[matthewwalsh0]

Explanation

For max-amount quotes where the user can't cover origin gas in native token, RelayStrategy uses a gas station flow: it prices gas in the source token with a smaller probe quote, then re-quotes with the source amount reduced by that cost. The adjusted quote is only accepted if validation passes, otherwise the original max quote is used.

Our gas estimate varies slightly between quotes (e.g. +22 gas out of ~970k), and for multi-item quotes the source-token gas cost is Sentinel's rate × our gas estimate. With nothing reserved beyond the probe's cost, the adjusted quote regularly failed affordability by a handful of raw units. Separately, the adjusted quote was rejected whenever its total gas limit exceeded the phase-1 quote's, even when it was below the probe's.

This change:

• Reserves a buffer on top of the probe's gas cost when reducing the source amount. Configurable via confirmations_pay_extended.gasStationCostBuffer (a multiplier, defaults to 1.0, i.e. no buffer until configured).
• Removes the gas limit checks (shape and total) on the adjusted quote. In the 7702 gas station flow the relayer sets the on-chain gas, and our limit only affects the cost estimate, which the affordability check already validates.

References

• Extracted from feat(transaction-pay-controller): support max quotes in server strategy #11418, which moves this flow into a shared utility used by both the Relay and server strategies.

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Changes max-amount quote math and acceptance rules in RelayStrategy; misconfigured buffer could reduce spendable amount or accept quotes that previously fell back to phase 1.

Overview
Relay max-amount gas station now reserves extra headroom on top of the probe quote’s gas cost when computing the phase-2 source amount, and no longer rejects adjusted quotes based on gas-limit shape or totals between phases.

A new feature flag confirmations_pay_extended.gasStationCostBuffer (multiplier, default 1.0) drives getGasStationCostBuffer(); values below 1 fall back to the default. Phase-2 acceptance still requires source gas-fee-token pricing and the existing affordability check.

Tests and changelog document the new flag and updated fallback vs phase-2 expectations when gas limits or costs drift slightly.

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