[isaacroldan]

WHY are these changes introduced?

shopify app dev exits when a client of the /extensions WebSocket sends a text message that is not valid JSON. getOnMessageHandler in packages/app/src/cli/services/dev/extension/websocket/handlers.ts calls JSON.parse on every message without a try/catch. The SyntaxError escapes the socket's message listener as an uncaught exception, and the process stops.

WHAT is this pull request doing?

• Catches the SyntaxError from JSON.parse, logs it with outputDebug, and ignores the message. Other errors still propagate.
• Adds a regression test in handlers.test.ts for a message that is not JSON.
• Adds a patch changeset for @shopify/app.

Before, a client that sends not json stops the dev session:

SyntaxError: Unexpected token 'o', "not json" is not valid JSON

After, the session continues. With --verbose, the CLI prints:

Ignoring websocket message that is not valid JSON: Unexpected token 'o', "not json" is not valid JSON

How to manually test your changes?

1. Run shopify app dev --verbose in an app with a UI extension.
2. Connect a WebSocket client to the dev server at /extensions, for example npx wscat -c ws://localhost:<port>/extensions.
3. Send the text not json.
4. Confirm that app dev keeps running and prints the debug line above.
5. Send a valid message, for example {"event":"dispatch","data":{"type":"focus","extensions":[]}}, and confirm that the connected clients receive it.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[alexanderMontague]

Approving — the fix is correct for what it claims. A SyntaxError thrown inside the message listener is an uncaught exception (it never becomes a socket error event, so #9039 doesn't cover it), and rethrowing non-SyntaxErrors is the right call.

One suggestion worth doing here rather than in a third PR: the guard only catches invalid JSON. Valid JSON with the wrong shape still throws a TypeError from the same listener and exits app dev. I checked these against the handler logic:

• null → Cannot destructure property 'event' of 'jsonData' as it is null
• {"event":"log"} → Cannot read properties of undefined (reading 'extensionName')
• {"event":"update"} → Cannot read properties of undefined (reading 'app')

A small extension closes this: after parsing, return early unless jsonData is a non-null object, and treat a missing data on log/update as ignorable.

Process nit: this and #9039 are both branched from main, touch the same two files, and fix the same "misbehaving client kills app dev" problem. I confirmed they merge cleanly together, so this is only a question of whether one PR would be easier to review and release-note.

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