Replace Vitest's hash-based --shard with a coordinator-side
longest-processing-time assignment. The coordinator collects the
instrumented inventory from a vitest list run (dropping the exempt
heavy suites that list does not exclude), reads per-file durations from
the Vitest results cache, and seeds heavy subprocess-bound suites into
different partitions. A weight-aware test fails when assignment ignores
recorded weights, verified by injecting a file-count-only rule.
Windows coverage measured partition spread of 442s (275-717s) under
hash sharding; a simulation with the same file durations and the new
assignment balances partitions to within 21s, cutting the critical
partition to roughly half.
10b31043ab