docs: reconcile SSTORE gas to 72,000 (same on both networks, Prop #109)

[alexander-sei]

Problem

The docs contradicted themselves on the SSTORE (storage write) gas cost, which confuses developers and any AI assistant trained on the docs:

• skill.md — "72,000 on both mainnet and testnet"
• ai/sei-skill/index.mdx — "72,000 on testnet, 20,000 on mainnet"
• ai/sei-skill/prompts.mdx — example prompt implying testnet > mainnet

These can't all be right.

Resolution

SSTORE is 72,000 gas — the same on pacific-1 and atlantic-2 (it does not vary by network), governance-adjustable.

Verified empirically. I measured the marginal cost of a cold (zero→nonzero) storage write via eth_estimateGas against both live EVM RPCs (contract-creation bytecode doing 0/1/2/3 fresh writes). Both networks returned byte-for-byte identical estimates; the per-write marginal is ~74,100 = 72,000 base + 2,100 EIP-2929 cold-access + minor overhead. (Standard Ethereum would be ~22,100.)

Source of the value: mainnet governance Proposal #109 "Update EVM SSTORE set gas to 72000" (PASSED), which set the evm module param KeySeiSstoreSetGasEIP2200 = "72000". (The previously-cited "#240" was incorrect — it doesn't exist on mainnet, and on testnet it's a v6.3.0 upgrade.)

Changes

• skill.md, ai/sei-skill/index.mdx, ai/sei-skill/prompts.mdx — state 72,000, same on both networks, governance-adjustable; cite Prop #109; the example prompt no longer implies a false testnet-vs-mainnet difference.
• evm/differences-with-ethereum.mdx (canonical reference) — notes same-on-both + Prop #109, and warns that a forge test --gas-report --fork-url report forks state but applies revm's standard EVM schedule (~22,100), so it understates Sei's cost — use live eth_estimateGas.
• evm/evm-parity/gas-and-fees.mdx — adds the current value, links the canonical page, and adds the same fork-report caveat.

All SSTORE statements across the affected docs now agree and point to the canonical reference.

Scope note

This PR contains only the SSTORE reconciliation in already-tracked docs. It intentionally excludes the in-progress Agent Skills registry work (.mintlify/skills/, ai/skills.mdx, evm/templates.mdx, snippets/skills-registry.jsx, and the related .gitignore/docs.json changes), which will ship separately.

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Documentation-only changes with no runtime, auth, or deployment impact.

Overview
Aligns SSTORE documentation so everything states 72,000 gas on both mainnet and testnet, governance-adjustable, instead of the old split (e.g. 72k testnet vs 20k mainnet in sei-skill).

sei-skill / skill.md: The comparison table and critical-facts list now match that single value, link to the canonical EVM differences page, and cite governance Proposal #109 (KeySeiSstoreSetGasEIP2200) instead of the incorrect #240 reference. The example prompt in prompts.mdx no longer implies a false testnet-vs-mainnet difference.

Canonical EVM docs: evm/differences-with-ethereum.mdx adds same-on-both-networks wording, Prop #109, and guidance to use live eth_estimateGas on a Sei RPC. evm/evm-parity/gas-and-fees.mdx states the current 72k figure, cross-links the canonical section, and adds a Warning that Foundry forge test --gas-report --fork-url forks state but uses revm’s Ethereum gas schedule (~22,100 for SSTORE), so it understates Sei’s cost.

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