docs: ship in-house RN checkout, scope 5 follow-up tasks (#7-11)

In-house Request Network checkout went fully end-to-end on dev today.
A real 0.01 USDC payment flowed through wallet connect -> approve ->
ERC20FeeProxy.transferFromWithReferenceAndFee -> RN webhook ->
TransactionSafetyProvider -> Payment.status=completed -> page success
state. Tx 0x494c77a29161b5100d8e0b1ac675f1822955d0bb3633ecdbfafb886f84f2f320.

Docs:
- New PRD: Wallet, Multichain, Confirmations, AML, Trezor
  (5 follow-ups, each sized for an independent contributor)
- Updated PRD: Request Network In-House Checkout (phases 0..3 done,
  phase 4 partial, phases 5-6 not started)
- Updated handoff: deployed versions, what is working end-to-end,
  follow-up tasks index

Taskmaster: 5 new top-level tasks (#7..#11) covering ephemeral
destination wallets, multichain proxy registry + USDC/USDT, runtime
confirmation thresholds, optional seller-paid AML screening, and
Trezor signing for admin actions. Tasks are scoped fine-grained so
each is independent enough for kimi to pick up.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Taskmaster/Tasks/task-8.md

@@ -0,0 +1,35 @@
+---
+taskmaster_id: "8"
+status: "pending"
+priority: "high"
+depends_on: []
+parent_id: ""
+source: "taskmaster"
+generated_at: "2026-05-28T11:49:27.076Z"
+---
+
+# 8 - Multichain RN proxy registry + USDC/USDT support
+
+- [ ] 8 - Multichain RN proxy registry + USDC/USDT support #taskmaster #priority/high #status/pending ⏫ 🆔 tm-8
+
+## Metadata
+
+| Field | Value |
+| --- | --- |
+| Taskmaster ID | 8 |
+| Status | pending |
+| Priority | high |
+| Dependencies | None |
+| Parent | None |
+
+## Description
+
+Probe and persist RN ERC20FeeProxy addresses on BSC/Arb/ETH/Polygon/Base, add USDC + USDT token entries with correct decimals per chain, and surface an admin networks page. Include the USDT-mainnet approve(0) reset quirk in the frontend approve step.
+
+## Details
+
+See PRD - Wallet, Multichain, Confirmations, AML, Trezor.md §2. Tasks: new backend/scripts/probe-rn-chains.ts that walks each chain in supported-chains.json and verifies the canonical 0x0DfbEe143b42B41eFC5A6F87bFD1fFC78c2f0aC9 proxy is the real RN proxy via a known view fn (CREATE2 is deterministic, but verify); promote backend/src/services/payment/requestNetwork/tokens.ts to load from JSON + admin override; add USDT entries on all 5 chains (BSC USDT 18-dec quirk, mainnet/Arb/Polygon/Base USDT 6-dec); buildInHouseCheckoutBlock returns reason='unsupported_chain:<id>' for unknowns; new admin route GET /api/admin/rn/networks + frontend page /dashboard/admin/networks rendering the registry with per-row 'probe again'. Frontend approve flow: if buyer is on Ethereum mainnet AND token is USDT AND current allowance > 0, do approve(spender, 0) first then approve(spender, amount). Acceptance: probe succeeds on at least BSC/Arb/Polygon/ETH/Base; one paid probe on BSC USDT end-to-end; mainnet USDT approve(0) reset works; admin page reflects registry. Dependencies: none — runs in parallel with #9. This is task #8 in the PRD.
+
+## Verification
+
+_No verification strategy._