trace analysis

Thirty-two addresses per warp instruction, thousands of instructions: say what the pattern is and how many sectors it cost. The address-delta test for contiguous and strided, the sector count that measures the damage, the code that does both, and the edge cases (misalignment, inactive lanes, mixed widths).

Each rank keeps a ring buffer of its recent collectives, and on a timeout every rank dumps it. Comparing sequence numbers across a thousand of those buffers finds the missing participant in one pass, and the three patterns those comparisons produce point at three different causes.