Summary

• in the direct single-cache daemon path, surface non-NotFound remote read failures through the existing cache-error statistics path instead of counting them as ordinary misses
• make post-CompileStarted response I/O failures follow the documented default-fatal policy while preserving SCCACHE_IGNORE_SERVER_IO_ERROR=1

Deliberately unchanged

• startup rate-limit tolerance
• automatic read-only downgrade when a configured backend cannot write
• explicit read-only and public-cache configurations
• client-side IPC and multi-level cache fallback policies

Scope

One commit changes src/cache/cache.rs and src/commands.rs only. There are no documentation, protocol, cache-format, dependency, disk-cache, multi-level-cache, or client-side-storage changes. Existing documentation already describes the server-I/O policy.

Validation

Focused regression tests cover unexpected direct remote read errors, default-fatal post-start disconnects, and the existing opt-in local fallback. Upstream CI and maintainer review remain required before merge.