Verify cache seed publication without coupling deploy smoke jobs #433

Description

Cache smoke jobs can report successful seeding when cache-service throttling prevented publication, causing later reuse probes to fail without explaining the seed failure. Move the cache-seed hardening from PR #403 into a focused change against main.

Done when

• Compiler seed publication is verified with bounded retries and confined cleanup.
• Target seed publication is verified with a bounded retry and fails closed on exhaustion.
• Deploy release and smoke jobs remain independent of cache probe availability.
• Regression tests cover successful, transient, permanent and compile-error cases.

Affected area

CI / Tooling