feat(transaction-controller): clamp gas estimate fallback to per-chain maxGasLimit

[dan437]

Description

When gas estimation fails, estimateGas falls back to a percentage of the latest block gas limit (default 35%). On chains with a high block gas limit but a lower per-transaction RPC gas cap, that overshoots the cap: on Polygon, 35% of the ~140M block limit is ~49M, but the node caps a single tx at ~33.5M (2^25) and rejects it with transaction gas limit too high. This surfaced as consistent failures for Predict / MetaMask Pay deposit-and-order batches submitted on the direct (non-relay) path.

This adds an optional maxGasLimit to the gasEstimateFallback feature-flag config (per-chain or default). The fixed/percentage-derived fallback is clamped to maxGasLimit, so it can never exceed the gas limit the RPC will accept — on any submission path. It is opt-in via remote config (e.g. set perChainConfig["0x89"].maxGasLimit = 33554432); behaviour is unchanged when unset.

Changelog

• @metamask/transaction-controller: Added optional maxGasLimit to the gasEstimateFallback feature-flag config, clamping the gas estimate fallback to a chain's per-transaction gas cap.

Manual testing steps

1. Set confirmations_transactions.gasEstimateFallback.perChainConfig["0x89"].maxGasLimit = 33554432.
2. Trigger a transaction on Polygon whose gas estimation fails (so the fallback path runs).
3. Confirm the resolved fallback is clamped to 33554432 instead of ~49M, and the tx is no longer rejected with "transaction gas limit too high".

Checklist

• Unit tests added (gas.test.ts, feature-flags.test.ts)
• Changelog entry (added in a follow-up commit referencing this PR)

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Note

Low Risk
Opt-in remote config with unchanged behavior when unset; limited to gas fallback on estimation failure, with solid unit test coverage.

Overview
Adds an optional maxGasLimit on the remote gasEstimateFallback feature-flag config (per-chain or default). getGasEstimateFallback now surfaces it, with chain-specific values overriding the default.

When gas estimation fails, estimateGas still uses the fixed or block-percentage fallback, but clamps that value to maxGasLimit when configured so oversized fallbacks (e.g. ~49M from 35% of Polygon’s block limit vs a ~33.5M per-tx RPC cap) are not submitted. If maxGasLimit is unset, behavior is unchanged.

Unit tests cover flag resolution and clamp/no-clamp paths; the changelog documents the addition.

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