fix(transaction-controller): use node-authoritative gas estimation

[pedronfigueiredo]

Explanation

Transaction Controller currently skips eth_estimateGas for ordinary no-data transfers to recipients without code and assigns a fixed 21,000 gas limit. That assumption is not valid across transaction shapes and active fork rules, including EIP-2780 networks, and cannot account for node state such as account creation or delegation resolution.

This change removes the fixed-gas shortcut so transactions without caller-provided gas use the selected network client's existing node/simulation estimation path. Caller-provided gas remains authoritative, and existing percentage/fixed-feature fallbacks plus simulationFails reporting are preserved when estimation fails.

Specifically, this changes gas-limit estimation, not gas-price estimation. For an ordinary transaction without caller-provided gas, Transaction Controller calls eth_estimateGas on the node selected by networkClientId and may apply the existing gas buffer. gasPrice, maxFeePerGas, and maxPriorityFeePerGas continue to come from the existing gas-fee estimation flows; the eventual transaction fee combines those prices with the node-estimated gas limit.

The focused test matrix covers legacy and upgraded node responses for self-transfers, zero-value transfers, existing and new recipients, contract creation, and delegated sender/recipient cases. It also verifies complete transaction-shape forwarding and estimation failure behavior. Existing type-4 composition remains unchanged because it is owned by CONF-1997.

Validation

• yarn workspace @metamask/transaction-controller run test
• yarn build
• yarn workspace @metamask/transaction-controller run build
• Targeted ESLint and Oxfmt checks
• yarn workspace @metamask/transaction-controller run changelog:validate

References

• CONF-1995
• EIP-2780
• Follow-up ownership: CONF-1997 (type-4 composition)
• Cross-client validation: CONF-2003

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 default gas limits for many wallet-initiated sends, which affects fees and inclusion; wrong estimates could cause reverts, though fallbacks and explicit gas remain.

Overview
Gas limit estimation no longer short-circuits plain no-data transfers to empty recipients with a hard-coded 0x5208 (21,000) limit. The removed requiresFixedGas / eth_getCode path and FIXED_GAS export are gone; when the caller does not set gas, updateGas always goes through estimateGas on the networkClientId client (simulation when enabled, otherwise eth_estimateGas), with existing buffers and failure fallbacks unchanged.

Caller-provided gas is still used as-is. Gas price flows are untouched. Tests and integration mocks now expect eth_estimateGas for simple sends and cover varied shapes (self-transfer, new accounts, contract creation, EIP-7702 delegation). The changelog documents the behavior change.

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