docs: Task #8 probe results + handoff + PRD AC updates

- Add Handoff - RN Multichain Probe - 2026-05-28.md
- Update Handoff - Request Network In-House Checkout with Task #8 status
- Update Activity Log with backend@ae17b18, frontend@0ebb2f1
- Update PRD §2 acceptance criteria for Task #8
- Update Payment API.md with /api/admin/rn/networks endpoints

08 - Operations/Handoff - Request Network In-House Checkout - 2026-05-28.md

@@ -63,8 +63,8 @@ Five follow-ups scoped for kimi to pick up independently. Full spec in `PRD - Wa
 
 | # | Task                                                          | Priority | Status |
 |---|---------------------------------------------------------------|----------|--------|
-| 7 | Per-(buyer, sellerOffer) ephemeral RN destination wallets     | high     | 🟡 In progress — backend + admin UI shipped in 2.6.42, cart-aware buyer UX + tests + live RN-accepts-divergent-destination probe remain |
-| 8 | Multichain RN proxy registry + USDC/USDT support              | high     | ⏳ Not started |
+| 7 | Per-(buyer, sellerOffer) ephemeral RN destination wallets     | high     | 🟡 In progress — backend + admin UI + cart-aware UX + tests shipped in 2.6.45/2.6.46; **live RN-accepts-divergent-destination probe remains manual** |
+| 8 | Multichain RN proxy registry + USDC/USDT support              | high     | 🟡 In progress — backend registry + probe script + frontend admin page + USDT-mainnet reset shipped in 2.6.46; **BSC USDT paid probe + Base proxy address hunt remain** |
 | 9 | Per-chain confirmation thresholds + admin UI                  | medium   | ⏳ Not started |
 | 10 | Optional AML screening on incoming payments (seller-paid)    | medium   | ⏳ Not started |
 | 11 | Trezor signing for admin actions (release/refund/sweep)      | high     | ⏳ Not started |
@@ -107,7 +107,23 @@ Five follow-ups scoped for kimi to pick up independently. Full spec in `PRD - Wa
 | E — `recordSweep` accumulation fix | ✅ | `$inc: { totalSwept }` instead of `$setOnInsert` |
 | F — API docs | ✅ | Derived-destination endpoints added to `Payment API.md` |
 | B — Unit tests | ✅ | 46 tests across 3 files (see below) |
-| C — Live divergent-destination probe | 🔄 | Protocol prepared; requires manual execution on dev (see §Live multi-seller probe below) |
+| C — Live divergent-destination probe | 🔄 | Protocol prepared; **requires manual browser + wallet execution** (see §Live multi-seller probe below). Dev is running 2.6.46 with all backend/frontend code deployed. |
+
+## Task #8 — completion status
+
+| Item | Status | Notes |
+|------|--------|-------|
+| Probe script | ✅ | `scripts/probe-rn-chains.ts` — 4/5 chains verified (BSC, Arbitrum, Ethereum, Polygon). Base proxy not deployed at canonical address. |
+| Token registry JSON | ✅ | `tokens.json` — USDC + USDT on 4 verified chains with correct decimals |
+| Chain registry JSON | ✅ | `supportedChains.json` — 4 verified chains + Base in `_unverified` |
+| Admin route | ✅ | `GET /api/admin/rn/networks`, `POST /api/admin/rn/networks/reload` |
+| Frontend admin page | ✅ | `/dashboard/admin/networks` renders registry with reload button |
+| `unsupported_chain` reason | ✅ | `buildInHouseCheckoutBlock` returns `unsupported_chain:<id>` |
+| Frontend wagmi multichain | ✅ | Added arbitrum + base to wagmi config with RPC transports |
+| Per-chain explorers | ✅ | Checkout view uses correct explorer per chainId |
+| USDT-mainnet approve reset | ✅ | **Implemented but unverified** — see note in [[Handoff - RN Multichain Probe - 2026-05-28]] |
+| BSC USDT paid probe | 🔄 | **Pending manual execution** — needs real wallet + test BSC USDT |
+| Base proxy hunt | 🔄 | Canonical address has no code on Base. Need RN official docs for actual address. |
 
 ### B — Unit tests (backend@34f542e, 2.6.45)