Add the guard that confines each benchmark arm's agent to exactly one
tool, so a result measures the tool rather than the agent's choice
between tools.
`guardCommand` inspects every binary a proposed shell command would
reach — across pipelines, sequences, subshells, command and process
substitutions, redirections, and leading environment assignments — and
permits only the active arm's one allow-listed binary plus a curated set
of harmless read-only utilities. Foreign binaries, absolute-path
evasions (even of the arm's own binary), and interpreter-based fetch
tricks are denied; the gitea-mcp arm runs with the shell disabled
entirely. `provisionArmBin` produces a curated per-arm bin directory
exposing only that arm's binary as the convenience layer behind the
authoritative guard.
Tests are colocated in bench/guard.test.ts and run via `npm run
test:bench`.
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.
