fix: extension loading in Bun binary (#681)

- Remove loader exports from index.ts to break circular dependency
- Static import of index.js in loader.ts for virtualModules
- Add @mariozechner/pi-agent-core to virtualModules
- Update @mariozechner/jiti to 2.6.5 (bundles babel for Bun binary)
- Update SDK docs to use correct extension terminology

packages/coding-agent/docs/sdk.md

@@ -735,12 +735,12 @@ import {
   discoverAuthStorage,
   discoverModels,
   discoverSkills,
-  discoverHooks,
-  discoverCustomTools,
+  discoverExtensions,
   discoverContextFiles,
   discoverPromptTemplates,
   loadSettings,
   buildSystemPrompt,
+  createEventBus,
 } from "@mariozechner/pi-coding-agent";
 
 // Auth and Models
@@ -754,19 +754,16 @@ const builtIn = getModel("anthropic", "claude-opus-4-5"); // Built-in only
 // Skills
 const { skills, warnings } = discoverSkills(cwd, agentDir, skillsSettings);
 
-// Hooks (async - loads TypeScript)
-// Pass eventBus to share pi.events across hooks/tools
+// Extensions (async - loads TypeScript)
+// Pass eventBus to share pi.events across extensions
 const eventBus = createEventBus();
-const hooks = await discoverHooks(eventBus, cwd, agentDir);
-
-// Custom tools (async - loads TypeScript)
-const tools = await discoverCustomTools(eventBus, cwd, agentDir);
+const { extensions, errors } = await discoverExtensions(eventBus, cwd, agentDir);
 
 // Context files
 const contextFiles = discoverContextFiles(cwd, agentDir);
 
 // Prompt templates
-const commands = discoverPromptTemplates(cwd, agentDir);
+const templates = discoverPromptTemplates(cwd, agentDir);
 
 // Settings (global + project merged)
 const settings = loadSettings(cwd, agentDir);
@@ -816,8 +813,8 @@ import {
   SettingsManager,
   readTool,
   bashTool,
-  type HookFactory,
-  type CustomTool,
+  type ExtensionFactory,
+  type ToolDefinition,
 } from "@mariozechner/pi-coding-agent";
 
 // Set up auth storage (custom location)
@@ -831,16 +828,16 @@ if (process.env.MY_KEY) {
 // Model registry (no custom models.json)
 const modelRegistry = new ModelRegistry(authStorage);
 
-// Inline hook
-const auditHook: HookFactory = (api) => {
-  api.on("tool_call", async (event) => {
+// Inline extension
+const auditExtension: ExtensionFactory = (pi) => {
+  pi.on("tool_call", async (event) => {
     console.log(`[Audit] ${event.toolName}`);
     return undefined;
   });
 };
 
 // Inline tool
-const statusTool: CustomTool = {
+const statusTool: ToolDefinition = {
   name: "status",
   label: "Status",
   description: "Get system status",
@@ -872,8 +869,8 @@ const { session } = await createAgentSession({
   systemPrompt: "You are a minimal assistant. Be concise.",
   
   tools: [readTool, bashTool],
-  customTools: [{ tool: statusTool }],
-  hooks: [{ factory: auditHook }],
+  customTools: [statusTool],
+  extensions: [auditExtension],
   skills: [],
   contextFiles: [],
   promptTemplates: [],
@@ -961,7 +958,7 @@ The SDK is preferred when:
 - You want type safety
 - You're in the same Node.js process
 - You need direct access to agent state
-- You want to customize tools/hooks programmatically
+- You want to customize tools/extensions programmatically
 
 RPC mode is preferred when:
 - You're integrating from another language
@@ -984,12 +981,11 @@ discoverModels
 
 // Discovery
 discoverSkills
-discoverHooks
-discoverCustomTools
+discoverExtensions
 discoverContextFiles
 discoverPromptTemplates
 
-// Event Bus (for shared hook/tool communication)
+// Event Bus (for shared extension communication)
 createEventBus
 
 // Helpers
@@ -1015,8 +1011,9 @@ createGrepTool, createFindTool, createLsTool
 // Types
 type CreateAgentSessionOptions
 type CreateAgentSessionResult
-type CustomTool
-type HookFactory
+type ExtensionFactory
+type ExtensionAPI
+type ToolDefinition
 type Skill
 type PromptTemplate
 type Settings
@@ -1024,28 +1021,4 @@ type SkillsSettings
 type Tool
 ```
 
-For hook types, import from the hooks subpath:
-
-```typescript
-import type {
-  HookAPI,
-  HookMessage,
-  HookFactory,
-  HookEventContext,
-  HookCommandContext,
-  ToolCallEvent,
-  ToolResultEvent,
-} from "@mariozechner/pi-coding-agent/hooks";
-```
-
-For message utilities:
-
-```typescript
-import { isHookMessage, createHookMessage } from "@mariozechner/pi-coding-agent";
-```
-
-For config utilities:
-
-```typescript
-import { getAgentDir } from "@mariozechner/pi-coding-agent/config";
-```
+For extension types, see [extensions.md](extensions.md) for the full API.