Fail closed when the wallet screen cannot confirm an approval

[vvillait88]

Summary

Both wallet-OFAC paths branched on if decision == "deny", so everything that was not literally the string "deny" was permitted by structure: None from an unreadable response, and any decision value the API adds later. Both paths already deny on an API outage and describe themselves as strict-liability, so letting an unreadable answer through contradicted their own posture. On the compute-first path it would have settled the payment.

Sites: agentscore_commerce/checkout.py (_run_wallet_sanctions_only) and agentscore_commerce/checkout_compute_first.py.

Both now deny unless the decision is exactly "allow". A missing or null decision is an unreadable response rather than a verdict about the buyer, so it maps to api_error, matching how an outage is already reported on these paths; a decision that is present but not an approval keeps wallet_not_trusted.

Found by the Q3 2026 penetration test, worked with Varun. The node-commerce half is PR #118 there, and the API half has already landed in core.

Type of change

• Bug fix (no breaking change)
• New feature (no breaking change)
• Breaking change (existing callers must update)
• Docs, tests, or internal maintenance only

No exported surface changes. The only behavior difference is that a response which could not be read as an approval is now refused; a merchant relying on that was relying on the defect.

Public API

None. No signature, model or response shape changes.

Behavior changes for two response shapes that should not occur against a current API: an assess response with no decision, and one carrying an unrecognised decision value. Both now deny where they previously allowed, returning api_error and wallet_not_trusted respectively.

Test plan

uv run ruff check, uv run ruff format --check and uv run ty check all clean. uv run pytest: 1868 passed, 4 skipped, coverage 95.37% (above the 95% gate).

Five new tests across the two paths: missing decision, explicit null decision, and an unrecognised decision value, asserting on both the denial code and, for compute-first, that verify_payment was never called so no settle occurred.

Both guards were drilled rather than assumed: restoring the original decision == "deny" check in both files fails 5 of the new tests, and every one passes again once reverted.

Deliberately not added: a policy_result check. Neither path sends a merchant policy, so requiring one would deny every call, since policy_result is correctly null when no policy was submitted. That half of the finding lives in the node gate, which does send policies.

Checklist

• Tests cover the new behavior, and the suite passes locally
• Lint, format, and type checks pass
• Docs and README examples updated if the public surface changed
• No secrets, credentials, or personal data in the diff or the tests