Plan: agent-delegable payment-provider connect (without making it a fund-redirection key)

Status: APPROVED — agreed shape, ready to build. No urgency (doc-harness Path 1, no payments, ships first; this work feeds Path 2, the full regtest buyer-pays walkthrough). Author: this session, 2026-06-16. Sign-off: other dev, 2026-06-16. Related: merchant-onboard role shipped in 0.2.0:57 (src/api/api_keys.rs); multi-provider model (plans/multi-provider-payment-model.md).

1. Problem / motivation

Make Keysat fully agent-compatible: an operator hands an agent a scoped credential and says "add Keysat licensing to this software and connect a Bitcoin wallet on BTCPay," and the agent does the whole thing over the API. Two use cases:

Production delegation — a real operator delegates first-time setup (catalog + connect their BTCPay) to an agent.
Doc-onboarding test harness — a fresh AI agent integrates Keysat from the docs alone against a disposable server, published as marketing ("all the agent had to do was X, Y, Z"). For dev/testing the agent uses regtest (private Bitcoin network — mine blocks on demand, no faucets, no real money).

merchant-onboard (shipped :57) covers catalog + manual license issuance end-to-end but cannot connect a payment provider — that stays master-key only. So the agent story stops one step short of "accept buyer payments."

2. The core risk (why connect is the crown jewel) — ratified

Creating products/policies/licenses is "what you sell." Connecting — or re-connecting — a payment provider is "where the money goes": a credential that can do it can repoint settlement at an attacker-controlled wallet/store, after which every buyer payment lands there. Direct theft-of-funds, strictly worse than any catalog write. The value of a scoped key is bounded blast radius; folding connect into merchant-onboard would make it "near-total financial control with a friendly name."

Binding decision (both devs): do NOT fold connect into merchant-onboard. A key that can repoint settlement is a fund-redirection key; bounding that blast radius is the whole point.

3. Current state (verified against code, 2026-06-16)

All provider-mutating endpoints are master-key only (require_admin):
- BTCPay connect — api/btcpay_authorize.rs:87 (OAuth-style: returns an authorize_url; a human approves on BTCPay, then the callback persists store id / API key / webhook secret).
- BTCPay disconnect — btcpay_authorize.rs:426.
- Zaprite connect — api/zaprite_authorize.rs:56 (API-key paste; no OAuth step).
- Zaprite disconnect — zaprite_authorize.rs:207.
Only payment_providers:read exists as a scope; there is no payment_providers:write today. merchant-onboard grants all :read + products:write + policies:write + licenses:write. Master-only ops sit behind require_admin, never consulting Role::grants.
Asymmetry: BTCPay is self-hosted, can run regtest/testnet (the safe case). Zaprite is a hosted mainnet SaaS — no regtest equivalent assumed, so scoped Zaprite-connect stays master-only and the demo uses BTCPay (the motivating case anyway).

4. Options (B rejected; built shape is C + D, gated by E)

#	Option	Verdict
A	Keep connect master-only (status quo)	Safe, not fully agent-compatible
B	Fold connect into `merchant-onboard`	Rejected (binding) — fund-redirection key
C	À-la-carte scope `payment_providers:write`, never in any default role	Chosen packaging
D	Network gate: scoped connect only regtest/testnet/signet; mainnet → master	Chosen (inner defense)
E	Sandbox-mode daemon flag for disposable instances	Chosen as the OUTER gate (see §5)

5. Agreed design — gate order matters

A scoped payment_providers:write connect is permitted iff ALL hold, checked in this order:

OUTER — sandbox-mode daemon flag is ON. On a production (non-sandbox) daemon, scoped payment-connect is disabled entirely — even regtest. (Refinement, dev: a scoped key connecting a regtest provider on a production box would knock out the live store's real payments — denial-of-revenue, not theft, but still bad. So the flag, not the network, is the first gate.)
INNER — target network is non-mainnet (regtest/testnet/signet). Defense-in-depth so that even on a sandbox daemon a scoped key can't wire up mainnet. Fail closed: if the network can't be positively determined as non-mainnet, treat it as mainnet → deny.
BTCPay OAuth human-approve still happens (someone approves on BTCPay's side).

Master key bypasses 1–2 and may connect any network (still subject to BTCPay's own OAuth).

The sandbox flag is daemon-level config (env / launch), read at boot — NEVER settable via any API, scoped or otherwise. (Refinement, dev: otherwise a scoped key flips sandbox on, then connects. Keep it strictly out-of-band.)

Net: full agent-compatibility for dev/testing on a sandbox+regtest instance (zero master-key steps — the doc-harness Path 2), and production stays locked: no scoped key can connect, reconnect, or disconnect a provider on a live box.

6. Resolved decisions (the dev's open-question answers)

BTCPay network detection — VERIFIED. Greenfield's GET /api/v1/server/info (ServerInfoData) has no network/chainType field (only syncStatus[].chainHeight etc.). Determine the network from a network-encoding artifact, not a field:
- Primary: fetch a store on-chain receive address — GET /api/v1/stores/{storeId}/payment-methods/{pmid}/wallet/address → OnChainWalletAddressData.address — and classify by prefix: bech32 HRP bc1…=mainnet, tb1…=testnet/signet, bcrt1…=regtest (legacy base58 1/3=mainnet vs m/n/2= test/regtest).
- Secondary: the on-chain payment method's derivationScheme (NBXplorer format) — xpub/ ypub/zpub=mainnet, tpub/upub/vpub=testnet. (Fetching config needs btcpay.store.canmodifystoresettings.)
- Fail closed: Lightning-only store / no address / unrecognized prefix → treat as mainnet → require master.
Zaprite — no non-mainnet mode assumed → scoped Zaprite-connect stays master-only; demo uses BTCPay. (Agreed.)
Reconnect / rotate of an already-connected mainnet provider — always master-only. (Strong yes — that's the exact attack.) Sandbox/regtest reconnect follows the §5 scoped rules; mainnet reconnect is never scoped.
Packaging — à-la-carte payment_providers:write (composes with merchant-onboard, avoids role sprawl), not a new fixed role. Implementation note: "composes with" means moving from one-role-per-key to role + optional extra scopes per key (or full per-key scope sets) — a schema addition (scoped_api_keys gains a scopes column, migration 0024). Acceptable given no urgency; flagged so it's not a surprise at build time.

7. Design sketch (build)

Scope string: add "payment_providers:write". Granted per-key (à-la-carte, §6.4), never via a :write suffix match, never in merchant-onboard's grant set.
Sandbox flag: e.g. KEYSAT_SANDBOX_MODE=1, read at boot into AppState; surfaced read-only in /v1/admin/tier-style status + a prominent "SANDBOX" banner in the admin UI so a sandbox instance is never mistaken for production. No setter endpoint of any kind.
Gate helper: replace require_admin on the connect handlers with require_provider_connect(state, headers, target_network):
- master → allow any network;
- scoped w/ payment_providers:write → allow iff state.sandbox_mode and target_network != mainnet;
- else 403. Resolve target_network (§6.1) before persisting anything.
Reconnect/disconnect: mainnet reconnect always master-only (§6.3); disconnect on a production daemon stays master-only (denial-of-revenue, consistent with §5.1). In sandbox, both follow the scoped rule.
Audit: every scoped connect writes an audit row with actor hash + resolved network + provider.

8. Migration / back-compat

New scope string + gate helper + sandbox flag. Migration 0024 only for §6.4 (per-key extra scopes column on scoped_api_keys).
Master-key automation unaffected; existing merchant-onboard keys unaffected (capability unchanged); existing keys default to no extra scopes.

9. Testing

Scoped payment_providers:write key on a sandbox daemon: connect regtest BTCPay → allowed; connect mainnet BTCPay → 403; Lightning-only / unknown network → 403 (fail-closed).
Same key on a production (non-sandbox) daemon: connect regtest → 403 (outer gate); proves §5.1.
Sandbox flag is not flippable via API (assert no endpoint mutates it).
Master key: connect any network → allowed.
merchant-onboard without the extra scope → 403 on connect everywhere (proves no role widen).
Mainnet reconnect/rotate → master-only even in sandbox.

10. Status

Shape approved by both devs: C (à-la-carte payment_providers:write) + D (network gate, fail-closed) gated by E (sandbox flag as the outer gate, daemon-level only), BTCPay OAuth preserved, B explicitly rejected. Build when it suits — Path 1 ships first.

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