across-snowbridge: route + builder for L2 → Hydration

[mrq1911]

Summary

Adds an end-to-end Across-Snowbridge bridge-of-bridges route: Across V3 fast-fill on a supported L2 (Base) → Snowfork's deployed SnowbridgeL2Adaptor.sendTokenAndCall on the L2 → Across MulticallHandler on Ethereum → Uniswap V3 swap to fund the Snowbridge fee → Gateway.v2_sendMessage → AssetHub → XCM InitiateTransfer to Hydration.

Based on feat/snowbridge-v2 to reuse the native polkadot-api XCM construction; no runtime dep on @snowbridge/api.

Commits

xc-core Across primitive + L1/L2 Adaptor ABIs + Arb/Op chain configs	scaffolding
xc-cfg Across-Snowbridge builder (sendTokenAndCall + sendEtherAndCall)	SCALE-encoded V5 XCM via Snowbridge V2 helpers
Uniswap V3 exactOutputSingle calldata + Quoter ABI	live-verified against mainnet
FeeAmountBuilder.AcrossSnowbridge.calculateFee	composes Snowbridge inbound + Uniswap Quoter
Across /suggested-fees HTTPS call at contract build time	amount-dependent relayer fee
Base USDC → Hydration + Base ETH → Hydration route templates	Tag.Across_Snowbridge
Changeset (minor bump for xc-core / xc-cfg / xc-sdk)
Chopsticks integration spec	XCM weight-check on AssetHub + Hydration

Test plan

Unit: npm test in packages/xc-core (26 specs) and packages/xc-cfg (26 specs) — all green.

Live preflight checks (run from CLI):

1. Across /suggested-fees — passes; 100 USDC Base→Eth returns relayer fee 306,761 (~0.31 USDC), fill time 2s, SpokePool addresses match our chain configs.
2. Uniswap V3 Quoter — passes; USDC/WETH pool fee 500 valid on Ethereum mainnet, quoteExactOutputSingle returns sane price.

Chopsticks XCM dry-run (in integration-tests/xc-test):

npm run spec:across-snowbridge

Forks AssetHub + Hydration via chopsticks, builds the contract call, decodes SendParams.xcm, runs XcmPaymentApi.query_xcm_weight on both chains. 5/5 pass in ~37 s with:

🥢 AssetHub weight: refTime=1,182,518,000, proofSize=21,000
🥢 Hydration remote_xcm weight: refTime=300,000,000, proofSize=0

Confirms the V5 XCM bytes decode cleanly and every instruction's weighter resolves on both chains.

What's deferred (follow-up PRs)

• anvil-forked Base sendTokenAndCall simulation — last remaining preflight gate before mainnet canary
• Arbitrum + Optimism route templates — chain configs exist on this branch (xc-cfg/chains/evm/arbitrum.ts, optimism.ts) and SWAP_REGISTRY includes USDC entries, but no route wiring yet
• Additional asset coverage on Base (USDT / WBTC / DAI / WETH)
• Outbound SnowbridgeL1Adaptor.depositToken builder — gated on L1Adaptor funding-model decision

Rebase note

Sits on feat/snowbridge-v2. Once that merges to master, this rebases cleanly onto master with no expected conflicts.

[changeset-bot]

🦋 Changeset detected

Latest commit: cf5318e

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

This PR includes changesets to release 3 packages

Name	Type
@galacticcouncil/xc-core	Minor
@galacticcouncil/xc-cfg	Minor
@galacticcouncil/xc-sdk	Minor

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[github-actions]

🧚 Live preview: galacticcouncil/hydration-ui#3800