Expected Behavior

• There is a Progress Flow spec on MCP.
• When the client sends the params._meta.progressToken, the server may send progress notifications.

Current Behavior

• The SDK doesn't supports it currently

Context

• Some clients times out when there is no progress event from server.
• Of course the specification says "MAY", but it is also true that server doesn't supports the spec.
• Also, when the tool task is long task, the UX can lead to bad, that can't tell if it's stuck or not.

Related tasks:

• Fix the Tool Call handling to allow processing additional metadata parameters from the full CallToolRequest object, enabling features like progress tracking. feat: refactor the tool specifications #351 -> replaced by refactor: deprecate tool spec's arguments-only handler in favor of CallToolRequest #375
• Extend the McpSchema to include the _meta and _meta.progressToken parameters to all Request types. feat: add progress token support and extend Request interface #352
• Implement McpServer to McpClient progress notification, extending the exchange implementations. The Support Progress Flow for McpServer #300 is partially related.
• Implement the McpClient to McpServer progress notifications. Support Progress Flow for McpClient #389
• Implement McpServer and McpClient progress notification. feat: Support Progress Flow #407