agent: add adapter for Coupang

[alectimison-maker]

Summary

• add a Coupang site adapter for the Korean desktop, mobile, and cart shopping surfaces
• give the agent current guidance for Akamai fetch failures, Korean commerce labels, sponsored/default search ranking, variants, seller-specific fulfillment, and Rocket/Wow conditions
• mirror the adapter in Chrome and Firefox with routing, spoofing-boundary, behavior, and parity tests

Motivation

CONTRIBUTING.md lists Coupang as a high-priority East Asia adapter, but WebBrain currently falls back to generic commerce behavior there. Current official search, product, and cart pages expose several non-obvious traps:

• 바로구매 sits next to 장바구니 담기 but skips the cart
• default 쿠팡 랭킹순 results include sponsored AD items, while shipping-inclusive price comparison requires 배송비 포함 and 낮은가격순
• seller, delivery fee, and arrival date belong to the selected offer, while reviews may be pooled across sellers
• background HTTP requests can receive an Akamai Access Denied response even when the active shopping tab remains usable

Without site guidance, these behaviors can lead to unsafe buy-now clicks, incorrect cheapest-price claims, seller/review conflation, or repeated failed fetches.

Design

The adapter matches only the Korean customer shopping surfaces at the apex, www, m, and cart hosts. It deliberately excludes the Wing seller portal, the separately localized Taiwan storefront, unresearched subdomains, and suffix/path lookalikes.

Six dated, imperative notes tell the agent to:

• fall back to page/DOM tools after an observed Akamai fetch block
• distinguish add-to-cart from buy-now
• use explicit price sorting and shipping-inclusive comparison rather than default/ad position
• select the exact option and compare unit prices
• verify the selected seller's rating, delivery fee, and arrival date independently from pooled product reviews
• treat Rocket/Wow delivery and savings as offer- and membership-conditional

This follows the existing regional-adapter shape without adding APIs, permissions, dependencies, or network calls.

Testing

• production-module focused assertions for trusted/rejected URLs and Chrome/Firefox note parity — passed
• node --check src/chrome/src/agent/adapters.js — passed
• node --check src/firefox/src/agent/adapters.js — passed
• exact Chrome/Firefox Coupang-block diff — passed
• npm run test:security — passed, 60/60 checks
• npm run test:webmcp — passed with real Chrome
• node test/run.js — 1,354 passed; one unchanged baseline failure remains because package.json is 26.0.1 while the newest CHANGELOG.md entry is 26.0.0

Compatibility and risks

This is additive prompt metadata with no public API or configuration changes. The main residual risk is UI drift; the notes are dated 2026-07, use stable visible labels rather than selectors, and prescribe the Akamai fallback only after an actual blocked request.

Scope

Taiwan Coupang localization, seller-side Wing guidance, and unknown checkout/subdomain flows are intentionally deferred until they can be researched independently.

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