agent: add adapter for Marktplaats

[alectimison-maker]

Summary

• add a Marktplaats.nl site adapter to both browser builds
• distinguish bidding, messaging, and Direct Kopen so the agent does not treat Dutch classifieds like a conventional cart store
• cover strict hostname matching, transaction guidance, spoof rejection, and browser parity

Motivation

Marktplaats is listed as a high-priority regional site in CONTRIBUTING.md. Its listing flow has three materially different paths: a bid may be accepted, rejected, or countered; an accepted eligible bid is paid from Berichten within 72 hours; and Direct Kopen skips negotiation while adding buyer-protection, shipping, and service costs. Without site guidance, an agent can mistake an asking price or accepted bid for a completed purchase and miss the final payable total.

The flow details are based on the current official Marktplaats Help pages for bid/payment requests, Direct Kopen, and shipping.

Design

The adapter uses a strict apex/www.marktplaats.nl matcher and six dated prompt bullets. The notes describe stable transaction states and visible Dutch labels rather than selectors. The exact adapter is mirrored to Chrome and Firefox.

This is site-specific instead of reusing the eBay adapter because Marktplaats bidding is a seller-negotiated classifieds flow, not an auction/cart flow.

Testing

• focused production-module contract check for trusted URLs, spoofed URLs, and Chrome/Firefox parity — passed
• node test/security/injection-corpus.mjs — 60/60 passed
• node test/run.js — the new Marktplaats test passed; the command still exits 1 on the upstream baseline's existing package/changelog mismatch (26.0.1 versus 26.0.0)

Compatibility and risks

This is additive prompt guidance only: no API, config, storage, permission, or format changes. The main residual risk is future UI terminology drift, so the notes are dated 2026-08 and avoid selectors. No live extension trace was recorded in this environment.

Scope

This PR intentionally covers only Marktplaats.nl. Other regional classifieds sites and marktplaats.be are deferred to separate contributions.

[vercel]

@alectimison-maker is attempting to deploy a commit to the esokullu's projects Team on Vercel.

A member of the Team first needs to authorize it.