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Extend resolver DI to sampling and roots requests (#3049)

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Max 2026-07-06 18:25:57 +01:00 • committed by GitHub
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docs/migration.md
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@ -697,6 +697,24 @@ and raises `RuntimeError` if the resource requests input.
The internal layers (`ToolManager.call_tool`, `Tool.run`, `Prompt.render`, `ResourceTemplate.create_resource`, etc.) now require `context` as a positional argument.
### Resolver-routed requests require the client capability on every protocol version
A v1 server could send elicitation, sampling, and roots requests to clients
that never declared the matching capability; only tools-bearing sampling was
checked. In v2 the `Resolve(...)` markers (`Elicit`, `Sample`, `ListRoots`)
enforce the spec's egress rule: an undeclared capability (form-mode `elicitation`,
`sampling`, or `roots`, plus `sampling.tools` when the request carries `tools`
or `tool_choice`) fails the call with a `-32021`
`MISSING_REQUIRED_CLIENT_CAPABILITY` JSON-RPC error instead of sending a
request the client cannot handle. This applies on 2025-11-25 sessions with a
live back-channel too; a session with no back-channel keeps failing with its
no-back-channel error. To migrate, declare the capability: the SDK client
declares `elicitation`, `sampling`, and `roots` when the matching callback is
set, and `sampling.tools` needs an explicit
`Client(sampling_capabilities=SamplingCapability(tools=...))`. Direct
`ctx.elicit()` and `ctx.session.*` calls outside resolvers keep their previous
behavior, including the pre-existing tools check on `create_message`.
### `MCPError` raised from an `@mcp.tool()` handler now surfaces as a JSON-RPC error
Raising `MCPError` (or any subclass) inside an `@mcp.tool()` handler now