[CI] Retry CPU image builds after truncated network streams

[khluu]

Summary

• classify truncated Git/HTTP stream failures as transient in the CPU image build retry loop
• cover GitHub clone disconnect/early-EOF/index-pack failures and interrupted LLVM downloads
• preserve the existing four-attempt limit and 10/20/40-second backoff

Why

Main builds #88996 and #88997 lost six CPU jobs on one physical host before tests. Five image builds ended while cloning triton-cpu with HTTP/2 stream cancellation followed by fetch-pack disconnect, early EOF, and invalid index-pack output. The sixth lost its LLVM archive stream with BrokenPipeError: [Errno 32] Broken pipe.

run-cpu-test.sh already retries transient image-build network errors, but none of those concrete transport signatures matched BUILD_RETRY_PATTERN, so every affected job exited after attempt 1 instead of using the existing bounded retry policy. The exact PR build for each merged change had passed the relevant lanes, and these failures are unrelated to either source diff.

Duplicate check

Searched open PRs and issues for CPU build retry HTTP/2 early EOF, triton-cpu unexpected disconnect retry, and CPU CI triton clone early EOF; no existing fix was found.

Tests

• bash -n .buildkite/scripts/hardware_ci/run-cpu-test.sh
• matched all five observed transport signatures against the amended pattern and verified a representative compiler error does not match
• uvx --from shellcheck-py shellcheck .buildkite/scripts/hardware_ci/run-cpu-test.sh
• PRE_COMMIT_HOME=/tmp/sherlock-precommit-cpu-retry uvx --python 3.12 pre-commit run --files .buildkite/scripts/hardware_ci/run-cpu-test.sh
• git diff --check

No model evaluation is applicable; this changes CI retry classification only.

This draft was prepared with AI assistance. A human submitter must review every changed line and validate the retry behavior before marking it ready.

[khluu]

/ci run

[github-actions]

✅ Triggered Buildkite CI #89003 for commit 7b962d3f2c21.

[khluu]

Closing this duplicate draft: the existing draft #56597 already owns CPU image-download retry classification. I will fold the newly observed HTTP/2 clone-disconnect signatures into #56597 instead.