fix: surface error when wallet is on an unsupported chain in SignIn

[sulhadin]

Summary

Some users got stuck on the Sign In screen with no feedback: clicking "Sign message" did nothing, no error, no log, no state change.

The reason is the early return in SignIn.signIn:

const chainId = activeChain?.id;
const { nonce } = state;

if (!address || !chainId || !nonce) {
  return;
}

When useAccount().chain?.id is undefined (the wallet is connected on a chain that is not in the configured chains list), this branch silently returns. The user has no idea why the button doesn't work.

This PR keeps the !address and !nonce branches as silent returns (those are transient or wagmi-level concerns and the button is already disabled while the nonce is loading), but splits out !chainId into its own branch that surfaces an actionable error:

Your wallet is on an unsupported network. Switch to a supported network and try again.

Changes

• packages/rainbowkit/src/components/SignIn/SignIn.tsx — split the silent bail; surface sign_in.signature.unsupported_chain_error when chainId is missing.
• packages/rainbowkit/src/locales/en_US.json — add the new key.
• packages/rainbowkit/src/components/SignIn/SignIn.test.tsx — add a unit test that mocks useAccount to return chain: undefined and asserts the error message is rendered and that neither createMessage nor signMessageAsync is called.
• .changeset/ — patch changeset describing the user-facing change.

How to reproduce the original behavior

1. Build a dApp that configures wagmi with a single chain (e.g. chains: [mainnet]).
2. Connect via WalletConnect from a mobile wallet whose active network is anything other than that chain (e.g. Sepolia or Polygon).
3. The Sign Message screen appears. Clicking the button does nothing — no error, no log, no UI change.

With this PR, the user sees the unsupported-network error message and can act on it.

Test plan

• pnpm test:unit run -t SignIn — 4 tests pass (3 existing + 1 new).
• pnpm lint — clean.
• Only the en_US.json locale file is modified, in line with the contribution guidelines.

Notes

• Only the !chainId case is split out; the other two (!address, !nonce) keep their original silent-return behavior since the button is already disabled in those cases.
• Open to alternative wording for the error message if you prefer it shorter or differently phrased.

[changeset-bot]

🦋 Changeset detected

Latest commit: d0b3296

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

This PR includes changesets to release 18 packages

Name	Type
@rainbow-me/rainbowkit	Patch
example	Patch
@rainbow-me/rainbow-button	Patch
rainbowkit-next-app	Patch
site	Patch
with-create-react-app	Patch
with-next-app-i18n	Patch
with-next-app	Patch
with-next-custom-button	Patch
with-next-mint-nft	Patch
with-next-siwe-iron-session	Patch
with-next-siwe-next-auth	Patch
with-next-wallet-button	Patch
with-next	Patch
with-react-router	Patch
with-remix	Patch
with-vite	Patch
with-next-rainbow-button	Patch

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