Counterbalanced diagnostic: replay auditor and 420 fast tests

Adds the independent auditor for #84's frozen six-order comparison. It checks all planned rows, policy/execution/feedback replay, fresh state between orders, diagnostic purity, RNG offsets, and CPU/gate summaries. Raw-attempt replay streams without retaining every graph in memory.

Validation: 46 affected tests passed; all 420 fast tests passed in 234.598 s, with unchanged source hashes and no skips or exclusions. Commands ran serially under the builder lock. Slow/retry and local full discovery were not run for this additive diagnostic path. The initial synthetic-test failure and its correction are retained.

The comparison has not been measured yet. Original runtime, frozen corpora and negative results remain unchanged. #84 remains open.