feat: unified error type

[4t145]

Provide a unified error type.

1. create an unified error type named RmcpError, which can be converted from every possible error type when you create and operate a rmcp service.
2. remove error generice type of ClientInitializeError and ServerInitializeError, and use a new type called DynamicTransportError, witch include the transport type name.
3. make the transport error variant in ServiceError use DynamicTransportError too.
4. remove some redundant bound, precisely, all the From<std::io::Error> bound.

Motivation and Context

#299

How Has This Been Tested?

Breaking Changes

There is a little breaking change, I cancelled the error generic type in InitializeError. User can still fetch the inner transport error by using DynamicTransportError::downcast and DynamicTransportError::is. If user didn't match the inner type before, that would not be a problem.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

This change could make user confuse about the rmcp::Error and rmcp::RmcpError, so I added an deprecate marker on rmcp::Error.
And in 0.3.x, rmcp::RmcpError would become the rmcp::Error. The current rmcp::Error would become rmcp::ErrorData.

[Copilot]

Pull Request Overview

This PR unifies error handling by introducing a central RmcpError and a dynamic transport error type, DynamicTransportError, removing former generic error parameters and redundant bounds.

• Created RmcpError for all service, initialization, runtime, and transport-creation errors
• Replaced generic ClientInitializeError<E>/ServerInitializeError<E> with concrete types using DynamicTransportError
• Updated examples, tests, service modules, handlers, and macros to use ErrorData/RmcpError and removed old Error generics

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
examples/servers/src/common/counter.rs	Swapped alias Error as McpError → ErrorData as McpError
examples/clients/src/git_stdio.rs	Changed main to return Result<(), RmcpError> & added map_err
crates/rmcp/tests/test_progress_subscriber.rs	Updated return type from Error → ErrorData
crates/rmcp/tests/test_notification.rs	Updated return type from Error → ErrorData
crates/rmcp/tests/test_complex_schema.rs	Swapped Error as McpError → ErrorData as McpError
crates/rmcp/tests/common/handlers.rs	Swapped Error as McpError → ErrorData as McpError
crates/rmcp/src/transport.rs	Added Transport::name & DynamicTransportError type
crates/rmcp/src/service/tower.rs	Switched S::Error: Into<Error> → Into<ErrorData>
crates/rmcp/src/service/server.rs	Removed generic ServerInitializeError<E>, added helper
crates/rmcp/src/service/client.rs	Removed generic ClientInitializeError<E>, added helper
crates/rmcp/src/service.rs	Replaced Error generics, updated ServiceError variant
crates/rmcp/src/model/content.rs	Changed json methods to return ErrorData
crates/rmcp/src/lib.rs	Re-exported Error, ErrorData, RmcpError, deprecated old alias
crates/rmcp/src/handler/server/tool.rs	Updated parse_json_object & traits to use ErrorData
crates/rmcp/src/handler/server/router/tool.rs	Updated return types to ErrorData
crates/rmcp/src/handler/server/router.rs	Updated handler signatures to ErrorData
crates/rmcp/src/handler/server.rs	Swapped import Error as McpError → ErrorData as McpError
crates/rmcp/src/handler/client.rs	Swapped import Error as McpError → ErrorData as McpError
crates/rmcp/src/error.rs	Added RmcpError enum and transport_creation helper
crates/rmcp/README.md	Updated example to use ErrorData as McpError
crates/rmcp-macros/src/tool_handler.rs	Updated generated handlers to return ErrorData
crates/rmcp-macros/src/lib.rs	Updated doc comments to rmcp::ErrorData
crates/rmcp-macros/README.md	Updated macro examples to use ErrorData

Comments suppressed due to low confidence (4)

examples/servers/src/common/counter.rs:5

• [nitpick] Aliasing ErrorData as McpError can be misleading; consider using a direct alias like ErrorData or the unified RmcpError for clarity.

    ErrorData as McpError, RoleServer, ServerHandler,

crates/rmcp/src/transport.rs:248

• Consider adding unit tests for DynamicTransportError::is and downcast methods to ensure transport error conversion works as expected.

#[derive(Debug, thiserror::Error)]

crates/rmcp/README.md:18

• [nitpick] Update this example to use the new RmcpError alias instead of ErrorData for consistency with the unified error type.

use rmcp::{ErrorData as McpError, ServiceExt, model::*, tool, tool_router, transport::stdio, handler::server::tool::ToolCallContext, handler::server::router::tool::ToolRouter};

crates/rmcp/src/lib.rs:93

• [nitpick] Review whether the #[allow(deprecated)] on the re-export of Error is still necessary and remove it if the deprecation period is complete.

#[allow(deprecated)]

[Copilot]

This empty impl ServiceError {} block is redundant and can be removed to reduce clutter.

[jokemanfire]

conflict

[4t145]

@jokemanfire resolved

[4t145]

cc @ssddOnTop please check this

[ssddOnTop]

Thanks @4t145 I'll review this in a bit

[ssddOnTop]

There's some overall feedback at #299 (comment)

But the PR itself looks good to me.