Add August 2026 changelog

[jlin27]

Summary

Adds fern/docs/changelog/2026-08-31.mdx, covering changes merged between 2026-08-01 and 2026-08-31.

Headline items:

• New liquidity sources on Base (Forte), BSC (Lista V3), HyperEVM (BrownFi V3, Funnel, HyperTrade, Turbo, Upheaval V3), Polygon (QuickSwap V4) and Robinhood Chain (Alandale, Alandale CL, BrownFi V3, Curve, ERC-4626 vaults, Parity V3).
• New features: the collectedBy field on Cross-Chain fee entries, and erc7597Permit as a Gasless approval.type.
• Bug fixes: fee-on-transfer buyTaxBps/sellTaxBps returning 0, Relay-collected integrator fee undercollection, 400 instead of 500 on invalid /cross-chain/quotes input, and stale failure blocks on /cross-chain/status.
• Breaking changes: Across V4 no longer serves Solana or HyperCore; Monad is no longer a Mayan origin.

Every backticked identifier, endpoint path and enum value in the entry was checked against fern/openapi.json or fern/openapi-cross-chain.json before being written.

Stale docs fixed

No page edits in this PR — the two pages that need updating are both already open in #280.

• Across V4 / Solana and HyperCore — fix: Update supported chains by Across #280 already flips these cells in introduction/supported-chains.mdx and updates cross-chain-api/guides/cross-chain-swaps-to-hypercore.mdx. Not duplicated here.
• Mayan / Monad — still stale, not fixed here. In introduction/supported-chains.mdx the Cross-Chain matrix marks the Monad row as ✅ for Mayan Swift, Mayan MCTP and Mayan FastMCTP. Monad was dropped as an origin for all three this month and kept as a destination, so those three cells should read dst. Left out deliberately: fix: Update supported chains by Across #280 is already editing adjacent rows of the same table, and the guidance for this changelog is to leave overlapping files alone rather than race them. Worth landing as a follow-up once fix: Update supported chains by Across #280 merges.

Notes for review

• The published OpenAPI specs in this repo were last synced from source on 2026-08-07 (2ec0a99). Everything verifiable in the spec therefore comes from the first week of the month; API-surface changes merged between 2026-08-08 and 2026-08-31 could not be confirmed against a published spec and were left out. A spec sync would let a follow-up pass pick those up — worth checking before the September entry.
• Several changes in this window add request parameters or response fields that have no presence in the published specs and look like they were meant to be public, including token-metadata fields and two simulation request options. They are omitted here under the verify-before-documenting rule, and are the most likely candidates to surface once the specs are re-synced.
• Judgment call on the Across V4 entry: it names Solana alongside HyperCore. Solana-only changes are normally out of scope for these changelogs, but this removal is not Solana-only, and describing only half of a breaking change seemed worse than the scope convention. Happy to trim it to HyperCore if you'd rather hold the line.
• A number of changes this month expanded how existing liquidity is discovered rather than adding anything new to route against, and several others only altered internally stored or internally configured state. Both classes were dropped rather than reworded — no integrator can observe them. Sources already announced in earlier months were also excluded, on a cross-check against the last three entries.
• The internal process doc for this changelog is present in the source checkout and matches the current policy; no divergence to report.

[github-actions]

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• changelog/2026/8/31