feat: migrate tool schemas to kotlinx.schema

[Stream29]

Summary

Replace the SDK-specific ToolSchema model with kotlinx.schema.json.ObjectPropertyDefinition.

Fixes #300

Motivation and Context

The old ToolSchema models only a small subset of JSON Schema and requires callers to construct nested JsonObject values manually. Using kotlinx.schema provides a structured, serializable JSON Schema model that can be shared directly by MCP tool APIs.

How Has This Been Tested?

• npm ci in integration-test/src/jvmTest/typescript with Node.js 22.
• ./gradlew build --max-workers 3 --continue --rerun-tasks --no-configuration-cache on Linux (665 tasks).
• ./gradlew knit docs:classes docs:knitCheck --max-workers 3 --continue --rerun-tasks --no-configuration-cache on Linux (29 tasks).
• ./gradlew iosSimulatorArm64Test --max-workers 2 --continue --rerun-tasks --no-configuration-cache on macOS (49 tasks).
• MCP conformance v0.1.16 server, client, and auth workflows (275 checks passed, 0 failed).

Breaking Changes

Tool.inputSchema and Tool.outputSchema now use ObjectPropertyDefinition, and the SDK-specific ToolSchema type is removed. Callers constructing ToolSchema values must migrate to the corresponding kotlinx.schema.json property definitions.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

This removes the duplicate partial schema DTO from the SDK and delegates JSON Schema modeling and serialization to kotlinx.schema.

[Stream29]

@devcrocod @kpavlov This PR contains API breaking change. But I think it's reasonable.

[Copilot]

Pull request overview

This PR migrates the SDK’s tool schema representation from the SDK-specific ToolSchema DTO to kotlinx.schema.json.ObjectPropertyDefinition, aligning tool input/output schemas with a structured, serializable JSON Schema model used across MCP tool APIs.

Changes:

• Replaced ToolSchema with ObjectPropertyDefinition across core/server APIs, tests, samples, and conformance tooling.
• Updated tool schema construction to use kotlinx.schema.json property definitions (e.g., StringPropertyDefinition, NumericPropertyDefinition, $defs via defs).
• Added the kotlinx-schema-json dependency and updated public API dumps accordingly.

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
samples/weather-stdio-server/src/main/kotlin/io/modelcontextprotocol/sample/server/McpWeatherServer.kt	Updates sample tool schemas to kotlinx.schema.json definitions.
samples/simple-streamable-server/src/main/kotlin/io/modelcontextprotocol/sample/server/server.kt	Migrates sample server tool input schema to ObjectPropertyDefinition.
samples/kotlinlang-mcp-server/src/main/kotlin/org/kotlinlang/mcp/KotlinlangServer.kt	Migrates Kotlinlang sample tool schemas to ObjectPropertyDefinition.
README.md	Updates public documentation example to use ObjectPropertyDefinition/StringPropertyDefinition.
kotlin-sdk-server/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransportTest.kt	Adjusts server transport tests for new schema type.
kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt	Updates Server.addTool overload signature defaults to ObjectPropertyDefinition.
kotlin-sdk-server/api/kotlin-sdk-server.api	Reflects server public API change from ToolSchema to ObjectPropertyDefinition.
kotlin-sdk-core/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/types/ToolsTest.kt	Updates serialization/deserialization tests to validate kotlinx.schema.json schemas (including $defs).
kotlin-sdk-core/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/types/SamplingTest.kt	Updates sampling-related tool fixtures to new schema types.
kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/tools.kt	Replaces ToolSchema model with ObjectPropertyDefinition in the public Tool type and KDoc.
kotlin-sdk-core/build.gradle.kts	Adds kotlinx-schema-json as an API dependency for core public types.
kotlin-sdk-core/api/kotlin-sdk-core.api	Reflects core public API change (removal of ToolSchema, Tool signature updates).
kotlin-sdk-client/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/ClientSamplingValidationTest.kt	Updates client validation test fixtures to ObjectPropertyDefinition.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/ServerToolsTest.kt	Migrates integration tests to ObjectPropertyDefinition when registering tools.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/ServerToolsNotificationTest.kt	Updates notification integration tests for new schema type.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/ServerBulkFeaturesTest.kt	Updates bulk tool registration integration tests for new schema type.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/server/SamplingTest.kt	Migrates sampling integration tests to ObjectPropertyDefinition/property definitions.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/integration/typescript/http/KotlinServerForTsClientHttp.kt	Updates Kotlin server used by TS client tests to new schema construction.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/integration/streamablehttp/StreamableHttpClientTransportIntegrationTest.kt	Migrates streamable-http integration tool schemas to kotlinx.schema.json.
integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/integration/kotlin/AbstractToolIntegrationTest.kt	Migrates comprehensive tool-schema integration coverage to property-definition builders.
integration-test/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/ClientTest.kt	Updates client integration tests to use ObjectPropertyDefinition.
gradle/libs.versions.toml	Adds kotlinx-schema version and kotlinx-schema-json library entry.
conformance-test/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/conformance/ConformanceTools.kt	Updates conformance tool schemas to kotlinx.schema.json equivalents.

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[Stream29]

Some CIs are failing because the API breaking change. It's expected.