refactor(server): standardize tool error handling and status code mapping

[duwenxin99]

• Detect errors and return error codes accordingly in the tool call handler functions.
• Replace the old util.ErrUnauthorized with the new Toolbox error type.

[gemini-code-assist]

Summary of Changes

Hello @duwenxin99, I'm Gemini Code Assist¹! 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 significantly refactors the server's error handling logic, particularly for tool invocation and authentication-related issues. By introducing a new error hierarchy, the changes aim to standardize how errors are categorized and how corresponding HTTP status codes are determined and returned to clients. This improves the clarity and consistency of error responses across the server.

Highlights

• Standardized Error Handling: Introduced a new structured error handling mechanism using ToolboxError, AgentError, and ClientServerError types to categorize and manage errors more effectively.
• Improved HTTP Status Code Mapping: Refactored the server's API and MCP handlers to map internal errors to appropriate HTTP status codes (e.g., 401, 403, 500) based on the new error categories, moving away from string-based error matching.
• Removed util.ErrUnauthorized: Replaced direct usage of the generic util.ErrUnauthorized error with the more specific util.NewClientServerError which includes an explicit HTTP status code.
• Consistent Authentication Error Propagation: Ensured that authentication errors (401/403) are consistently handled and propagated, distinguishing between client credential issues and internal configuration problems.

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[gemini-code-assist]

Code Review

This pull request refactors error handling to use a standardized, typed-error approach, which is a great improvement over string-based error checks. However, the implementation has introduced several critical and high-severity bugs. Specifically, there's an incorrect usage of errors.Is that will break authentication error checks, and multiple places where authorization checks are bypassed because of missing return statements. Additionally, error handling logic for tool.Invoke is incomplete, failing to handle errors that are not of the new custom ToolboxError type. These issues need to be addressed to ensure the server behaves correctly.

[Yuan325]

Might want to merge this into a branch first instead of main if the tests will fail before refactoring other parts of Toolbox? Seems like the err branch is merging into main, and once that is merged, this PR will be updated to merge into main.

[duwenxin99]

Might want to merge this into a branch first instead of main if the tests will fail before refactoring other parts of Toolbox? Seems like the err branch is merging into main, and once that is merged, this PR will be updated to merge into main.

@Yuan325 I'm going to merge this refactor PR into this branch first: #2403

[duwenxin99]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors and standardizes error handling across the server by introducing custom error types (AgentError, ClientServerError), aiming for improved maintainability and correctness. However, a critical security concern has been identified: the refactoring introduces a consistent pattern of exposing detailed internal error messages to the client for internal server errors (HTTP 500). This information exposure could be exploited by attackers to gain insights into the application's internal workings. Additionally, there are a few minor issues related to error message formatting and a potentially unhandled error.