Merge branch 'kk/merge-base-exhaustion' into seen

The merge-base computation has been optimized by stopping the walk early when one side's exclusive commits in the queue are exhausted, yielding significant speedups for queries with one-sided histories. * kk/merge-base-exhaustion: commit-reach: remove commit-date ordering fallback commit-reach: move min_generation check into paint_queue_get() commit-reach: terminate merge-base walk when one paint side is exhausted commit-reach: introduce struct paint_state with per-side counters t6600: add clock-skew topologies and step counts for edge cases commit-reach: add trace2 instrumentation to paint_down_to_common() t6099, t6600: add side-exhaustion regression tests t6600: add test cases for side-exhaustion edge cases test-lib-functions: improve diagnostic output for trace2 data assertions Documentation/technical: add paint-down-to-common doc