* fix(nix): replace magic-nix-cache with Cachix
magic-nix-cache caused recurring CI failures (TwirpErrorResponse
ResourceExhausted) by hitting GitHub Actions Cache's 10 GB limit and
200 req/min rate limit. This was flagged as 'unfixable infra flake' in
#17836 but is actually a fixable architecture choice.
Switch to Cachix (dedicated binary cache, no GHA quota dependency):
- Replace DeterminateSystems/magic-nix-cache-action with cachix/cachix-action
- Add cachix-auth-token input to nix-setup composite action
- Pass CACHIX_AUTH_TOKEN secret through all three nix workflows
- continue-on-error: true so cache failures never block CI
Cache 'hermes-agent' is public at hermes-agent.cachix.org.
Devs can pull locally with: cachix use hermes-agent
* fix: correct cachix-action commit SHA pin
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Co-authored-by: Hermes Agent <hermes@nousresearch.com>
