scrollport is a reliability and payment layer for provider-backed catalog tools. An agent gets one key and one wallet; the catalog grows behind a stable four-control-tool surface.

## The platform boundary

The public catalog has four useful levels:

1. A **category** groups a broad kind of work.
2. A **capability** is the provider-neutral job an agent wants done.
3. A **provider** supplies one or more implementations.
4. A **catalog tool** is the smallest independently discoverable, inspectable and executable operation.

`discover` returns the first three levels plus bounded catalog-tool alternatives. `inspect` reveals the current contract for one selected tool. The human view of that tool lives under [/tools](https://scrollport.com/tools); the agent view is `inspect(tool_id)`.

## One fixed control surface

The MCP server exposes exactly four control tools:

- `discover` searches the live public catalog by outcome.
- `inspect` returns the selected catalog tool's current input and output contract.
- `run` validates, holds, executes and settles one operation.
- `wallet` reports balance, held funds and available spend.

Catalog tools are data returned by `discover`, not hundreds of permanently loaded definitions. Adding a catalog tool does not require a client to learn a new MCP name.

## Human approval stays at the boundary

Device authorization is a browser ceremony. The agent asks; the human sees the request and approves it. Provider connections are also human-owned. An agent can explain that a connection is required and pass along `connect_url`, but it cannot receive or manage the provider credential.

## The money path

Before a paid run, scrollport validates the input and calculates an estimate. The ledger places a hold, the worker executes the catalog tool, and settlement captures the actual amount while releasing the difference. If the run fails, its full hold is released. An estimate over the account threshold becomes an approval request instead of an execution.

## The live catalog boundary

Only published, live and unarchived catalog tools appear in discovery. A provider can be available while a particular listing is unpublished or degraded. That distinction keeps the public catalog honest and prevents documentation from becoming a second, stale catalog.