feat(fee-payer): upgrade to accounts SDK relay handler

[decofe]

Summary

Replaces Handler.feePayer from tempo.ts/server with Handler.relay from accounts/server (same handler wallet-next uses).

Why

The old tempo.ts handler lacks fee token resolution — clients had to manually set feeToken on the chain config or the transaction would be sent without one, causing FeeAMM swap errors even when validators accept pathUSD.

What changes

• Dependency: tempo.ts → accounts (already in workspace catalog at ~0.8.1)
• Handler: Handler.feePayer() → Handler.relay() with features: "all"
• Multi-chain: Transports for mainnet, moderato, and devnet (resolves chain from tx chainId)
• Fee token resolution: Relay auto-detects the best fee token from sender balances
• Auto-swap: Built-in cross-token fee payment when needed
• Simulation: Balance diffs + fee breakdown in eth_fillTransaction responses

Handler config

Handler.relay({
  cors: false,
  features: "all",
  feePayer: {
    account: privateKeyToAccount(env.SPONSOR_PRIVATE_KEY),
    name: "Tempo Sponsor",
    url: "https://sponsor.tempo.xyz",
  },
  transports: {
    [tempo.id]: http(env.TEMPO_RPC_URL ?? ...),
    [tempoModerato.id]: http(...),
    [tempoDevnet.id]: http(...),
  },
})

Backward-compatible

• API key auth, admin endpoints, rate limiting — all unchanged
• Open access at / still works
• Keyed access at /tp_* still works

[github-actions]

Cloudflare Deployments

App	Environment	Status	Preview
explorer	devnet	[OK] Deployed	View Preview
explorer	mainnet	[OK] Deployed	View Preview
explorer	testnet	[OK] Deployed	View Preview
fee-payer	devnet	[OK] Deployed	View Preview
fee-payer	moderato	[OK] Deployed	View Preview
fee-payer	privy	[OK] Deployed	View Preview
og	-	[OK] Deployed	View Preview
perf	-	[OK] Deployed	View Preview
reth-snapshots-viewer	-	[OK] Deployed	View Preview
tempo-snapshots-viewer	-	[OK] Deployed	View Preview
tokenlist	-	[OK] Deployed	View Preview

[github-actions]

Bundle Size Report

Metric	Size	Δ Change
Total	4.6 MB	+409.0 KB (+9.4%)
Gzip	1.3 MB	+121.8 KB (+9.8%)
Brotli	1.2 MB	+106.5 KB (+9.8%)

Chunk changes (>1KB)

Chunk	Change
assets/chains.js (removed)	-360.7 KB
assets/export-rate-limit.js (removed)	-177.3 KB
assets/wagmi.config.js	-29.5 KB
assets/AbiItem.js (removed)	-27.1 KB
assets/env.js	-9.7 KB
assets/validators.js (removed)	-5.1 KB
assets/call.js	+1.2 KB
assets/parseAbiItem.js (new)	+1.6 KB
assets/.js	+1.7 KB
assets/_address.js	+1.7 KB
assets/router.js	+1.9 KB
assets/known-event-totals.js (new)	+2.0 KB
assets/tempo-queries.js	+2.7 KB
assets/Addresses.js (new)	+9.1 KB
assets/schemas.js	+22.7 KB
assets/structs.js (new)	+23.9 KB
assets/queries.js	+26.4 KB
assets/Connectors.js (new)	+55.5 KB
assets/token.js	+56.1 KB
assets/manifest.js (new)	+173.8 KB
...and 2 more

Compared against main branch (baseline from 4/27/2026, 4:02:54 PM)