Fix: ensure Error classes are instantiated before raising

[hyongtao-code]

Fixes #27180

Previously, many raise XXXError statements were missing parentheses, causing exception classes to be raised instead of instances. This broke normal error propagation — error handlers, loggers, and response mappers could not access exception attributes or messages.

This patch standardizes all raise statements to instantiate the exception (raise XXXError()), restoring consistent error handling and preventing subtle runtime issues.

Summary

Screenshots

Checklist

• [ ] 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

[gemini-code-assist[bot]]

Summary of Changes

Hello @hyongtao-code, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a fundamental Python error handling pattern by ensuring that all exceptions are properly instantiated when raised. Previously, many raise statements were missing the necessary parentheses, leading to exception classes being raised directly instead of their instances. This oversight could cause issues with error propagation and prevent proper access to exception details. The changes standardize these statements, thereby restoring consistent and robust error handling across the application.

Highlights

• Standardized Exception Instantiation: All raise statements throughout the codebase have been updated to correctly instantiate exception classes by adding parentheses (e.g., raise MyError() instead of raise MyError).
• Improved Error Handling: This change ensures proper error propagation, allowing error handlers, loggers, and response mappers to correctly access exception attributes and messages, which was previously hindered by uninstantiated exception classes.
• Enhanced Code Robustness: By consistently instantiating exceptions, the system avoids subtle runtime issues and improves the overall reliability and predictability of error management.

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[hyongtao-code]

/gemini review