feat: ConnectMultichain Singleton

[jiexi]

Explanation

This PR introduces a singleton pattern for the Multichain SDK that shifts the source of truth for connection status for downstream ecosystem clients (ConnectEVM, ConnectSolana) to the wallet_sessionChanged event.

1. Adds a singleton for the actual MetaMaskConnectMultichain instance itself with logic to merge incoming constructor options with the existing constructor options of the singleton

2. Removes the disconnect() on connect() pattern

3. Calling connect() while there is an inflight MWP connection results in a 'Existing connection is pending. Please check your MetaMask Mobile app to continue.' error being thrown

   • This mirrors the existing Default transport behavior in which multiple permission requests cannot be inflight at once (request of type wallet_requestPermissions already pending for origin...)

4. connect() is now additive and will combine the requested scopes and accounts with the existing (if any)

   • Also had to remove wallet_revokeSession call in DefaultTransport.connect()

5. disconnect() now supports partial revokes. If some scopes still remain after a partial revoke, the underlying connection remains intact and can be reused.

6. Fix/Adjust Browser Playground

   • Adds disconnect buttons to Browser playground cards
   • Fixes EVM Provider setChainId and setAccounts to also use the connect event
   • Removes the explicit ActiveProviderStorage pattern. Now all providers (cards) are "Active" even without user input to connect to a specific ecosystem
   • Multichain Card and button properly reflect initial instantiation connecting status

7. Makes wallet_sessionChanged the source of truth for ConnectEvm and future ecosystem clients

Addresses: https://consensyssoftware.atlassian.net/browse/WAPI-1066

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[adonesky1]

Screen.Recording.2026-02-05.at.2.20.51.PM.mov

EDIT

After testing further I see that even if my initial connection is with the legacy connector I see that same error 🤔

I'm starting to wonder whether we should even have this error "Requests cannot be made to chains not explicitly configured in supportedNetworks."

[jiexi]

PR desc updated

[adonesky1]

LGTM! Let's go!!! Amazing work Jiexi 🚀 🚀 🚀