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feat(appkit): add FunctionTool, HostedTool types and MCP client#283

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MarioCadenas wants to merge 1 commit intoagent/1-shared-types-adaptersfrom
agent/2a-tool-types-mcp
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feat(appkit): add FunctionTool, HostedTool types and MCP client#283
MarioCadenas wants to merge 1 commit intoagent/1-shared-types-adaptersfrom
agent/2a-tool-types-mcp

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@MarioCadenas MarioCadenas commented Apr 16, 2026

Summary

  • FunctionTool: user-defined tools with JSON Schema + execute callback
  • HostedTool: union of Genie, VectorSearch, custom MCP, and external connection configs
  • AppKitMcpClient: minimal JSON-RPC 2.0 client using raw fetch (zero deps)
  • Type guards (isFunctionTool, isHostedTool) and definition converters
  • resolveHostedTools maps HostedTool configs to Databricks MCP endpoint URLs
  • 25 tests covering type guards, definition builders, and URL resolution

PR Stack

  1. Shared types + Adapters — feat(appkit): add shared agent types and LLM adapter implementations #282
  2. Tool types + MCP client (this PR)
  3. Agent plugin core + ToolProvider implementations — feat(appkit): add agent plugin core and ToolProvider implementations #284
  4. PluginContext mediator — feat(appkit): add PluginContext mediator for inter-plugin communication #285
  5. createAgent + agent-app + docs (v1) — feat(appkit): add createAgent wrapper, agent-app, and API docs #286
  6. Plugin context-binding separation — refactor(appkit): separate plugin context binding from plugin construction #293
  7. agents() plugin + createAgent(def) + .toolkit()feat(appkit): add agents() plugin, createAgent() factory, and .toolkit() #294
  8. agent-app + docs migrated to agents()feat(appkit): migrate agent-app and docs to the new agents() plugin #295
  9. Relocate shared agent utilities — refactor(appkit): relocate shared agent utilities into plugins/agents #296
  10. preparePlugins forwards eager instance — refactor(appkit): forward eager plugin instance through preparePlugins #297
  11. fromPlugin() API — feat(appkit): add fromPlugin() for referencing plugin tools in code-defined agents #298
  12. Retire deprecated agent() + createAgentAppchore(appkit): remove deprecated agent() plugin and createAgentApp shortcut #299
  13. Retire toPluginWithInstance + bug fixes — refactor(appkit): retire toPluginWithInstance; consolidate on fromPlugin + fix schema/routing bugs #300

Test plan

  • 1610 tests pass
  • Typecheck clean
  • Biome lint clean

Add explicit tool type definitions and a lightweight MCP client:

- FunctionTool: user-defined tools with JSON Schema parameters + execute
- HostedTool: Genie, VectorSearch, custom/external MCP endpoint configs
- AppKitMcpClient: zero-dependency JSON-RPC 2.0 client over HTTP fetch
- Type guards (isFunctionTool, isHostedTool) and definition converters
- resolveHostedTools maps HostedTool configs to MCP endpoint URLs
- Test coverage for type guards, definition builders, and URL resolution

Also add ergonomic helpers for defining tools at the app layer:

- tool(): Zod-powered factory for function tools. Generates JSON Schema
  via z.toJSONSchema(), infers execute() arg types from the schema, and
  wraps execution with safeParse so invalid args return an LLM-friendly
  error string instead of throwing.
- mcpServer(name, url): concise factory for custom MCP server tools,
  replacing the verbose { type, custom_mcp_server: { app_name, app_url } }
  wrapper.
- Promote zod from optional peer dep to runtime dep (^4.0.0) so tool()
  and z.toJSONSchema() are always available.

Signed-off-by: MarioCadenas <MarioCadenas@users.noreply.github.com>
@MarioCadenas
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Superseded by the v2 6-PR stack:

  1. Shared agent types + LLM adapters — feat(appkit): shared agent types and LLM adapter implementations #301
  2. Tool primitives + ToolProvider surfaces — feat(appkit): tool primitives and ToolProvider surfaces on core plugins #302
  3. Plugin infrastructure (attachContext + PluginContext) — feat(appkit): plugin infrastructure — attachContext + PluginContext mediator #303
  4. agents() plugin + createAgent(def) + markdown-driven agents — feat(appkit): agents() plugin, createAgent(def), and markdown-driven agents #304
  5. fromPlugin() DX + runAgent plugins arg + toolkit-resolver — feat(appkit): fromPlugin() DX, runAgent plugins arg, shared toolkit-resolver #305
  6. Reference app + dev-playground + docs — feat(appkit): reference agent-app, dev-playground chat UI, docs, and template #306

The v2 stack reorganizes the same work so no PR ships API that a later PR deletes. Start at #301 for the new entry point. Branches from this older stack are preserved unchanged.

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