Process completed with exit code 22.\\n```\\n\\nRelevant script: `actions/setup/sh/install_antigravity_cli.sh` lines 77-79 (the new `curl -fsSL --retry 3 ... ${CHECKSUMS_URL}` call).\\n\\n\\n\\n### Why this is a regression on main, not a PR-side defect\\n\\nPR-side change (#35694) does **not** touch the install script. Both runs below use the same `ENGINE_VERSION: 1.0.2-6113393518706688`, only the actions/script changed:\\n\\n| Run | Time (UTC) | Branch | Result | First action |\\n|---|---|---|---|---|\\n| [§26609936898](https://github.com/github/gh-aw/actions/runs/26609936898) | 2026-05-29 00:13 | `copilot/api-proxy-reflect-call-resilience` | success | `Downloading from (storage.googleapis.com/redacted) (no checksum download) |\\n| [§26639071214](https://github.com/github/gh-aw/actions/runs/26639071214) | 2026-05-29 13:11 | `copilot/expose-custom-api-auth-header-options` (PR #35694) | failure | `Downloading checksums from .../checksums.txt...` → 404 |\\n\\nBetween those two runs (≈ 13 hours) the install script was modified on `main` to add a SHA256 checksum download/verification step. The current `actions/setup/sh/install_antigravity_cli.sh` at HEAD performs `curl \\\\$\\\\{CHECKSUMS_URL}` before downloading the tarball — but the GCS bucket layout for `1.0.2-6113393518706688` does not include `checksums.txt`. So *any* Smoke Antigravity run on `main` (or any PR merging with `main`) will now fail at this step until the bucket is corrected or the script is updated.\\n\\n### Affected workflows / runs\\n\\n- Workflow: `Smoke Antigravity` (`.github/workflows/smoke-antigravity.lock.yml`)\\n- Failing run: [§26639071214](https://github.com/github/gh-aw/actions/runs/26639071214) — only 1 occurrence in the last 6h, but Smoke Antigravity runs on each PR — every subsequent PR run will hit this until fixed.\\n\\n### Probable root cause\\n\\nThe install script was hardened to download and verify a SHA256 `checksums.txt` from the same GCS prefix as the binary tarball. The pinned `ENGINE_VERSION=1.0.2-6113393518706688` is a prerelease build whose GCS layout does not include `checksums.txt` (the directory only contains the `linux-x64/`, `darwin-arm/`, etc. tarball folders). The new hardening step has no compatible asset for the pinned version.\\n\\n### Proposed remediation (any one is sufficient)\\n\\n1. **Publish `checksums.txt`** to `(antigravitypublic/redacted) with the existing tarball SHA256s, so the current script works unmodified.\\n2. **Pin `ENGINE_VERSION` to a release that already publishes `checksums.txt`** (e.g., the next public Antigravity CLI release) and update `actions/setup/sh/install_antigravity_cli.sh` consumers accordingly.\\n3. **Make the checksum step tolerant**: if `checksums.txt` returns 404, log a warning and skip checksum verification (still safe because the tarball is fetched over HTTPS from the same GCS origin). Keep strict verification when the file is present.\\n4. **Revert the checksum verification step** until option 1 or 2 lands, restoring the previously-working code path (direct tarball download).\\n\\nRecommended path: **option 1** (publish `checksums.txt`) — it preserves the security hardening and unblocks PR smoke immediately. Option 3 is a good safety net if checksum publishing cannot be guaranteed on every internal prerelease build.\\n\\n### Success criteria / verification\\n\\n- A new `Smoke Antigravity` PR run completes `Install Antigravity CLI` step with `✓ Checksum verification passed for cli_linux_x64.tar.gz` (or the warned-skip path if option 3 is taken).\\n- The agent step proceeds past `Install Antigravity CLI` (no `exit code 22`).\\n- No 404 on `${GCS_BASE_URL}/${VERSION}/checksums.txt` for the currently pinned `ENGINE_VERSION`.\\n- Verify on at least one PR rerun before closing.\\n\\n### References\\n\\n- Parent: [#35484](https://github.com/github/gh-aw/issues/35484)\\n- Failing run: [§26639071214](https://github.com/github/gh-aw/actions/runs/26639071214)\\n- Last successful run: [§26609936898](https://github.com/github/gh-aw/actions/runs/26609936898)\\n- Script: `action