Add type guards for tool_result event narrowing

- Export isBashToolResult, isReadToolResult, etc. type guards
- Update hooks.md with type guard usage examples
- Document custom tool handling in hooks.md

packages/coding-agent/src/core/hooks/index.ts

@@ -29,3 +29,12 @@ export type {
 	TurnStartEvent,
 	WriteToolResultEvent,
 } from "./types.js";
+export {
+	isBashToolResult,
+	isEditToolResult,
+	isFindToolResult,
+	isGrepToolResult,
+	isLsToolResult,
+	isReadToolResult,
+	isWriteToolResult,
+} from "./types.js";

packages/coding-agent/src/core/hooks/types.ts

@@ -224,6 +224,29 @@ export type ToolResultEvent =
 	| LsToolResultEvent
 	| CustomToolResultEvent;
 
+// Type guards for narrowing ToolResultEvent to specific tool types
+export function isBashToolResult(e: ToolResultEvent): e is BashToolResultEvent {
+	return e.toolName === "bash";
+}
+export function isReadToolResult(e: ToolResultEvent): e is ReadToolResultEvent {
+	return e.toolName === "read";
+}
+export function isEditToolResult(e: ToolResultEvent): e is EditToolResultEvent {
+	return e.toolName === "edit";
+}
+export function isWriteToolResult(e: ToolResultEvent): e is WriteToolResultEvent {
+	return e.toolName === "write";
+}
+export function isGrepToolResult(e: ToolResultEvent): e is GrepToolResultEvent {
+	return e.toolName === "grep";
+}
+export function isFindToolResult(e: ToolResultEvent): e is FindToolResultEvent {
+	return e.toolName === "find";
+}
+export function isLsToolResult(e: ToolResultEvent): e is LsToolResultEvent {
+	return e.toolName === "ls";
+}
+
 /**
  * Event data for branch event.
  */

packages/coding-agent/src/index.ts

@@ -35,7 +35,6 @@ export type {
 	ToolUIContext,
 } from "./core/custom-tools/index.js";
 export { discoverAndLoadCustomTools, loadCustomTools } from "./core/custom-tools/index.js";
-// Hook system types
 export type {
 	AgentEndEvent,
 	AgentStartEvent,
@@ -62,6 +61,16 @@ export type {
 	TurnStartEvent,
 	WriteToolResultEvent,
 } from "./core/hooks/index.js";
+// Hook system types and type guards
+export {
+	isBashToolResult,
+	isEditToolResult,
+	isFindToolResult,
+	isGrepToolResult,
+	isLsToolResult,
+	isReadToolResult,
+	isWriteToolResult,
+} from "./core/hooks/index.js";
 export { messageTransformer } from "./core/messages.js";
 export {
 	type CompactionEntry,