Connect tools to host data

Let Eve tools access application data without trusting model-selected identities.

Application tools execute in the Eve runtime but must preserve the host authorization boundary.

The host saves a message with trusted scope and subject identifiers.
The host sends only bounded, non-authoritative context to the Eve session.
A tool derives its authority from verified Eve session context, never model input.
The tool sends an authenticated, narrowly scoped request to a host HTTP action.
The host re-verifies the invocation and calls an internal Convex function.

Never accept userId, scopeId, or equivalent authority from model tool input.

The example currently uses deterministic fixtures and authenticates the Convex-to-Eve transport as one service principal. End-user identity forwarding and a supported host-tool client are planned before production application tools are enabled.