Bridge FOX to Arbitrum fails — Relay may not support FOX pair

[premiumjibles]

Problem

Bridging FOX token to Arbitrum is broken in the agentic app. The app only has two swap providers: Relay (cross-chain) and Bebop (same-chain). All cross-chain/bridge operations depend solely on Relay. If Relay doesn't support FOX Ethereum→Arbitrum, the swap fails with "No rates available."

tk ticket: sa-delf

Root Cause

• fetchBestSwapRate() in initiateSwap.ts always calls Relay for cross-chain; no fallback provider exists
• The main ShapeShift web app has a dedicated ArbitrumBridgeSwapper using @arbitrum/sdk that handles this — but it's NOT integrated in the agentic app
• FOX on Arbitrum (0xf929de51D91C77E42f5090069E0AD7A09e513c73) is critical for rFOX staking

Fix Approaches

1. Verify Relay support for the FOX pair first
2. Port ArbitrumBridgeSwapper from main app as additional provider in fetchBestSwapRate()
3. Add another cross-chain provider as fallback (THORChain, Chainflip, etc.)

Key Files

• apps/agentic-server/src/tools/initiateSwap.ts — fetchBestSwapRate() (lines 52-99)
• apps/agentic-server/src/utils/getRelayRate/getRelayRate.ts
• packages/swapper/src/swappers/ArbitrumBridgeSwapper/ (shapeshift repo, reference)

Acceptance Criteria

• User can bridge FOX from Ethereum to Arbitrum via agentic chat
• Clear error messages if bridging unavailable for a token pair
• Tests cover the new bridge path