Web-standard server handler

createChatHandler mounts one shared chat definition behind the platform Request, Response, ReadableStream, and AbortSignal APIs.

For deterministic misses that need cited semantic retrieval, use the sibling createAskServiceHandler. Both handlers use Web standards; the Ask vertical additionally resolves a complete trusted site policy and shares one public request/configuration contract across hosted and self-hosted deployments.

const handleChat = createChatHandler({
  authenticate: async request => {
    const identity = await verifyBearer(request)
    return identity
      ? { ok: true, context: identity }
      : { ok: false, response: new Response('Unauthorized', { status: 401 }) }
  },
  resolveDefinition: context => chats.forTenant(context?.tenantId),
  sessionStorage: context => sessions.forTenant(context?.tenantId),
  timeoutMs: 30_000,
})

Send an encoded client.turn.submit event as application/json. A successful response is application/x-ndjson; every line is an encoded turn event and can be passed to decodeTurnEvent and a session-bound snapshot cursor.

Authentication completes before parsing untrusted JSON. Trusted context exists only in the host closure and is never read from the submit payload. Return a host-owned response for authentication failures.

Canonical messages remain in definition.chat.memory. Application metadata uses the CAS SessionStorage contract. The handler waits for the final canonical message save before closing a successful response.

sessionStorage is required because the persisted cursor, active-turn lease, and latest 64 terminal turns prevent sequence rollback, concurrent execution, and recent sequential replay of model/tool effects. Terminal outcomes distinguish completed from indeterminate when canonical memory could not be saved. The handler claims the turn through CAS before creating the controller and releases it only after bounded cleanup. State updates are coalesced to the latest full snapshot under backpressure.

The default body limit is 64 KiB and deadline is 30 seconds. Method, media type, body, event, timeout, cancellation, and internal failures use safe versioned diagnostics. Request abort, response cancellation, and timeout stop the upstream AgentsKit controller/source.

Deployment

• Next/Remix/SvelteKit/edge: export the returned handler directly where Web handlers are supported.
• Node HTTP: translate the incoming request to Request and pipe the returned Response.body; the package test contains a reference bridge.
• Express/Hono adapters should remain thin and must forward disconnect cancellation.

Semantic Ask backend

createAskServiceHandler authenticates and resolves site identity before body parsing, treats client corpus/persona parameters only as equality-checked compatibility hints, and injects the trusted site policy into local or federated AgentsKit retrieval. A successful answer always includes at least one safe citation. Rate limiting, provider generation, CAS storage, and telemetry are host adapters rather than bundled infrastructure.

See the complete backend guide and ADR-0026.