Backend Client Standard

Backend integration uses centralized transports and feature-scoped semantic clients. This is an application-client capability, not an activity or web requirement. Web, native, CLI, worker, and local tools may adopt it.

default_backend_integration_standard

Returns the centralized backend-client capability rules.

render_backend_integration_standard

Renders the backend-integration capability as text or JSON.

Layering

Generated contract projections own wire shapes and boundary decoding.
Shared transports own URLs, headers, credentials, deadlines, retries, streams, and sockets.
Feature clients expose semantic operations in domain language.
Stores own feature state and authoritative snapshot application.
Workflows compose operations and cancellation.
Components render state and report user intent.

Transport Selection

Transport	Use	Avoid when
HTTP	Finite commands, queries, snapshots, uploads	Both peers need ongoing messages
SSE	Server progress and event streams with browser reconnection	The client must send stream messages
WebSocket	Bidirectional or latency-sensitive protocols	Request/response or one-way events are sufficient
Polling	Simple infrequent status refresh	Latency or request volume makes it wasteful

Request Policy

Normalize transport, protocol, authentication, validation, conflict, and cancellation errors.
Every operation has an explicit deadline or documented long-running policy.
Callers can cancel work; frame or process shutdown propagates cancellation.
Retries belong to the transport or semantic operation that understands idempotency.
Mutating retryable operations use an idempotency key or equivalent deduplication contract.

Streaming Policy

A stream defines protocol version, event identity, ordering, correlation, replay or resume token, heartbeat, backpressure behavior, reconnect/backoff, terminal events, cancellation, and authoritative resynchronization. A queryable snapshot is the recovery authority after missed or invalid events.

Local Applications

Loopback HTTP does not imply trust. Local web applications document origin allowlists, authentication or capability tokens, CSRF posture, port discovery, protocol versions, process ownership, startup readiness, and shutdown behavior. Native IPC may implement the same semantic-client interface without leaking its transport into workflows.

Audit Boundary

Dev-std validates declared transport, feature, source, and signoff paths. Project lint validates forbidden raw transport construction and dependency direction. Tests exercise normalized failures, cancellation, retries, reconnect, resynchronization, and protocol-version mismatch.

Executable Evidence

The canonical implementation evidence lives in docs/templates/web/lit-activity/src/transport/ and the feature-scoped project client. It demonstrates a replaceable demo/HTTP transport boundary without allowing activities or views to construct raw network requests. Clean-copy validation and maintainer commands are documented in Build Documentation.