Desktop Driver MCP agent instructions

This package is the Model Context Protocol adapter for the Desktop Driver agent operations. It is the instruction root for this package and every descendant.

Start here

Read the README, then the narrowest entry in the reference index. The operations themselves, their schemas, and their failure reasons belong to @fluentui-react-native/desktop-driver (its agent operations reference); this package only maps them onto MCP.

Invariants

• Stay a thin client. Every tool calls the service's operation routes through the typed client; never add a second execution path, a host, or state the service does not own. Tool input schemas come from the driver's registered operation schemas, so the service and the adapter cannot drift apart.
• stdout carries MCP protocol only. Diagnostics go to stderr. Never log the grant, the descriptor contents, or application text.
• Connect only through a private connection descriptor, verified by the installed native helper before the grant is sent. Never launch or build the service or a helper, and never accept a URL or grant from a command line, environment variable, or the model.
• Serialize acquisition, use, close, and disposal per MCP connection. Retain cleanup responsibility after transport loss; reverify discovery and never replay a failed mutation. A verified replacement invalidates old references. Fence a lost acquisition response; disposal also cleans up late acquisitions.
• Delegate a distinct driver-only child after verified discovery. Retain it on same-incarnation/descriptor-principal rediscovery; never share or resume another connection's session. Disposal awaits child revocation, keeping terminal-only cleanup proof for lost responses and failed drains; unauthorized is not cleanup.
• Tie every artifact link to its session. Artifact ids restart in each session.
• Progress ticks come from the adapter and never reach the service, so a waiting model does not keep an idle session alive. Cancellation aborts the HTTP call, which the service treats as the caller leaving.
• Messages the model reads are fixed or bounded. Connection failures use fixed diagnostics on stderr too; never echo discovery exceptions or descriptor contents.

Validation

Run yarn format, yarn lint, yarn build, and yarn test in this package. Changes to tool schemas also need the tool-list size bound in src/server.test.ts to hold. A change to driver operations is validated in the driver package first. JavaScript tests use the fake host and are not native qualification; record a live run against a real application for native claims. Add a patch changeset for this published package when its behavior or shipped guidance changes.