Add the maintainer-facing `bench:report` command, the offline counterpart
to `bench:run`: it opens the sample store, drains it, aggregates against the
scored suite and bonus definitions, and prints the aggregator's comparison to
stdout. It renders whatever has accumulated, annotating incomplete coverage
rather than blocking on a complete matrix.
`parseReportArgs` is the pure argument seam (`--store`, `--help`, plus a
`--self-review` / `--no-self-review` variant selector). Unlike `bench:run` the
boundary is offline — it reads only the local store, no host or Agent SDK — so
the whole `runReportCommand` is deterministic and unit-tested, not smoke-run.
Move `DEFAULT_STORE_ROOT` to `store.ts` as the single source of truth,
re-exported from `run.ts` for its existing importers.
Lay the foundation the benchmark harness reads and writes: a bench/
directory (excluded from the published npm package), the immutable
result-record shape, and an append-only per-cell sample store.
- bench/result.ts: the ResultRecord shape — four token components,
turns, duration, imputed cost, tagged pass/fail outcome, and the
arm/task/tier/trial/timestamp tags. Arm and Tier are typed unions.
- bench/store.ts: append-only sample store, one JSONL file per cell at
<root>/<arm>/<taskId>.jsonl; deepening a cell only ever adds samples.
- bench/README.md: harness working docs and benchmark vocabulary, kept
out of the tool's domain glossary per the spec.
- Dedicated bench test tier (vitest.bench.config.ts, npm run test:bench)
kept out of the fast tier; tsconfig typechecks bench.
- Packaging tier asserts bench/ never ships in the tarball.
