[rgarcia]

Summary

Vault fill rejects a binding whose selector matches more than one element across the page and its iframes, returning ambiguous_selector without writing anything. Hosted card-field iframes such as Shopify checkout's each contain hidden decoy inputs with the same name as the real field. As a result, input[name='number'] fails even though only one input is visible. The manage_vault_items inputs description told agents to target the input inside nested iframes but didn't mention that selectors must be unique, so agents reached for name selectors and the first fill failed.

This adds one sentence to that description: each selector must match exactly one element across frames, and a hidden duplicate is common in payment iframes, so select by an attribute only the visible input has. On Shopify, for example, input[data-current-field='number'] matches only the visible input.

Testing

• Changes only the tool description string. No behavior change, so no new tests.
• bun test: 1139 pass, 0 fail. tsc --noEmit is clean. Prettier check passes on the changed file.
• The selector behavior was observed on a real Shopify checkout: name selectors returned ambiguous_selector, and data-current-field selectors filled all three fields.

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Project	Deployment	Actions	Updated
mcp	Ready	Preview	Nov 9, 2026 6:10pm UTC