Add unit coverage for the encrypted at-rest egress secrets: the
secret_store round-trip (new_env_var_secret/encrypt_value/decrypt_value)
and the registry/service wiring that injects ENV_VAR_SECRET.
Recovered from the bot-bottle-claude-agent-1 VM after the CI runner's
disk filled and forced its rootfs read-only; committed work was already
on origin, these were the agent's uncommitted changes.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
