@expo/snapback-app-cli

@expo/snapback-app-cli provides the snapback-app command: an agent-facing terminal over one generated Snapback application. It discovers operations from digest-verified artifacts or a served API envelope, validates argument contracts, and can introspect, call, subscribe, emit types, or run bounded code mode without importing application source.

This package is optional. Install it directly when an agent or automation needs the generic application-data terminal. Use @expo/snapback-cli for project creation, codegen, the development server, testing, administration, and deployment; snapback-app does not replace that lifecycle CLI and carries no ambient admin authority.

Inspect and call an application

In an existing Snapback application, add the optional package and generate the backend artifacts first (the application already carries snapback through @expo/snapback-cli):

npm install --save-dev @expo/snapback-app-cli
snapback generate snapback
snapback-app --artifacts ./snapback/generated introspect

introspect is the safest first step. It emits a bounded, value-free digest of the app's schemas, operations, capability facts, and gaps. It does not import the generated API module or handler bundle.

To call a function on a running local target, choose authority explicitly and replace listTodos with a name returned by introspect:

snapback-app \
  --server http://127.0.0.1:4287 \
  --artifacts ./snapback/generated \
  --principal dev \
  --dev-user user_ada \
  --args-json '{}' \
  call listTodos

Anonymous is the default even when credential material exists. Session and agent lanes require explicit file-backed custody. The shipped engine is a local-target surface; hosted targets do not currently advertise the app-CLI capability.

Documentation outside a checkout

A running Snapback server serves the Guide compiled into that exact build. These links use the first default development port; use the origin printed by snapback dev or snapback start if yours differs.

• Follow the app CLI guide for introspection, principals, subscriptions, pairing, and code mode.
• Read generated artifact custody for the files this command trusts.
• Read first: the start packets — the budgeted per-template first read (LLP 0259).
• Look up (do not linear-read) the capability index for the current local and hosted claim boundary.
• Run snapback guide or snapback guide <query> to browse or search the embedded Guide.
• Run snapback mcp for the same build-bound corpus as read-only MCP resources, starting at snapback-guide://manifest.

Operate it

snapback mcp serves read-only Guide resources; snapback mcp-control adds typed control tools with local admin authority. Preview control setup with snapback agent setup --print <client> --server mcp-control.