Provides contract tests, mocks, telemetry, health checks, debugging guidance, and operational acceptance criteria for external API fallback. It fixes adoption boundaries and observable failure evidence while keeping environment-specific limits configurable.
Package status: reference context ready for human review. The contract and test scenarios are complete, but no claim is made that an adopting implementation has passed them.
Decision
For External API fallback, adopt a versioned wire contract at the service boundary. Treat the block as a release and regression contract built from representative positive, boundary, denial, failure, and recovery cases. This package is a reference contract: the adopting team must choose numeric limits, providers, jurisdictions, and operational owners from evidence in its own environment.
Scope
- The External API fallback actors, inputs, outputs, states, policy or schema versions, and externally visible outcomes described by this testing block.
- Primary and alternate interfaces, background work, caches, integrations, support paths, and evidence that can exercise the same boundary.
- Adoption-specific configuration, rollout, recovery, and verification responsibilities needed to apply the reference safely.
Outside this block
- Choosing a universal vendor, framework, jurisdiction, numeric threshold, retention period, or service-level objective for every adopter.
- Claiming that packaged scenarios have run against a downstream implementation or that this reference grants legal, security, or accessibility certification.
Contract
- Define request, response, error, pagination or event semantics independently of one client implementation.
- Authenticate the caller and authorize the resource and action on the server before returning data or accepting work.
- Use explicit timeouts, bounded retries with jitter, and a terminal outcome; do not retry non-idempotent effects blindly.
- Carry a correlation identifier through the integration while excluding credentials and sensitive payloads from telemetry.
- Record fixture version, environment, configuration, observed result, and evidence location for every decision-bearing run.
- Separate product failure, dependency failure, test-infrastructure failure, and inconclusive evidence in reports.
- Declare which fields are authoritative, optional, or stale-tolerant before permitting fallback; required or sensitive fields fail the aggregate closed.
- Do not combine results from providers with incompatible identity, freshness, entitlement, or units without an explicit normalization contract.
Implementation guidance
- Build the smallest deterministic fixture set that spans risk classes, then add production-derived cases only after privacy-safe review.
- Model External API fallback inputs, outputs, actors, states, invariants, side effects, and evidence before selecting framework or vendor details.
- Store the applicable External API fallback contract or policy version with material state so migrations, replay, and support decisions remain attributable.
- Introduce the path behind controlled rollout, compare expected and observed outcomes, and keep a tested recovery route until adoption evidence is complete.
Failure handling and safeguards
- Dependency failure maps to a stable error or fallback state; ambiguous side effects are reconciled before another attempt.
- Invalid or contradictory External API fallback state is rejected or quarantined; the implementation never guesses a value that broadens authority or duplicates an effect.
- Retries are bounded and use durable identity; after exhaustion, work reaches an inspectable terminal state with an accountable owner.
Verification and operations
- Run the suite twice from a clean state and confirm that ordering, retries, and parallel execution do not change the verdict.
- Monitor External API fallback success, denial, validation failure, dependency failure, retry exhaustion, and recovery by contract version without sensitive payload dimensions.
- Re-run paired positive and negative fixtures after policy, schema, dependency, migration, or boundary changes and preserve the resulting evidence.
Adoption assumptions
- Names and values in the example are a concrete fixture, not universal defaults; adopters replace them through documented evidence and ownership.
- The adopting system can provide authenticated identity, durable operation or record versions, bounded telemetry, and a controlled path for change.
The executable-looking examples in this package are fixtures and acceptance contracts. Run the collection validator to check structure and metadata, then translate and execute the scenarios in the target repository before recording implementation evidence.