robust for json parser

[zxfishhack]

Summary

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extract first valid JSON from arguments.

Fixes #17686 .

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Checklist

[!IMPORTANT]
Please review the checklist below before submitting your pull request.

• [ ] This change requires a documentation update, included: Dify Document
• [x] I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

Please fix the tests.

[laipz8200]

Hi @zxfishhack, Thank you for your contribution! Could you please add some unit tests for this enhancement?