cp10 docs — index

Everything documenting the standalone checkout engine in checkout-eet-engine-cp10/cp10-prime-docs/, newest first. cp10 is a research instance — fully built and tested, no production traffic of its own (rollout deferred to the production successor, decision 2026-06-10). It proves a cleaner checkout can be built — groundwork for the OKR of a 20% conversion lift across high-impact last-touch touchpoints (abandoned-cart journey, instant offer, checkout page) — and these docs make it understandable.

Start here New to cp10? Read the guided walkthrough first, then the contract in prime-checkout-eet-engine-cp10.md (the prime — load handshake, isolation boundary, traps). REQ-by-REQ traceability lives in implementation-history.md; the original plan of record is specs/cp10-standalone-checkout-engine.md.

2026-06-10_0113_cp10-how-it-works-walkthrough.htmlEntry point
How cp10 works, as a guided tour: the cast → how the engine is injected same-document into the host page → a card purchase end to end → the two-tier decline mapper → the PayPal express popup flow → the isolation boundary → poke-it-yourself commands and a code reading order. Four live screenshots (engine injected in the page, generic decline banner, PayPal overlay mid-handshake, PayPal decline banner with payer write-back) plus sequence diagrams for each flow.

2026-06-10 01:13self-contained html
2026-06-09_2338_UR-196-cp10-engine-status.htmlDelivery record
Historical status report of the UR-196 build batch: all 17 REQs with commits (scaffold, decline codes, postMessage hardening, version field, unit + e2e tests, hardening follow-ups), the annotated standalone-serve screenshot, the isolation-boundary diagram, limitations, and the rollout design (now deferred to the production successor). Rollout rows are marked Not executed per the 2026-06-10 research-instance scoping.

2026-06-09 23:38self-contained html
decline-codes-investigation.mdInvestigation
The REQ-565 investigation behind the decline-code map: the golden-case table (every legacy banner verbatim), match-order pitfalls (why the substring chain was brittle — the PayPal-400 root cause), the structured-code finding (no decline code reaches the frontend), and the operator live-capture follow-up. Input to REQ-566/569/582.

2026-06-09markdown
2026-06-08_1902_cp10-engine-upgrade-proposal.htmlSuperseded
The original upgrade proposal. Its DRY/shared-module thesis was overruled by the adversarial plan (specs/cp10-standalone-checkout-engine.md — fault isolation via deliberate duplication, zero shared code). Kept for provenance only; do not learn the design from this document.

2026-06-08 19:02html

Ordering is newest-first (LIFO). When adding a doc: drop the dated file (+ optional sibling asset folder) into cp10-prime-docs/, add an entry at the top of this list, and link it from the prime's "cp10-prime-docs (satellite docs)" section. Pattern mirrors cp-eet_9-layout-update/cp9-prime-docs/docs-index.html.