[B2B Feature]: Expose microsite creation and link minting as MCP capabilities

[anfibiacreativa]

Describe the problem

Sellers also work in external assistants (chat/productivity tools), not only the in-product assistant. The same microsite-creation and link-minting capability should be reachable from those surfaces.

Propose a solution

Expose the stream's steps (recommend, author, register access-control, mint link) as reusable capabilities so external assistants can invoke the same flow, keeping the in-product build and the external build on one implementation.

Flow

1. External assistant receives a brief.
2. It invokes the shared capabilities to author + gate the microsite.
3. It mints and returns a shareable link.
4. The seller shares the link with the customer.

Associated skill

Shared capabilities used by the in-product skill.

Affected blocks / pages

Capability/tool layer shared across surfaces.

Analytics data involved

Same report/analytics inputs as the in-product flow.

Priority

Nice to have

Additional context

Part of epic #112. EPA-4 (external microsite creation). Build steps MCP-shaped so this reuses the same implementation.