feat: add extensions attribute to ClientCapabilities and ServerCapabilities - #1064
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YousefHaggy wants to merge 3 commits into
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feat: add extensions attribute to ClientCapabilities and ServerCapabilities#1064YousefHaggy wants to merge 3 commits into
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Add the optional `extensions` field to `ClientCapabilities`, mirroring the MCP extensions framework (SEP-2133) as declared in the draft schema and already shipped by the TypeScript, Python, C#, Go, Rust, and Kotlin SDKs. Keys are extension identifiers (e.g. "io.modelcontextprotocol/oauth-client-credentials") and values are per-extension settings objects; an empty object indicates support with no settings. The field is optional, defaults to null, and is omitted from the wire when unset, so it is backward compatible with existing peers. Follows CONTRIBUTING.md "Evolving wire-serialized records" Case A: the new component is appended, annotated with @JsonProperty, boxed/nullable, and the prior 4-arg constructor is retained as a source-compatible overload. Adds a builder `extensions(Map)` setter plus an `extension(id, settings)` helper that normalizes null settings to an empty object. Includes the required absent/omit/unknown-field tests plus a round-trip test in SchemaEvolutionTests. Refs modelcontextprotocol#785 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Mirror the ClientCapabilities `extensions` change on ServerCapabilities, as the MCP extensions framework (SEP-2133) declares the field on both capability objects. Same Case A treatment: appended optional component, retained 6-arg constructor overload, builder `extensions(Map)` + `extension(id, settings)` helper, and `mutate()` carries the new field. Adds absent/omit/round-trip tests in SchemaEvolutionTests. Refs modelcontextprotocol#785 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Keep only the whole-map extensions(Map) setter on both capability builders, matching the existing experimental(Map) convention. The per-entry extension(id, settings) helper was a novel API for a single field, duplicated verbatim across both builders, with copy-on-write merge semantics no sibling setter has. Callers pass Map.of(id, Map.of()) for "supported, no settings". Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Note: Merge as part of 2026-07-28 ; squash-merge |
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Add the optional extensions field to ClientCapabilities and ServerCapabilities, mirroring the MCP extensions framework (SEP-2133) as declared in the draft schema and already shipped by the TypeScript, Python, C#, Go, Rust, and Kotlin SDKs.
Refs #785
Motivation and Context
Spec + cross-SDK precedent
draft schema — schema/draft/schema.ts#L785
(server twin at #L882) —
introduced by SEP-2133
(merged into the spec 2026-01-26). Type: { [key: string]: object }. Keys are
extension identifiers following _meta naming rules; an empty object means
"supported, no settings". See also the
extensions overview docs.
SDK without it:
How Has This Been Tested?
Added 3 tests per new field per the contributing guidelines.
Breaking Changes
No breaking changes
Types of changes
Checklist
Additional context