fix(sdk): accept null for optional fields in swapApprovalResponseSchema

[droplet-rl]

Summary

• swapApprovalResponseSchema rejects valid /swap/approval responses on every bridgeable-to-bridgeable route — Zod's .optional() accepts undefined but not null, and the API now serializes approvalTxns, steps.originSwap, steps.destinationSwap, and swapTx as explicit null when they don't apply.
• Switch the four affected fields to .nullish(). Consumers (executeSwapQuote) already coerce via truthiness, so runtime behavior is unchanged.

Context

Reported by Fun (Connor McEwen) in #fun on 2026-06-10. getSwapQuote throws Invalid swap approval response. Error: ... on quotes like Arbitrum USDC → Optimism USDC (no swap legs). Verified against live app.across.to/api/swap/approval:

crossSwapType: bridgeableToBridgeable
approvalTxns: null
steps.originSwap: null
steps.destinationSwap: null

Root cause on the server side: across-protocol/quote-api#2645 ("epic: hyperliquid withdrawals") flipped these fields from undefined to null in api/swap/_utils.ts:buildBaseSwapResponseJson. A surgical revert of those four lines is being pursued in quote-api; this SDK patch is the integrator-side defense so future server changes that null vs. omit don't break clients again.

Test plan

• pnpm build (tsc) — clean
• pnpm lint — only pre-existing warning unrelated to this change
• Schema sanity-check against Connor's exact payload (null for the four fields) — swapApprovalResponseSchema.safeParse returns success: true
• Reviewer to confirm consumer code paths (executeSwapQuote) still treat null the same as undefined (they do — if (!swapQuote.swapTx) and if (swapQuote.approvalTxns && ...))

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 21c3029

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@across-protocol/app-sdk	Patch

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Project	Deployment	Actions	Updated (UTC)
toolkit-example	Ready	Preview, Comment	Jun 10, 2026 5:06am

[pxrl]

Remember to bump the patch version of the package.

[droplet-rl]

Bumped @across-protocol/app-sdk from 0.6.0 → 0.6.1 in packages/sdk/package.json and committed. The changeset (patch) is already in place.

[dohaki]

@droplet-rl no need to bump the package version. it will be bumped by the changeset PR. also fix the failing test. Scroll is not supported by us anymore

[droplet-rl]

Done. Reverted the version bump (will let the changeset PR handle it) and dropped Scroll from MAINNET_SUPPORTED_CHAINS in packages/sdk/test/common/sdk.ts — that was the source of the Could not find chainInfo for chain with id 534352 failures in client.test.ts.