Change structured output error to Zod message

[robbie-thompson]

Summary

Currently the error message for all structured output parsing errors is "Model output doesn't fit required format". This is generic and doesn't surface any details of the underlying error - which is usually Zod erroring on the schema validation. In the case of Cloud hosting, this error isn't accessible anywhere.

This PR changes this, so that in the instance of a Zod error, the underlying schema error is shown to the user - so that the user has more info to go on.

Before:

After:

Related Linear tickets, Github issues, and Community forum posts

N/A

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[CLAassistant]

All committers have signed the CLA.

[n8n-assistant]

Hey @robbie-thompson,

Thank you for your contribution. We appreciate the time and effort you’ve taken to submit this pull request.

Before we can proceed, please ensure the following:
• Tests are included for any new functionality, logic changes or bug fixes.
• The PR aligns with our contribution guidelines.

Regarding new nodes:
We no longer accept new nodes directly into the core codebase. Instead, we encourage contributors to follow our Community Node Submission Guide to publish nodes independently.

If your node integrates with an AI service that you own or represent, please email [email protected] and we will be happy to discuss the best approach.

About review timelines:
This PR has been added to our internal tracker as "GHC-5763". While we plan to review it, we are currently unable to provide an exact timeframe. Our goal is to begin reviews within a month, but this may change depending on team priorities. We will reach out when the review begins.

Thank you again for contributing to n8n.

[cubic-dev-ai]

No issues found across 2 files

[robbie-thompson]

Hey @robbie-thompson,

Thank you for your contribution. We appreciate the time and effort you’ve taken to submit this pull request.

Before we can proceed, please ensure the following: • Tests are included for any new functionality, logic changes or bug fixes. • The PR aligns with our contribution guidelines.

Regarding new nodes: We no longer accept new nodes directly into the core codebase. Instead, we encourage contributors to follow our Community Node Submission Guide to publish nodes independently.

If your node integrates with an AI service that you own or represent, please email [email protected] and we will be happy to discuss the best approach.

About review timelines: This PR has been added to our internal tracker as "GHC-5763". While we plan to review it, we are currently unable to provide an exact timeframe. Our goal is to begin reviews within a month, but this may change depending on team priorities. We will reach out when the review begins.

Thank you again for contributing to n8n.

Confirming that tests are included, and PR aligns with contribution guidelines.