one
4. Extracted observer notification into separate method for clarity
5. Added concurrency tests

Related PRs

This is part 1 of 3 in a session management enhancement:

This PR: Thread-safety fix (foundation)
PR 2: Session infrastructure (depends on this)
PR 3: Session telemetry integration (depends on PR 2)
Review order: This PR should be reviewed and merged first.

Type of Change

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature
[ ] Breaking change
[x] Documentation update

Checklist

[x] Code follows project style guidelines (spotless applied)
[x] Self-review completed
[x] Added tests that prove the fix is effective
[x] New and existing tests pass locally
[x] Documentation updated where applicable

Additional Context

This uses the atomic compare-and-set pattern commonly used for thread-safe operations in Java/Kotlin.

Part of a larger effort: We're contributing session management enhancements to bring Android SDK to parity with iOS (spans/logs) and beyond (metrics). This PR is the foundation - fixing a known thread-safety issue before building on it.

Related information: https://opentelemetry.io/docs/specs/semconv/general/session/

Related PRs

This is part 1 of 3 in a comprehensive session management enhancement:

• This PR: Thread-safety fix (foundation)
• PR 2: Session infrastructure (depends on this)
• PR 3: Session telemetry integration (depends on PR 2)

Review order: This PR should be reviewed and merged first, as PRs 2 and 3

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: gregory-at-cvs / name: Gregory Rasmussen (88fe715, da961df)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.59%. Comparing base (7e5a63e) to head (da961df).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1419      +/-   ##
==========================================
- Coverage   63.65%   63.59%   -0.07%     
==========================================
  Files         159      159              
  Lines        3134     3137       +3     
  Branches      326      326              
==========================================
  Hits         1995     1995              
- Misses       1042     1044       +2     
- Partials       97       98       +1     

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