Activity feed: Concurrency, audit, and operations

Specifies synchronization, persistence, history, consistency, observability, and recovery for activity feed. 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 Activity feed, 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 Activity feed 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.
• Build the feed as an authorized projection of immutable activity identities, actors, targets, verbs, audience, occurrence time, and source version rather than as copied display text.
• Define stable ordering, cursor pagination, deduplication, grouping, edits, tombstones, and backfill behavior while rechecking current visibility before every read.

Implementation guidance

• Start with the domain state and interface contract, then attach adapters, storage, queues, and provider-specific code.
• Model Activity feed inputs, outputs, actors, states, invariants, side effects, and evidence before selecting framework or vendor details.
• Store the applicable Activity feed 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 Activity feed 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 Activity feed 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.