feat: add benchmark reporting command (task 0031)

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.

.claude/tasks/0031-bench-report-cli.md

@@ -0,0 +1,34 @@
+---
+spec: benchmark-harness
+blocked-by: [0030-bench-aggregator-and-reporting]
+---
+
+## What to build
+
+The maintainer-facing command that renders the accumulated sample store as the readable comparison, so the aggregator seam built in slice 0030 has a runnable entry point instead of being callable only from code.
+The command opens the store, drains it, aggregates against the scored suite and bonus definitions, and prints the report — `renderReport(aggregate({ records: readAllSamples(store), suite, bonus }))` — to stdout.
+
+It renders whatever has accumulated so far, annotating incomplete coverage rather than blocking on a complete matrix, exactly as the aggregator already does; the command adds only the argument seam and the live store/stdout boundary.
+It is the reporting counterpart to `bench:run` (slice 0029): `bench/report.ts` stands over `bench/aggregate.ts` in the same shape as `bench/run.ts` stands over `bench/run-loop.ts`.
+
+## Acceptance criteria
+
+- [x] A `bench:report` command reads the accumulated store and prints the rendered report to stdout.
+- [x] The store root defaults to `DEFAULT_STORE_ROOT` (`bench/results`) and is overridable with `--store`, matching `bench:run`.
+- [x] The report is produced solely by driving the `readAllSamples` / `aggregate` / `renderReport` seam and the scored suite / bonus definitions from earlier slices — no aggregation, weighting, or rendering is reimplemented in the command.
+- [x] A partial or empty store renders without error (incomplete coverage annotated, an unrun arm shown as an em dash), inheriting the aggregator's behaviour rather than special-casing it.
+- [x] The argument parser is a pure, unit-tested seam (`--store`, `--help`, plus the `--self-review` / `--no-self-review` variant selector — see Implementation Notes), matching the `parseRunArgs` convention. Because the report boundary is offline, the whole command — not just the parser — is deterministic and unit-tested, rather than validated only by running it.
+
+## Implementation Notes
+
+- **Shape mirrors `bench/run.ts`.** `parseReportArgs` is the pure argument seam; `runReportCommand(argv, deps, out)` opens `createSampleStore(storeRoot)`, drives `renderReport(aggregate({ records: readAllSamples(store), suite, bonus }))`, and prints line-by-line through `out`; `main` and the `import.meta`/`argv[1]` direct-execution guard match `run.ts`. Added the `bench:report` script (`tsx bench/report.ts`) and replaced the flagged follow-up note in `bench/README.md` (plus a new "Reading the results" section).
+
+- **The boundary is offline, so the whole command is unit-tested (deviation from the criterion's framing).** Criterion 5 as written assumed the run-command pattern where the live boundary is "validated by running it." But the report reads only the local sample store — no credentials, host, or Agent SDK — so `runReportCommand` is deterministic and is covered by real unit tests over a temp-dir store (populated, empty, and `--help`), not just the parser. It was still verified by running `npm run bench:report` end-to-end. The unused `deps` parameter is retained only for signature parity with the command family (commented at the parameter).
+
+- **Added `--self-review` / `--no-self-review` — beyond the written `(--store, --help)` seam, deliberately.** `aggregate` needs a `suite` and `bonus`, and `buildScoredSuite`/`buildBonusTasks` are parameterized by `selfReviewPermitted`: when self-review is unavailable the two review tasks render as comment reviews in the scored suite and the approve/request-changes pair moves into the bonus catalog. `bench:run` resolves this by probing the live host (`detectSelfReviewSupport`); the offline report has no host to probe, so it cannot detect it and would otherwise have to hardcode one variant silently. The flag makes the choice explicit, defaulting to `true` (matching the richer self-review-permitted configuration). It is well-scoped: the scored coverage is identical either way, so it only selects the bonus capability catalog — documented in `--help` and the README. Criterion 5's "`--store`, `--help`" wording was updated to record it.
+
+- **`DEFAULT_STORE_ROOT` moved to `store.ts`.** It was defined in `run.ts`; its natural home is the store, and both commands now need it, so it lives in `store.ts` as the single source of truth and is re-exported from `run.ts` to keep that command's existing importers (and `run.test.ts`) resolving it unchanged.
+
+- **Tests, TDD.** `bench/report.test.ts` (8 tests) was authored test-first by the test-writer sub-agent from the public interface alone: the parser defaults/overrides/rejection/help, and the command over populated/empty/help paths. As with the `run-loop` slice, the parser is a small cohesive unit whose logic all landed in one GREEN, so the parser cases past the first are passing characterization guards rather than red-first cycles; the `runReportCommand` cell had a genuine red first. Full bench tier green (104 tests), typecheck clean.
+
+- **Review (three-axis, `/review-uncommitted`): Risk overall Low.** Spec axis: all five criteria met; the only finding was that `--self-review` exceeded the written seam — justified in substance, now recorded here and in the criterion. Standards axis: no hard violations; two judgement calls — the `parseReportArgs` flag loop partly overlaps `parseRunArgs` but has genuinely diverged (adds `--no-` negation), left unextracted as the reviewer advised (a shared parser would be premature); and the unused `deps` parameter, addressed with a parity comment.