Gate play on Base Sepolia and offer one-click network switch

[heyradcode]

Why

A wallet on any network other than Base Sepolia left the app in a dead state
with no way out:

• The network switcher returned null whenever useAccount().chain was
  undefined, which is exactly the state an unsupported network puts it in. The
  one control that could switch back was hidden.
• Native balance reads failed for the same reason: useBalance({ address })
  targeted a chain wagmi had no transport for.
• Hardhat Local sat first in CHAINS, and wagmi treats chains[0] as its
  default, so hosted builds fell back to http://localhost:8545 for RPC reads
  before a wallet reported a usable chain.

MetaMask defaults to Ethereum Mainnet, so a new player hit all three at once.

What changed

Chain list (constants/chains/ethereum.ts)

• Base Sepolia first, so the default RPC target is the chain we deploy to.
• Hardhat Local only under import.meta.env.DEV.
• Removed Arbitrum, Optimism, and Base mainnet. None have contracts, so
  offering them let a player switch to a network where every read silently
  fails.
• Added TARGET_CHAIN_ID (from VITE_EVM_CHAIN_ID, default 84532) and
  isSupportedChain(). Declared VITE_EVM_CHAIN_ID in vite-env.d.ts, where
  it was already being read but undeclared.

Network switcher

• Keyed off chainId (raw, defined whenever connected) instead of chain
  (only set for configured chains), so it stays visible and reads
  "Wrong network".
• Dropped the mainnet/testnet toggle, which had nothing left to toggle.

New NetworkGate

• Banner under the top bar with a single "Switch to Base Sepolia" action.
• switchChain sends wallet_switchEthereumChain; wagmi's injected connector
  retries with wallet_addEthereumChain on MetaMask error 4902, so a player who
  has never added Base Sepolia gets the add prompt from the same button.
• Falls back to Dynamic's primaryWallet.switchNetwork() when the wagmi bridge
  isn't connected yet.
• Translates error 4001 into a readable message instead of a raw wallet error.
• Renders nothing unless an EVM wallet is connected, so Solana-only players
  never see it.

Testing

pnpm --filter frontend lint:check, test, and build all pass
(42 files / 281 tests).

Two existing test files covered the changed API and were updated; 11 tests were
failing against the old getChainsByType helpers and chain mock. Added a
regression test that the switcher stays visible on an unsupported chain, plus
six tests for the gate covering the Dynamic fallback and the rejection path.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
do-not-stop-frontend	Ready	Preview, Comment	Jul 25, 2026 3:04pm
do-not-stop-website	Ready	Preview, Comment	Jul 25, 2026 3:04pm

[github-actions]

🧪 Coverage

Package	Statements	Branches	Functions	Lines	Overall
backend	81.44% (869/1067)	75.13% (405/539)	83.41% (181/217)	82.88% (809/976)	80.89% (2264/2799)
frontend	67.00% (1245/1858)	67.57% (1038/1536)	63.00% (298/473)	67.55% (1135/1680)	66.99% (3716/5547)
shared	59.35% (1491/2512)	58.10% (900/1549)	59.07% (267/452)	62.31% (1379/2213)	60.02% (4037/6726)

[aichannode]

LGTM! thank you 👍