Update the serverFunctions.onError reference

[adipascu]

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Description(required)

Updates the serverFunctions.onError section added in #1609 with the rest of the contract. I wrote the option itself (solidjs/solid-start#2262), so these are the parts worth spelling out for anyone writing a handler:

• a thrown redirect reaches the export as a Response, so a handler that replaces everything it sees turns redirects into errors
• the return value is not awaited, so the export cannot be async
• only calls arriving over the network reach it, not a server function called during rendering, nor an API route

The example now guards thrown instanceof Response first, so it keeps working for anyone who adapts it, and reports through a monitoring SDK rather than console.error, which shows what the server-only bundling is for.

Checked against a running app: the same server function called over the network, during rendering, and in process from an API route, with only the network call reaching the handler.

Paired with solidjs/solid-start#2266, the same additions to the JSDoc for this option.

Related issues & labels

• Suggested label(s): documentation

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[adipascu]

Happy to trim if this reads too verbose for a reference entry.