feat: agent tool variants, server tools, multi tool-result helper

[rimdoo]

Summary

• AgentTool.Other constructor now public. The documented escape hatch ("pass any Java SDK AgentCreateParams.Tool") was previously unreachable from outside the module because of an internal constructor. raw property stays internal.
• Typed variants for the common Managed-Agents tool cases:
  • AgentTool.Toolset20260401Subset(enabled: Set<DefaultTool>) — subset of agent_toolset_20260401 via default_config.enabled = false + per-tool addConfig. DefaultTool enum: BASH, READ, GLOB, GREP, WEB_SEARCH, WEB_FETCH.
  • AgentTool.McpToolset(serverName, enabled?) — reference a registered MCP server, optional tool-name whitelist.
  • AgentTool.CustomTool(name, description, rawInputSchema) — client-side tools; rawInputSchema keeps the Java SDK type so nested JSON Schema is fully expressible.
• Surrounding additions used by the same flows:
  • McpUrlServer(name, url) + createAgent(mcpServers = ...) register remote MCP servers at agent creation. Auth lives separately in a vault credential targeting the same mcpServerUrl.
  • createSession(vaultIds = ...) attaches vault credentials so the agent can authenticate to MCP servers.
  • SessionStreamEvent.AgentCustomToolUse(id, name, inputJson) — previously absorbed by SessionStreamEvent.Other.
• Message.toolResults(vararg | List) — bundles multiple tool_result blocks into one user message (required when the assistant emits >1 tool_use per turn).
• ServerTool sealed (WebSearch / WebFetch) + serverTools parameter on createMessage / streamMessage. Mixes freely with client-side tools = listOf(Tool(...)).

Scoping notes

• Messages-API MCP (mcp_servers body + anthropic-beta: mcp-client-2025-04-04 header) is not wrapped here. The upstream surface is still moving, so callers use the raw Java SDK directly for that case.
• Audited every class X internal constructor(internal val raw: ...) in sdk/src/main/kotlin/com/rimdoo/anthropic/. The only one that should accept external raw injection is AgentTool.Other; the rest (ContentBlock.Other, SessionStreamEvent.Other, MessageStreamEvent.MessageStart/...) are response-side wraps the SDK constructs itself, so internal constructor is correct on those.

Test plan

• ./gradlew :sdk:test — 134 unit tests pass (39 mappers, 7 DSL, 7 exceptions, 81 client-API smoke).
• New MappersTest entries: every AgentTool variant builds, Toolset20260401Subset / McpToolset reject empty enabled sets, McpUrlServer + ServerTool.WebSearch + ServerTool.WebFetch build with every option combination, AgentTool.Other(rawUnion) constructs from outside-style code.
• New ClientApiSmokeTest entries: createAgent with every AgentTool variant + mcpServers, createSession with vaultIds, createMessage / streamMessage with serverTools (alone and mixed with tools).

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