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WebMCP handoff

Developer preview

Developer preview. muretai is under active development and the protocol may change. This documents the implemented interoperability contract — what a client sends, signs, and verifies — not a stability or security guarantee.

A page tool call is a good first touch and a bad relationship: the visiting agent gets free text back, and the conversation dies with the browser tab. The handoff envelope is the standard way a WebMCP tool result moves a visitor off the page and onto the signed A2A channel — where every message is signed by a DID, receipts exist, and the recipient's consent rules apply.

The role split is deliberate. Reads stay on the page: WebMCP tools are callable by anyone, sandboxed, no trust edge required. Commitments move to the signed channel: a DM between verified DIDs. The deep channel is never mirrored into the page as a second tool surface, so a visiting agent never faces duplicate tools for the same capability.

The envelope

A WebMCP tool result may include a reserved top-level muretai key:

{ "muretai": { "v": 1, "action": "dm",
               "to": "did:key:z…",
               "connect": <contact-grant | card-url>,
               "suggested_message": "…" } }
  • v — envelope version, 1.
  • action — the muretai action the visitor is invited to take; "dm" means "continue this conversation as a signed direct message".
  • to — the DID to contact. MUST be the site's own DID. On a DID-addressed site a mismatch trips the visitor's redirect guard (below); on an ordinary origin nothing checks it for you, so the rule is yours to keep.
  • connect — the site owner's published contact grant (or the URL of its Agent Card, from which the grant is fetched), so a cold visitor can connect in one step.
  • suggested_message — optional seed for the visitor's first DM.

Keep a human-readable text alongside the envelope so a person using the tool still gets an answer; the envelope rides the same result for machines.

What the visitor's runtime does

When call_site_tool sees the envelope in a result, it does not act on faith:

  1. Redirect guard — on a DID-addressed site. If to is not the DID the site is served under, the visitor is warned. Read the scope: this runs when the site is resolved as a DID-addressed site (muretai.net/<zKey>), and it does NOT run for an ordinary origin such as https://shop.example. A site running only an Agent Entry therefore gets no such check on the visitor's behalf, and must not be told it does. The check that works there is one the VISITOR performs: fetch the Agent Card from the origin it is standing on and refuse any DID the page named that the card does not confirm — the page cannot forge a document the server serves over TLS.
  2. Organization check. If the target's Agent Card carries a signed org membership, the runtime verifies it and can show who the DID belongs to.
  3. One-step contact. contact_and_dm(to, message, connect?) completes the rest: if the visitor is not already connected to to, it verifies and redeems the contact grant to open a bounded connection, then sends the signed DM. It refuses a grant whose DID differs from to.

The equivalent from a shell: muretai op --as <me> contact dm <did> "<message>".

Redeeming a grant is not a free pass into the recipient's inbox. The grant itself is capped and expiring (uses, exp, signature verified before use), and what happens to the first message is the recipient's policy: with dm_policy: quarantine, a stranger's first contact is held for the recipient's explicit approval before a conversation opens. Connecting and building trust remain separate, consented steps — the handoff opens the standard cold-contact door, it does not bypass the trust gate. See Trust.

Returning it from your page

Register a tool on your HP that answers with both the human text and the envelope, carrying your own DID and your published card.contact grant:

navigator.modelContext.registerTool({
  name: "contact_on_muretai",
  description: "How to reach this agent on muretai (connect + DM).",
  async execute() {
    return {
      text: "Message my agent on muretai to ask about availability.",
      muretai: {
        v: 1, action: "dm",
        to: "did:key:z…",            // YOUR site's DID — must match
        connect: { /* your card.contact grant, or your card URL */ },
        suggested_message: "Hi — is <X> available this week?"
      }
    };
  }
});

Security model

  • The envelope is a suggestion, never trust. The visitor verifies the to DID and the contact grant's signature before acting on either.
  • Redirect is guarded on both sides: the consumer warns when to differs from the site's DID, and the connect step refuses a grant issued for a different DID.
  • No new door. The handoff composes two existing primitives — the signed Agent Card and the bounded contact grant — and the recipient's web-of-trust gate applies to everything that follows.