respond to unknown requests with error

[kiftio]

What changes are you making?

When the checkout bridge receives a JSON-RPC request for an unsupported or unknown method, it now returns a proper JSON-RPC error response with code -32601 ("Method not found") instead of silently ignoring it. This applies across all three platforms (Android, Swift, and Web).

The distinction between requests (messages with an id field) and notifications (messages without an id field) is now respected per the JSON-RPC spec: only requests receive an error response, while notifications continue to be silently ignored.

How to test

1. Send a JSON-RPC message with an unsupported method and an id field (e.g. {"jsonrpc":"2.0","method":"ec.auth","id":"1","params":{}}) through the checkout bridge on any platform.
2. Verify that a JSON-RPC error response is sent back containing "code": -32601 and "message": "Method not found", with the matching id.
3. Send the same unsupported method without an id field (e.g. {"jsonrpc":"2.0","method":"ec.auth","params":{}}).
4. Verify that no response is sent back.
5. Verify that in both cases the message is not delegated to the client.

---

Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines
• I have read and agree with the Code of Conduct
• I've updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

---

Releasing a new Swift version?

• I have bumped the version in ShopifyCheckoutKit.podspec
• I have bumped the version in platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
• I have updated platforms/swift/CHANGELOG.md
• I have updated the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Android version?

• I have bumped the versionName in platforms/android/lib/build.gradle
• I have updated platforms/android/CHANGELOG.md
• I have updated the Gradle/Maven version snippets in platforms/android/README.md

Tip

See the Contributing documentation for the full release process per platform.

[kiftio]

• hide communication client #288
• remove buyer change in web #290
• Use typed Android JSON-RPC params #300
• Use typed Swift JSON-RPC envelopes #299
• respond to unknown requests with error #289 👈 (View in Graphite)
• ignore unknown messages #287
• main

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[github-actions]

Web — Coverage Report

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	98.52% (267/271)	88.55% (147/166)	100% (59/59)

[github-actions]

React Native — Coverage Report

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	91.66% (319/348)	87.86% (181/206)	100% (82/82)

[tiagocandido]

Soft non-blocking notes, mostly for consistency with the protocol spec:

• iOS may want to include ec.buyer.change as a supported notification too. It is a known protocol notification, so this keeps iOS from treating it like an unknown method.
• The new request-id check is useful for unknown methods. It may also be worth applying the same idea to supported request/response methods, so messages without an id stay fire-and-forget and do not get a response.
• For method-not-found responses, it may be safer to only echo string/number/null ids and use null for anything else. That avoids sending a JSON-RPC error response with an invalid id.

Keeping these soft because I do not think they need to block this PR.

[tiagocandido]

Approved. Left a few soft non-blocking notes for protocol consistency.