0.12.0

Description

Adds sampling-with-tools per SEP-1577, JSON Schema dialect declaration on tool schemas, server-side tool name validation, and capability extensions; fixes SSE reconnect on the same session and stops swallowing CancellationException.

Breaking Changes

Sampling messages can carry tool calls and results (SEP-1577) by @devcrocod in #718

SamplingMessage.content is now typed as a new SamplingMessageContent supertype, with MediaContent (text/image/audio), ToolUseContent, and ToolResultContent as variants. MediaContent still exists and now extends SamplingMessageContent, so most source code that constructs sampling messages compiles unchanged — but the binary signatures of SamplingMessage, CreateMessageResult, and related types have changed. ClientCapabilities.sampling is also now a typed Sampling object instead of a raw JsonObject. Recompilation is required; consumers reading sampling as JsonObject must migrate to the typed accessors.

watchosX64 and tvosX64 Kotlin/Native targets removed by @devcrocod in #727

These targets have been deprecated upstream. Migrate to the corresponding ARM/simulator targets (watchosArm64, watchosSimulatorArm64, tvosArm64, tvosSimulatorArm64).

Features

• Add $schema field to ToolSchema, declaring JSON Schema 2020-12 as the default dialect (SEP-1613) by @devcrocod in #696
• Validate tool names at registration time on the server, following the MCP tool naming standard (SEP-986) by @devcrocod in #695
• Add extensions field to ClientCapabilities and ServerCapabilities for advertising supported MCP extensions during the initialize handshake by @eritscher in #678

Fixed

• Validate the mcp-protocol-version HTTP header on initialization requests and correct DEFAULT_NEGOTIATED_PROTOCOL_VERSION to match the spec by @devcrocod in #697
• Propagate CancellationException instead of logging it as an error by @devcrocod in #706
• Evict stale GET SSE stream mapping on reconnect so a new GET on the same session is no longer silently rejected by the leftover entry from the previous stream by @amr in #716

Maintenance

• Add kotlinlang MCP server sample with search and get_page tools by @devcrocod in #713
• Migrate detekt to a buildSrc convention plugin with a fully explicit, version-locked YAML config by @devcrocod in #729
• Add Streamable HTTP integration tests for pagination, bad-request handling, and logging by @jskjw157 in #613
• Remove unused OpenAPI Generator plugin and configuration by @devcrocod in #683
• Remove Codecov configuration in favor of kover by @devcrocod in #691
• Remove redundant JUnit XML report configuration by @devcrocod in #728
• Remove IDEA files tied to the incompatible detekt IDE plugin by @devcrocod in #714
• Add Node.js setup to the release workflow so TypeScript integration tests run on macOS runners by @devcrocod in #684

Dependencies

• Kotlin to v2.3.21 in #704, #723
• kotlinx.serialization-json to v1.11.0 in #687

New Contributors

• @eritscher made their first contribution in #678
• @amr made their first contribution in #716

Full Changelog: 0.11.1...0.12.0