CI flake - sccache server connection refused

Detected by CI Gremlin after a failed GitHub Actions attempt succeeded on rerun.

Tests:

Error:
error: could not compile libc (build script)
2026-10-27T20:20:14.8086273Z

Failed job runs:

Timeout detection:

Context:

Symptoms and root cause

Exact failed job 122446016234, run 40576457694, attempt 1, Test Suite - C++ Compile (indexes): Run C++ compile tests failed on the Linux self-hosted runner at 2026-10-27T20:20:14Z.
Primary diagnostic: sccache: error: Connection to server timed out: Os { code: 111, kind: ConnectionRefused, message: "Connection refused" }. The sccache-wrapped Rust compiler exited 2 while building libc v0.2.190's build script; Cargo then exited 101. could not compile libc is downstream, not evidence of a libc source defect or C++ assertion failure.
The subsequent statistics command worked but reported zero compile requests/executions. Why the cache server connection was unavailable is not established by these logs. The earlier apt repository-signature warning did not stop setup.
Attempt 2, job 122772639827 succeeded.

Searched open issues only for sccache, ConnectionRefused, Connection refused, server timed out, could not compile, libc, and the C++ compile job name, including sccache mentions in comments.
Closest open infrastructure candidate CI flake: sccache failed to start: cache storage failed to read: Unexpected (temporary) at read => send http request #5557 has one actual incoming canonical duplicate relationship, verified on its complete open-root timeline. Its diagnosis is specifically a GitHub Actions cache-backend DNS lookup failure during server startup; this attempt instead uses a local-disk cache and reports connection refusal without that backend/DNS diagnostic. Available evidence does not establish the same specific failure, so no duplicate closure is proposed. Other search hits concern unrelated compiler crashes, runner/matrix mismatch, or test assertions.

Keep open. No supported specific open duplicate was found.
Proposed title: CI flake - sccache server connection refused during C++ compile setup — names the earliest informative diagnostic rather than blaming libc.
Proposed team: DevOps — compiler-cache/runner infrastructure, not an observed product test failure.
DRY RUN: title and team changes are proposals only; no issue metadata, state, or duplicate relationship was changed, and no existing issue was modified.