Specifies synchronization, persistence, history, consistency, observability, and recovery for watchers. This reference fixes the adoption boundary, failure behavior, and observable evidence while leaving 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 Watchers, adopt a durable operation log with explicit version and participant identity. Use one owned boundary, explicit state model, and versioned interfaces; keep policy decisions separate from adapters and side effects. 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 Watchers actors, inputs, outputs, states, policy or schema versions, and externally visible outcomes described by this architecture 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
- Assign every durable mutation an operation identifier, actor, base version, server version, and authorization context.
- Choose one conflict strategy per data type and make merge, rejection, and manual-resolution outcomes visible to participants.
- Treat presence and typing indicators as ephemeral hints; never use them as proof of ownership, approval, or a durable edit.
- Preserve an append-only history of material changes even when the current projection is compacted or rebuilt.
- Document component ownership and allowed dependency direction, including which data may cross each boundary.
- Make synchronous, asynchronous, and batch paths implement the same authority and state invariants.
- Represent watching as a durable scoped subscription with subject, target, event classes, origin, state, preference version, and history rather than inferring it from recent activity.
- Authorize target visibility at subscription and delivery time, deduplicate notifications, and handle mute, removal, blocking, target deletion, and permission loss explicitly.
Implementation guidance
- Start with the domain state and interface contract, then attach adapters, storage, queues, and provider-specific code.
- Model Watchers inputs, outputs, actors, states, invariants, side effects, and evidence before selecting framework or vendor details.
- Store the applicable Watchers 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
- Disconnected or stale clients keep recoverable local intent and resynchronize from a durable version before issuing further writes.
- Invalid or contradictory Watchers 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
- Exercise the contract through each adapter and prove that a failed dependency cannot bypass the authoritative boundary.
- Monitor Watchers 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.