[hiroTamada]

Important

Blocked on the kernel-go-sdk v0.133.0 release. go.mod pins the unreleased release-PR head as a pseudo-version (v0.132.1-0.20261027142730-6b2ae5c1cb1d, commit 6b2ae5c on kernel/kernel-go-sdk#213). Before merging, bump to the published v0.133.0 (go get github.com/kernel/kernel-go-sdk@v0.133.0 && go mod tidy) and re-run the tests.

Summary

The API now supports multiple cards per Kernel wallet (add_payment_method / remove_payment_method) and payment_request items for Link and Kernel purchases. Both are enabled per organization. This PR adds both to the vault commands. Organizations without them keep the original single-card Kernel wallet contract: wallets create --provider kernel still shows the default card's card_enrollment action, and Kernel cards without payment_method_id send the same request as before.

Payment methods

• items invoke <vault> <wallet> add_payment_method and the shortcut wallets add-payment-method <vault> <wallet> print the new method, its status, its card_enrollment URL and expiry, and the existing guidance to share it privately with the cardholder. --open is allowed for a cardholder on their own machine.
• items invoke <vault> <wallet> remove_payment_method --params '{"payment_method_id":"<id>"}' (or --spec-file) and wallets remove-payment-method --payment-method-id <id>, which asks for confirmation unless --yes is passed, print the removal result. They also state that removal is not proof that a payment did not occur.
• Operation results were previously rejected as "unexpected vault operation response"; they now go through their own display-safe projection.
• Errors now come with specific guidance: 409 purchase_unresolved (reconcile the funded purchase first), 409 provider_revocation_pending (method stays removal_pending; retry later), 409 on add (10-method / 3-open-link limits), 403 insufficient_scope (needs vaults:write in addition to vaults:use), and 429 (honors Retry-After). When either operation is not advertised, the error explains when the API offers it.
• wallets payment-methods adds a status column and prints status_reason and any pending enrollment URL with its expiry. The Kernel guidance now covers optional payment_method_id, the default card card, method statuses, and when to remove a method or contact support.

payment_request items

• cards create|update --type payment_request sends type: payment_request through the SDK's PaymentRequest upsert/update params; --type defaults to card. AgentCard is rejected with --type payment_request, and Kernel updates stay blocked as for Kernel cards.
• payment_request items are rendered like card items in items get/list and invoke results, including Link authorize --browser-id/--page-url and fill handling.
• Kernel purchases show payment method id (bound method from state, falling back to spec) and funding status. They warn when funding_status is unavailable or removed.

Output projection

• Payment methods: status, status_reason, expires_at, action.{name,url}. capture_token is never printed in either output mode.
• Item state: payment_method_id, funding_status.
• Event data: item_type, provider, payment_method_id_present (payment_method_id was already kept).

Help

• The Kernel wallet spec, wallet-create text, KernelCardSpec (optional payment_method_id), the payment_request section, items invoke, and the root payment flow now describe empty wallets, add/remove, method statuses, funding_status and the vaults:write requirement.
• reconnect_required guidance now matches the API: legacy wallets refuse payment and deletion until upgraded. The previous "share the new card_enrollment action" no longer applies.

Testing

• make test (go vet ./... + go test ./...): passes.
• golangci-lint run --new-from-rev=HEAD ./... (v2.15.0): 0 new issues. Existing repo-wide warnings are unchanged.
• New and updated unit tests cover add/remove through both invoke and the wallet shortcuts, request bodies, JSON/human projection (including that capture_token is withheld), error guidance per code, the unadvertised-operation message, parameter validation, --open, payment_request create/update/authorize bodies, funding display, event projection, and help text.
• Checked human output manually against a local fake API. Not tested against a live API with the flags enabled.