feat(bb): centralize Chonk pinning around one canonical tarball + auto-regen on VK-UPDATE

[AztecBot]

Summary

Centralizes every Chonk benchmark and the VK consistency test around a single
pinned IVC-inputs tarball, decouples them from the slow e2e regen path, and
revives an auto-regenerate-on-VK-UPDATE: mechanism that pushes the new pin
back to the PR with [skip ci].

Today there are two parallel artifacts: bb-chonk-inputs-<hash>.tar.gz (S3,
hand-pinned, used only by the VK-consistency test) and
bb-chonk-captures-<hash>.tar.gz (CI cache, regenerated by build_bench
running the e2e client flows, consumed by every chonk benchmark). The
benchmarks therefore pay the full TS + e2e cost on every cache miss, and a VK
update is a manual --update_inputs + commit dance.

After this PR:

• One canonical tarball, one pin file (barretenberg/cpp/scripts/chonk-inputs.hash).
• yarn-project/end-to-end/bootstrap.sh build_bench default = download +
  extract pinned tarball. Set BUILD_BENCH_REGEN=1 to regenerate from
  scratch (used only by regenerate_chonk_inputs.sh).
• VK-consistency test (test_chonk_standalone_vks_havent_changed.sh),
  in-browser memory bench, and ci_benchmark_ivc_flows.sh all consume
  example-app-ivc-inputs-out populated by the same pinned download via
  the shared chonk_inputs_lib.sh library.
• ci-fast / ci-full now call scripts/ci_vk_update.sh on test failure;
  if the PR contains a VK-UPDATE: <reason> empty commit, CI runs
  regenerate_chonk_inputs.sh --push which builds bb (AVM=ON), regenerates
  inputs, proves+verifies each flow, uploads the new tarball, rewrites
  chonk-inputs.hash, rebases the pin commit onto the latest PR head, and
  pushes back with [skip ci] in the commit subject so CI does not loop.
• Push handles concurrent commits via fetch → rebase → push with retry.
  The pin commit only ever touches one one-line file, so race conditions
  resolve cleanly.

Files

• barretenberg/cpp/scripts/chonk-inputs.hash (new) — single source of truth.
• barretenberg/cpp/scripts/chonk_inputs_lib.sh (new) — sourced helpers:
  chonk_inputs_hash, chonk_inputs_url, chonk_inputs_s3_uri,
  chonk_inputs_download, chonk_inputs_upload, chonk_inputs_set_pin.
• barretenberg/cpp/scripts/regenerate_chonk_inputs.sh (new) — orchestrator
  with --no-commit | --commit | --push + --reason.
• scripts/ci_vk_update.sh (new) — CI hook that detects VK-UPDATE: and
  invokes the orchestrator with --push.
• barretenberg/cpp/scripts/test_chonk_standalone_vks_havent_changed.sh —
  pin lookup now goes through the library; --update_inputs delegates to
  the orchestrator; failure message tells authors how to acknowledge.
• yarn-project/end-to-end/bootstrap.sh — build_bench default is a tiny
  pinned-download; BUILD_BENCH_REGEN=1 keeps the slow e2e regen path.
• bootstrap.sh — ci-fast / ci-full invoke ci_vk_update.sh on test
  failure.
• barretenberg/cpp/CLAUDE.md — documents the VK-UPDATE: workflow + new
  fast-path bootstrap behavior.

Design notes

• The pin file is deliberately a separate one-line file rather than an inline
  variable in test_chonk_standalone_vks_havent_changed.sh. Hash bumps then
  produce a one-line diff and never perturb the script's own
  .rebuild_patterns hash (avoids the kind of rebuild race that chore: shrink msm test size while maintaining coverage #23226
  patched around).
• The VK-UPDATE: convention is the user-facing trigger. There is no
  dedicated workflow file — the existing ci3.yml lane already gives us
  the right hook point.
• [skip ci] is enforced in the commit subject so the auto-push cannot
  loop. CI on the next manual push picks up the new pin and the VK check
  passes.
• chonk_inputs_download is idempotent and short-circuits when the
  destination already contains flow folders, so the bench engine can call
  it from many flows in parallel without re-downloading.

Follow-ups (out of scope)

• Move Chonk flow benchmark emission out of yarn-project/end-to-end and
  into barretenberg/cpp/bootstrap.sh bench_cmds, with the input prep
  declared as a barretenberg-level Make dep. That would let chonk benches
  schedule in parallel with TS tests instead of waiting on the bench phase.
• A /repin-chonk-inputs PR-comment trigger if the VK-UPDATE: empty-commit
  convention proves too awkward.

Test plan

• bash -n on every touched / new script.
• Functional sanity of chonk_inputs_lib.sh (hash/url/s3 helpers print the
  expected strings from the new pin file).
• The standalone VK test, when run with the unchanged pinned hash, falls
  through to parallel … check_circuit_vks exactly as before; the only
  visible difference is the pin source.
• CI on this PR exercises ci_vk_update.sh (no VK-UPDATE: commit → no-op).
• A follow-up PR will land a VK-UPDATE: empty commit on an intentional VK
  change to validate the end-to-end auto-push path against current CI.

---

Created by claudebox · group: slackbot

[AztecBot]

Automatically closing this stale claudebox draft PR (no updates for 5+ days). Re-open if still needed.