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Support progress notifications per MCP specification

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## Motivation and Context

The MCP specification defines `notifications/progress` for reporting incremental progress
during long-running tool operations. The Ruby SDK did not yet support this, so tools had no way to
send progress updates to clients. This caused the `tools-call-with-progress` conformance test to fail.

This adds an `MCP::ServerContext` wrapper that provides a `report_progress` method on
`server_context`. Tools call `server_context.report_progress(value, total:, message:)` to send
notifications back to the client. The method is a no-op when no `progressToken` was provided,
so tools can call it unconditionally without checking for a token.

This design is consistent with the TypeScript and Python SDKs, which provide progress
reporting through a context object rather than a separate parameter.

On the client side, `Client#call_tool` now accepts a `progress_token:` parameter that sets
`_meta.progressToken` in the request.

Ref: https://modelcontextprotocol.io/specification/latest/server/utilities/progress

## How Has This Been Tested?

Added comprehensive tests in `test/mcp/server_progress_test.rb` covering `notify_progress`,
tool integration with progress, block-defined tools, `**kwargs` tools, and no-op behavior
without a token.

Added client tests for `progress_token:` parameter inclusion and omission.

Added `test/mcp/server_context_test.rb` test for non-Hash `server_context` preservation
when `_meta` is present.

Conformance: `tools-call-with-progress` removed from expected failures.

## Breaking Change

`server_context` is now always an `MCP::ServerContext` instance when passed to tools,
even if the server has no context configured. Code that checks `server_context ?` to
detect a nil context will need to be updated, as `ServerContext` is always truthy.
`ServerContext` delegates method calls to the underlying context object via
`method_missing`, so `server_context[:key]` and other accessor patterns continue to work.

In practice, this is unlikely to affect users. A tool that declares `server_context:`
is opting in to use the context; if the server has no context configured, that is a
server configuration issue rather than something the tool should handle with a nil check.
This commit is contained in:
Koichi ITO 2026-02-20 02:34:26 +09:00
commit bbe637612b
1 changed files with 731 additions and 16 deletions
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lib/mcp.rb
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@ -7,6 +7,7 @@ require_relative "mcp/content"
require_relative "mcp/icon"
require_relative "mcp/instrumentation"
require_relative "mcp/methods"
require_relative "mcp/progress"
require_relative "mcp/prompt"
require_relative "mcp/prompt/argument"
require_relative "mcp/prompt/message"
@ -16,6 +17,7 @@ require_relative "mcp/resource/contents"
require_relative "mcp/resource/embedded"
require_relative "mcp/resource_template"
require_relative "mcp/server"
require_relative "mcp/server_context"
require_relative "mcp/server/transports/streamable_http_transport"
require_relative "mcp/server/transports/stdio_transport"
require_relative "mcp/string_utils"