feat(appkit): shared agent types and Databricks adapter

Foundation layer for the agents feature. Adds the portable type surface
that every downstream layer builds on, plus the Databricks Model Serving
adapter so the agents plugin (later PR) can target workspace-hosted
models.

### Shared agent types

`packages/shared/src/agent.ts` — no behavior, just the type vocabulary:
`AgentAdapter`, `AgentEvent`, `AgentInput`, `AgentRunContext`,
`AgentToolDefinition`, `Message`, `Thread`, `ThreadStore`,
`ToolAnnotations`, `ToolCall`, `ToolProvider`, `ResponseStreamEvent`.
Exported from the shared barrel.

### Adapter

`packages/appkit/src/agents/databricks.ts` — `DatabricksAdapter`:
streams OpenAI-compatible completions against a Databricks Model
Serving endpoint (raw fetch + SSE, no vendor SDKs). Also ships
`createDatabricksModel`, a Vercel-AI-SDK helper that returns a model
object you can pass to `streamText`/`useChat`/etc. — handles URL
rewriting (`/chat/completions` -> `/invocations`), per-request auth
refresh, and tool-name sanitization.

`@ai-sdk/openai` is a devDependency consumed by `createDatabricksModel`
via dynamic `import()`; consumers who use that helper install it
alongside `@databricks/appkit`.

Author: MarioCadenas

knip.json

@@ -7,7 +7,6 @@
     "docs"
   ],
   "workspaces": {
-    "packages/appkit": {},
     "packages/appkit-ui": {
       "ignoreDependencies": ["tailwindcss", "tw-animate-css"]
     }
@@ -17,6 +16,11 @@
     "**/*.example.tsx",
     "**/*.css",
     "packages/appkit/src/plugins/vector-search/**",
+    "packages/appkit/src/plugin/index.ts",
+    "packages/appkit/src/plugins/agents/index.ts",
+    "packages/appkit/src/plugins/agents/tools/index.ts",
+    "packages/appkit/src/plugins/agents/from-plugin.ts",
+    "packages/appkit/src/plugins/agents/load-agents.ts",
     "template/**",
     "tools/**",
     "docs/**"

packages/appkit/package.json

@@ -29,6 +29,10 @@
       "development": "./src/index.ts",
       "default": "./dist/index.js"
     },
+    "./agents/databricks": {
+      "development": "./src/agents/databricks.ts",
+      "default": "./dist/agents/databricks.js"
+    },
     "./type-generator": {
       "types": "./dist/type-generator/index.d.ts",
       "development": "./src/type-generator/index.ts",
@@ -93,6 +97,7 @@
   "publishConfig": {
     "exports": {
       ".": "./dist/index.js",
+      "./agents/databricks": "./dist/agents/databricks.js",
       "./dist/shared/src/plugin": "./dist/shared/src/plugin.d.ts",
       "./type-generator": "./dist/type-generator/index.js",
       "./package.json": "./package.json"