docs(dev): Rex5 KeylessDeploy gas billing and SequencerRegistry note

[Troublor]

Summary

Addresses the remaining items from the doc-audit (the Rex4 → Rex5 staleness in overview.md was already fixed on main):

• KeylessDeploy (Rex5 gas billing): documents that the outer transaction now pays dispatch overhead + sandbox gas used + signer materialization storage gas, with a billing table, sizing guidance for relayers, and a migration danger hint (10–100× relayer-side budget increase for storage-heavy deploys).
• Documents related Rex5 KeylessDeploy behavior: trailing-bytes rejection, fee-free sandbox (signer needs no gas balance), GASPRICE == 0 inside the constructor, gasLimitOverride capped to the outer call's remaining gas, and sandbox resource usage counting toward the outer transaction's resource limits.
• SequencerRegistry: adds a protocol-facing note under the system contract table with a link to the spec page.
• Adds Rex5 to the spec-name terminology list in docs/AGENTS.md.

Verified against mega-evm origin/main: docs/spec/upgrades/rex5.md (§23 outer EVM gas debit), docs/spec/system-contracts/keyless-deploy.md, docs/spec/system-contracts/sequencer-registry.md, and crates/mega-evm/src/sandbox/execution.rs.

Test plan

• Markdown-only change; verify rendering and links in the GitBook preview.
• Cross-checked all stated gas values and behaviors against the Rex5 spec and implementation.

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This PR was generated by an automated agent.

[github-actions]

The (first attempt) parenthetical is ambiguous — it could be read as "first of several retries" rather than "first time this signer address is ever materialized." Consider dropping it since the "does not exist yet" condition is already self-explanatory, or replace with a cleaner qualifier:

Suggested change

	| Signer materialization | New-account storage gas for the inner signer | Only if the signer account does not exist yet (first attempt) |
	| Signer materialization | New-account storage gas for the inner signer | Only if the signer account does not exist yet (one-time per signer address) |

[Troublor]

Addressed in cc415d9 — replaced "(first attempt)" with "(one-time per signer address)".

[github-actions]

Review

Good PR — well-scoped Rex5 documentation update with accurate spec cross-references. Conventions are followed throughout.

Checklist

• One sentence per line
• GitBook hint blocks correctly opened/closed
• Spec links use absolute https://docs.megaeth.com/spec/... URLs
• Relative link resource-limits.md resolves correctly (file exists in same directory)
• No new pages, so SUMMARY.md update not needed
• Existing frontmatter on system-contracts.md intact

Notes

• The danger hint ordering (Rex5 migration note before the sizing hint) is correct — developers need to know about the budget increase before they read the sizing guidance.
• The "Dispatch overhead — retained even if the deployment is rejected" wording is clear in context: "rejected" refers to a failed sandbox deployment, not a reverted outer call.

One minor clarity suggestion left as an inline comment on the billing table.

[github-actions]

Changes look correct and well-structured. One open inline thread remains unresolved — the (first attempt) parenthetical in the signer materialization row of the gas billing table. Address that before merging.

[github-actions]

Review

LGTM with one minor note. The prior thread on signer materialization wording (PRRT_kwDOODfgX86Iq6Ns) was addressed — the current text uses the suggested (one-time per signer address) form — please resolve it manually.

What looks good:

• Gas billing table is accurate and well-structured; the three-row breakdown (dispatch overhead / sandbox gas / signer materialization) maps cleanly to what the spec describes.
• The sizing guidance paragraph and gasLimitOverride cap note are the right level of detail for a developer doc.
• Migration danger hint is appropriately placed and the 10–100× range is a useful order-of-magnitude signal.
• Precondition additions (trailing-bytes rejection, fee-free sandbox) are concise and correct.
• One sentence per line throughout — formatting is consistent.

One nit:
In the new SequencerRegistry prose paragraph the contract name is styled as _SequencerRegistry_ (italic). Every other contract name in this file is either a link or plain text; a code span (`SequencerRegistry`) would be more consistent with how technical identifiers are rendered elsewhere, but this is a minor preference — not a blocker.

[Troublor]

why is this new SequencerRegistry system contract not put in the table?

[Troublor]

@mega-putin why is this new SequencerRegistry system contract not put in the table?

[mega-putin]

Good catch.
I had called out SequencerRegistry in the intro prose because most dapp code does not interact with it directly, but I agree it should still be in the table since it is a canonical system contract with a fixed address that developers may need to reference.
I’ve added it to the table and kept a short section below for context.

[github-actions]

Both prior thread issues are resolved: SequencerRegistry is in the table, and the "(one-time per signer address)" wording is in place.

The new content is clean:

• Gas billing table is accurate and follows the summarize+link pattern from the dev-layer AGENTS.md.
• Correct hint levels: danger for the Rex5 migration breaking change, warning for the existing gas sizing guidance.
• One-sentence-per-line convention is maintained throughout.
• Spec URLs use the correct absolute form (docs.megaeth.com/spec/ with the system-contracts/ prefix).
• SequencerRegistry section is appropriately minimal given "most dapp code does not call it directly" — no interface needed.
• Rex5 added to the spec-names terminology table in docs/AGENTS.md.

LGTM.

[mega-putin]

Thanks — glad this looks good now.