> ## Documentation Index > Fetch the complete documentation index at: https://docs.vendo.run/llms.txt > Use this file to discover all available pages before exploring further. # Handler options: createVendo config and fetch settings > Every createVendo configuration option and fetch-handler setting, including base path, principal resolution, CSRF policy, and wire error behavior. ## Composition configuration | Option | Required | Behavior | | ------------ | ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `model` | yes | AI SDK `LanguageModel` used by the agent and default app generation | | `principal` | yes | resolves the host request to a principal; `null` creates an ephemeral session | | `store` | no | defaults to PGlite at `.vendo/data` | | `sandbox` | no | unlocks app rungs 2 through 4; absent means rung 1 only | | `catalog` | no | `ComponentCatalog` of host components exposed to the generation prompt; merged with any `.vendo/catalog.json` written by `vendo sync`, with explicit entries winning by name — see [Host components](/connect/host-components) | | `connectors` | no | adds external connector tool registries | | `actAs` | no | supplies scoped auth material for away host API execution — see [actAs presets](/connect/act-as-presets) | | `policy` | no | policy file, rules, directions, and code escape hatch | | `judge` | no | contextual guard judge | | `secrets` | no | defaults to environment-backed secret lookup | | `telemetry` | no | wires build and development telemetry | | `mcp` | no | opens the [MCP door](/capabilities/mcp) so outside agents reach host tools through the guarded path; `true` for defaults, or an object carrying `{ baseUrl?, remoteAs?, federation? }` when door-specific settings need to flow through the umbrella (see [Configure the door through the umbrella](/capabilities/mcp#configure-the-door-through-the-umbrella)); off by default | | `oauth` | conditional | `HostOAuthAdapter` used by the door for session lookup and principal resolution; required when `mcp` is enabled. The door renders consent when the adapter uses `session`, or hands off the whole page when it supplies `authorize` instead — see [MCP door](/capabilities/mcp) | | `remoteAs` | no | delegates MCP bearer authentication to an external ES256-signing authorization server (`{ issuer, audience, jwksUri? }`); disables the door's local OAuth endpoints. Also accepted under `mcp: { remoteAs }` — see [MCP door](/capabilities/mcp) | | `federation` | no | enables the `/api/vendo/mcp/federate` handshake so an external authorization server can borrow the host's login flow; takes a shared `{ secret }`. Also accepted under `mcp: { federation }` — see [MCP door](/capabilities/mcp) | | `agent` | no | chat context controls: `toolOutputCap`, `maxOutputTokens`, `historyWindow` (see [Agent context](#agent-context)) | ## Agent context Pass an `agent` block to tune what the chat loop sends to the model. All fields are optional. ```ts theme={null} createVendo({ model, principal, agent: { toolOutputCap: 32_000, // char cap per tool result before it reaches the model; 0 disables maxOutputTokens: 4_000, // upper bound on tokens the model may emit per turn historyWindow: 20, // last N whole messages re-sent per turn; omit to send the full thread }, }); ``` * `toolOutputCap` caps a single tool result before it reaches the model, so a runaway host response can't blow the context window. Defaults to `32000` characters. Pass `0` to disable the cap. Persistence and the streamed thread are unaffected — only the copy sent to the model is truncated. * `maxOutputTokens` bounds tokens the model may emit per turn. Omit to defer to the model default. * `historyWindow` bounds how many past messages are re-sent to the model each turn. Vendo keeps whole messages so tool-call/result pairs stay paired. Omit to send the full thread (current behavior). The stored thread is untouched; only the per-turn model context shrinks. ## Base path The wire mounts under one base path, default `/api/vendo`. Configure `createVendoClient({ baseUrl })` when mounting elsewhere. Rung 4 HTTP app UI is not proxied through this base. ## Identity Every wire request passes through `principal(req)`. The returned `Principal.subject` scopes threads, apps, approvals, grants, activity, and runs. Ephemeral principals never write to disk. `principal(req)` must return `kind: "user"` (or `null`). Returning `kind: "org"` or a subject that starts with `vendo:` is rejected at the wire — those identities are Vendo-owned. See [Principals and organizations](/deploy/principals-and-orgs). When `principal(req)` returns `null`, Vendo issues an anonymous session cookie. The first authenticated request afterward merges the anonymous session's threads, apps, and state into the signed-in user; grants, approvals, connected accounts, and history stay put. ## CSRF floor Cookie-authenticated state-changing requests require `Content-Type: application/json`. The exhaustive exceptions are binary `/apps/import`, signed `/webhooks/:source`, and bearer-authenticated `/tick`. ## Error envelope Every non-2xx response has this shape: ```json theme={null} { "error": { "code": "validation", "message": "Readable message" } } ``` The fixed map is `validation` 400, `not-found` 404, `blocked` 403, `conflict` 409, `cloud-required` 402, and `sandbox-unavailable` or `not-implemented` 501. MCP door paths are the exception; they speak MCP and OAuth response shapes.