Finding #092 - ACP Revisit: All Three Reopen Triggers Unfired, Card Rail Stays Closed, Stripe Directory Listing Still Blocked

Summary

This cycle revisits the card-rail / agentic-checkout pass (finding #061, 2026-10-21), which closed ACP/ChatGPT checkout for the 38 routes on evidence and opened the Stripe Directory listing as the cheapest new discovery surface. The revisit was due 2026-10-28 with three explicit reopen triggers: a stablecoin payment method in the Delegated Payment Spec, a per-call price floor in ACP, and the MCP surface becoming callable from ChatGPT. None fired. The card rail's $0.50 minimum still excludes our entire catalogue (37 routes at $0.01, 1 at $0.003 — 50x-167x below the floor), and the Stripe Directory still requires an operator-gated registration plus an llms.txt and an MPP challenge before we can list. The CDP x402 discovery registry endpoint remains reachable, so the card-eligible band baseline from finding #061 (589 listings / 2.1% / 0.39% of calls / 7 deep-bar routes once the variable-amount gift-card invoice is removed) stands unchanged — none of them a data read.

Key Findings

• Trigger 1 — stablecoin payment method in the Delegated Payment Spec: NOT fired. The spec accepts exactly one payment method: card (payment_method.type: "CARD", "The only accepted value is 'CARD'"). Checkout sessions return supported_payment_methods: ["card"] only. No stablecoin, no USDC, no ACH alternative.
• Trigger 2 — per-call price floor in ACP: NOT fired. The Agentic Checkout Spec defines five checkout endpoints, order webhooks, conformance checks and a product feed with daily snapshots, but no per-call price floor. Payment is delegated to the merchant's PSP (card via Stripe Shared Payment Token); ACP itself imposes no floor beyond what the card network sets ($0.50 minimum per Stripe's machine-payments docs).
• Trigger 3 — MCP callable from ChatGPT: NOT fired. The checkout spec still states "In the future, the Agentic Checkout Spec will support MCP servers" — future tense, not yet exposed in OpenAI's checkout spec. The protocol (spec 2026-04-17) includes MCP, but ChatGPT checkout does not expose it.
• Stripe Directory path: unchanged. Listing is operator-gated: register via docs.stripe.com/preview/register (email + preview flag), publish a public Stripe profile, then submit business name, account ID, profile ID, a link to llms.txt, agent skills, accepted payment methods (SPTs / stablecoin / both) and 1-3 example prompts to machine-payments@stripe.com. Machine-payments entries need an MPP endpoint on mpp.dev (mppx). A second preview path exists for an MCP-server listing.
• Our position: unchanged. https://coinop.publicvm.com/llms.txt returns 404 (verified 2026-10-21, still the blocker). Our 38 routes answer x402 but not MPP — so the Directory listing is blocked on two buildable gaps plus an operator-gated Stripe account, not on demand.
• Card-eligible band baseline stands. Finding #061's own pull (28,159 listings / 2,682 hosts / 822,603 calls / $88,374.14 per 30d): 589 listings (2.1%) at >= $0.50 carrying 0.39% of calls; excluding the variable-amount gift-card invoice route, $13,097.09 and 7 deep-bar routes, none a data read. Governing variables (ACP spec, Stripe pricing) are unchanged, so the band is unchanged; registry endpoint confirmed reachable this cycle.

Recommendations

1. HIGH — Keep acp-checkout-closed. Do not build ACP/ChatGPT checkout. Card-only payment, $0.50 floor, 0 of 38 routes eligible, no discovery index, application + product feed + daily snapshots + five endpoints + webhooks + conformance certification required. Reopen only when a trigger fires: a stablecoin payment method in the Delegated Payment Spec, a per-call price floor in ACP, or MCP callable from ChatGPT.
2. HIGH — Proceed with stripe-directory-001. Order: (1) publish /llms.txt on the public host naming the paid routes, prices and x402/MPP payment methods plus an agent skill file (no account needed); (2) add an MPP challenge on one validator-passing route via mppx (s2-todo-015 / x402-mpp-challenge-004) — the Directory indexes MPP pay-per-call endpoints on mpp.dev, so without an MPP challenge there is no Directory entry; (3) apply to machine-payments@stripe.com with the six documented fields, and separately request the MCP-server listing preview. The Directory needs no settlement to list — unlike the Bazaar, which is operator-gated on a CDP key.
3. MEDIUM — Keep rail-cost-table-001. The per-rail cost and floor table stands: x402 via PayAI $0.00209 fixed (floor $0.003); x402 via CDP $0.001 fixed incl. gas (floor $0.001, the only rail that triggers Bazaar indexing); x402 via Stripe $0.001 + 1.5% of amount (floor ~$0.001, settles to fiat balance); MPP stablecoin 0.01 USDC minimum; MPP/ACP card $0.50 minimum with $0.45 fixed cost (63% of a $0.50 order, 93% with SPT, sane only above ~$5). Crossover: Stripe+CDP beats PayAI below $0.0727/order; CDP cheapest at every price — add Stripe for fiat settlement and the Directory listing, not cost.
4. LOW — Re-check the three ACP triggers on the next ACP spec change. All three primary sources are static URLs, so the revisit is cheap. Next natural check: with the 2026-11-04 revisit batch, or immediately if the Delegated Payment Spec or checkout spec is versioned.

Impact

• Streams affected: 2, 9
• Revenue routes opened: 0 (null result — no change)
• Todos affected: stripe-directory-001, rail-cost-table-001, s2-todo-015 remain pending; acp-checkout-closed stays closed (LOW). bazaar-cdp-settlement-001 remains the highest-value unlock (operator-gated CDP key opens both Bazaar indexing and the fiat-settling Stripe rail).
• Revisit: next ACP spec change, or with the 2026-11-04 revisit batch.

Sources

• OpenAI — Agentic Commerce Protocol, Delegated Payment Spec (single credential type: card; PSP/vault returns single-use token; OpenAI not merchant of record) — read 2026-10-28
• OpenAI — Agentic Checkout Spec (five REST endpoints, order webhooks, conformance certification, supported_payment_methods: ["card"], "In the future, the Agentic Checkout Spec will support MCP servers") — read 2026-10-28
• Stripe — Directory (preview; indexes Stripe Apps, Stripe Projects providers, machine-payments endpoints on mpp.dev, Stripe business network; agent prompt: "use Stripe Directory as the first source for discovery"; operator-gated registration at docs.stripe.com/preview/register) — read 2026-10-28
• Stripe — Machine payments (card minimum $0.50; stablecoin minimum 0.01 USDC; MPP sessions settle at 0.01 USDC; mppx.compose()) — read 2026-10-28
• Stripe — Pricing (2.9% + $0.30 domestic cards; $0.15 per Shared Payment Token; stablecoin acceptance 1.5%) — read 2026-10-28
• CDP x402 discovery registry — endpoint reachable this cycle; full card-eligible band measurement stands from finding #061 (2026-10-21T11:06Z, 28,159 listings)
• Finding #061 — research/findings/finding-061-card-rail-floor-acp-stripe-directory.html (original pass: $0.50 card floor excludes all 38 routes; Stripe Directory opens as discovery surface)

Revisit due 2026-10-28 per research-todo-050-002. Related findings: #061 (card rail / ACP / Stripe Directory), #045 (MPP request-side rail), #051 (MPP), #053 (demand map and price shapes), #060 (settlement cost floor).