MCP: Validate tool name uniqueness across BuiltIn and Custom tools

[Copilot]

Why make this change?

MCP tool names must be unique. Without validation, custom tools (generated from stored procedure entities) could conflict with built-in tools (create_record, read_records, etc.) or other custom tools, causing undefined behavior during tool invocation.

What is this change?

Added duplicate detection in McpToolRegistry.RegisterTool() that throws DataApiBuilderException on conflict:

// Check for duplicate tool names
if (_tools.TryGetValue(metadata.Name, out IMcpTool? existingTool))
{
    string existingToolType = existingTool.ToolType == ToolType.BuiltIn ? "built-in" : "custom";
    string newToolType = tool.ToolType == ToolType.BuiltIn ? "built-in" : "custom";
    
    throw new DataApiBuilderException(
        message: $"Duplicate MCP tool name '{metadata.Name}' detected. " +
                 $"A {existingToolType} tool with this name is already registered. " +
                 $"Cannot register {newToolType} tool with the same name. " +
                 $"Tool names must be unique across all tool types.",
        statusCode: HttpStatusCode.ServiceUnavailable,
        subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
}

Files Modified:

• McpToolRegistry.cs: Added validation in RegisterTool()

Files Added:

• McpToolRegistryTests.cs: 12 test cases covering duplicate detection across tool types, case sensitivity, and error messaging

Validation occurs during McpToolRegistryInitializer.StartAsync() ensuring fail-fast at service startup.

How was this tested?

• Unit Tests

Sample Request(s)

N/A - Internal validation, no user-facing API changes

Original prompt

---

This section details on the original issue you should resolve

<issue_title>MCP-CustomTool: Handle duplicate tool names, if any</issue_title>
<issue_description>MCP tool names should be unique. Custom tools when configured and exposed should not be duplicate and conflict with existing tool names.

• MCP tools should not be duplicate
• Tools of both types- BuiltInTool and DynamicCustomTool should be unique
• This should be detected and validated during tools registration
• Appropriate error message should be provided to user if that happens so that user can fix it
• Add supporting tests with good code coverage and different scenarios and edge cases</issue_description>

<agent_instructions>- Refer to the description and comments

• Implement the changes and make sure existing functionality is not broken
• Create a Pull Request</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@JerryNixon Remember tool names are based on Entity aliases which are already required to be unique.

• Fixes MCP-CustomTool: Handle duplicate tool names, if any #3049

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[Copilot]

Pull request overview

This PR adds validation to ensure MCP tool names are unique across both built-in and custom tool types. Without this validation, custom tools (generated from stored procedure entities) could conflict with built-in tools like create_record or read_records, causing undefined behavior during tool invocation.

Changes:

• Added duplicate tool name detection in McpToolRegistry.RegisterTool() that throws DataApiBuilderException when a conflict is detected
• Implemented comprehensive test suite with 12 test cases covering various duplicate scenarios, case sensitivity, and error messaging

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Azure.DataApiBuilder.Mcp/Core/McpToolRegistry.cs	Added validation logic to detect and reject duplicate tool names across BuiltIn and Custom tool types
src/Service.Tests/Mcp/McpToolRegistryTests.cs	New test file with comprehensive coverage of duplicate detection scenarios, case sensitivity, and edge cases

[anushakolan]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

[Aniruddh25]

Reducing the test matrix to what is really possible.

[Aniruddh25]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).