[kim-em]

TauCeti cache restoration can fall back to compilation after an artifact download fails, aborting regeneration even when dependency pins are correct. Interrupted single-file downloads can also leave partial cache entries.

Use verbose cache-only restoration with one whole-step retry, plus a curl wrapper with bounded download retries, connection/stall/transfer limits, and atomic publication. Preserve complete diagnostics on failure and export the wrapper for subsequent trusted builds.

Validation: all 62 benchmark Python tests pass with the real-Lake test enabled, including HTTP/partial-transfer tests and a real-Lake restoration fixture. The fixture proves an interrupted transfer leaves no partial cache artifact and an unchanged-cache retry restores and imports the module without compilation. Script-level tests cover restoration retry/exhaustion, export propagation, and the existing pin mismatch guard. A dedicated CI workflow runs the new tests. Full pinned TauCeti restoration also passed locally in cache-only mode (14,602 jobs, no TauCeti compilation). Bash syntax, workflow lint, action-pin audit, and diff checks pass.

Depends on leanprover/lean-eval-submissions#2156 for the optional CURL export. Merge that PR first.

Refs leanprover/lean-eval-submissions#1894.

[kim-em]

Please merge leanprover/lean-eval-submissions#2156 first. This PR exports CURL alongside the cache settings so subsequent trusted builds also get atomic downloads and retries; the submission-pipeline change accepts that optional export while retaining its own trusted wrapper.