[scotthart]

This PR adds the spanner_internal::OperationContextFactory and integrates the previous PRs to complete the Request ID header functionality.

[gemini-code-assist]

Code Review

This pull request introduces a generalized OperationContext mechanism to inject request IDs and track attempt lifecycles across retries, generalizing the Bigtable generator option and implementing a robust request ID tracking system in the Spanner client. The review feedback highlights critical thread-safety and correctness issues: a broken double-checked locking pattern in DefaultSpannerOperationContextFactory::StaticPrefix() that introduces data races, a thread-safety hazard in ProcessRandomId() due to returning a reference to a mutable static string instead of returning by value, and a bug in BatchWriteGuard where premature stream cancellation incorrectly reports a successful status.

[codecov]

Codecov Report

❌ Patch coverage is 90.89286% with 51 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.34%. Comparing base (19d0185) to head (ef1dddb).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
google/cloud/spanner/internal/session_pool.cc	81.08%	21 Missing ⚠️
...nner/internal/spanner_operation_context_factory.cc	82.08%	12 Missing ⚠️
...internal/spanner_operation_context_factory_test.cc	87.20%	11 Missing ⚠️
google/cloud/spanner/internal/connection_impl.cc	96.29%	5 Missing ⚠️
...gle/cloud/spanner/internal/connection_impl_test.cc	97.61%	1 Missing ⚠️
google/cloud/spanner/internal/session_pool_test.cc	98.64%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16448      +/-   ##
==========================================
- Coverage   92.34%   92.34%   -0.01%     
==========================================
  Files        2254     2257       +3     
  Lines      215168   215559     +391     
==========================================
+ Hits       198699   199058     +359     
- Misses      16469    16501      +32     

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[scotthart]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces SpannerOperationContextFactory and its default implementation to manage the creation of OperationContext instances across various Spanner operations, enabling better tracking of request IDs, channel IDs, and attempt counts. It updates ConnectionImpl, SessionPool, and associated tests and benchmarks to utilize this factory, and adds channel ID tracking to maintain channel affinity. Feedback on the changes highlights a potential null pointer dereference in the DefaultSpannerOperationContextFactory constructor if process_random_id is null, suggesting a defensive fallback to ProcessRandomId().