ADR-0002: Configuration Resolution - No Merging

Status

Accepted

Context

Configuration systems often layer multiple sources (config files, env vars, CLI args, defaults) with complex merge semantics. This creates:

• Non-deterministic behavior depending on environment
• Hard-to-reproduce bugs in CI vs production
• Implicit coupling to deployment environment
• Test fragility (tests affected by host env vars)

Decision

Config-as-code has absolute priority. No merging, no env var overrides.

Resolution rules:

1. If RegistryConfig is provided in code → use it exclusively
2. If no config is provided → environment variables may be used as a fallback
3. No layering, no merging between sources
4. Backend defaults apply last (within a single config source)

Consequences

• Deterministic: same code = same behavior, regardless of environment
• Test-safe: no env var leakage into tests
• Explicit: configuration is visible in code, not hidden in env
• Trade-off: slightly more verbose config for pure-env deployments (acceptable — those users can build their own config loader and pass RegistryConfig)