fix(cicd): stop benchmark.sh deleting the tracked scripts/benchmark harness

[ousamabenyounes]

Summary

• scripts/benchmark.sh deleted the tracked scripts/benchmark/ TypeScript VM-benchmark harness from the working tree on every local run.
• Wipe only the three gitignored output subdirectories (unix/, rtk/, diff/) instead of the whole $BENCH_DIR.

Follow-up to #3430 — @KuSh asked for this in the merge comment.

Problem

BENCH_DIR="$(pwd)/scripts/benchmark"

if [ -z "$CI" ]; then
  rm -rf "$BENCH_DIR"
  mkdir -p "$BENCH_DIR/unix" "$BENCH_DIR/rtk" "$BENCH_DIR/diff"
fi

.gitignore only ignores the three output subdirectories:

scripts/benchmark/diff/
scripts/benchmark/rtk/
scripts/benchmark/unix/

$BENCH_DIR itself is tracked and also holds the VM-benchmark harness — run.ts, cleanup.ts, rebuild.ts, lib/report.ts, lib/test.ts, lib/vm.ts, cloud-init.yaml. So rm -rf "$BENCH_DIR" removed all 7 of them.

The guard is [ -z "$CI" ], so CI never hits it (fresh checkout anyway) — it only fires locally, i.e. exactly when a contributor runs the benchmark before pushing.

Test verification (RED → GREEN)

There is no shell test harness in this repo, so this is a real observed run of the setup block against a clean checkout.

RED — on unmodified develop (ba7a9ce):

tracked files before: 7 / present on disk: 7
tracked files after:  7 / present on disk: 0
git status:
   D scripts/benchmark/cleanup.ts
   D scripts/benchmark/cloud-init.yaml
   D scripts/benchmark/lib/report.ts
   D scripts/benchmark/lib/test.ts
   D scripts/benchmark/lib/vm.ts
   D scripts/benchmark/rebuild.ts
   D scripts/benchmark/run.ts
output dirs created: scripts/benchmark/diff scripts/benchmark/rtk scripts/benchmark/unix

GREEN — with this patch:

tracked files before: 7 / present on disk: 7
tracked files after:  7 / present on disk: 7
git status:
output dirs created: scripts/benchmark/diff scripts/benchmark/rtk scripts/benchmark/unix

Stale output is still cleared — seeded a STALE.md in each of the three output dirs, ran the block again:

stale files left: 0
tracked harness intact: 7/7

Full local CI replay, CI deliberately unset so the local path is the one exercised:

job	develop (ba7a9ce)	this branch
test presence	PASS	PASS
fmt	PASS	PASS
clippy	PASS	PASS
test (--all)	PASS	PASS
build release	PASS	PASS
benchmark	34 good / 27 warn / 0 negative / 1 fail	34 good / 27 warn / 0 negative / 1 fail
tracked harness surviving the run	0/7	7/7

The benchmark's single remaining ❌ (empty output) is pre-existing and identical on develop.

Test plan

• cargo fmt --all && cargo clippy --all-targets -- -D warnings && cargo test --all
• ./scripts/benchmark.sh with CI unset — harness intact afterwards

[KuSh]

LGTM thanks