ci: prefetch the Docker test image from ECR Public

[jbeckwith-oai]

CI currently lets Docker sandbox tests implicitly pull python:3.14-slim from Docker Hub. Anonymous pull limits have repeatedly failed Node tests and coverage, including #2060 and main. Add an explicit image-preparation step before dependency installation in the Linux test matrix and coverage job.

Pull the Docker Official Image from ECR Public, pinned to index digest sha256:a2b82f3c48559aa0a8446d9af49826b6e2b2016f4cd2afabfe6013ec53729170, and tag it locally as python:3.14-slim for the unchanged tests. Docker Hub and ECR returned byte-identical index manifests during verification. Pull failure stops the job at setup. No credentials, permissions, test skips, SDK defaults, Windows behavior, or docs-only gating change.

Validation: actionlint passed; four shell probes verified successful pull/tag ordering and fail-fast behavior in both job definitions; scoped secret scan reported zero detections (local process-inspection cleanup emitted a sandbox warning); two independent review rounds found no issues. Hosted CI will validate the actual mirrored pull and complete suite. This pin needs periodic reviewed refreshes for Python/base-image security updates; the existing Dependabot configuration does not automatically update it.

Maintainer/security review requested for the CI image-source change. This one-file PR is independent of #2060 and can merge first to restore CI reliability. It does not change the separate Actions PR-creation/approval setting.

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Latest commit: 79ca786

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-09T22:36:33.000054Z	79ca786	PR opened
🔒 Security Review	✅ Completed 2026-10-09T22:36:44.309738Z	79ca786	PR opened

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[markstuart-oai]

Reviewed 79ca7866504f504f8858df85f1242ac61b5314bc. Both Linux jobs pull the fixed digest, then tag it for the existing Docker tests. Setup fails before tests if pull or tag fails. Permissions, credential handling, Windows behavior, and docs-only conditions are unchanged. The existing runtime uses the local image tag without forcing another pull. I found no actionable issues.

I independently fetched the Docker Hub and ECR index manifests: their bytes are identical and match the pinned SHA-256. Hosted Node 22/24 and coverage jobs pulled that digest and executed the Docker tests. Each reported 7,834 passing and 32 skipped tests; coverage thresholds passed. No Docker commands, builds, or tests were run locally. The pin still needs the reviewed refreshes noted in the PR.