add(coding-agent): add defineTool helper closes #2746

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

@@ -154,6 +154,7 @@ export type {
 } from "./types.js";
 // Type guards
 export {
+	defineTool,
 	isBashToolResult,
 	isEditToolResult,
 	isFindToolResult,

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

@@ -404,6 +404,21 @@ export interface ToolDefinition<TParams extends TSchema = TSchema, TDetails = un
 	) => Component;
 }
 
+type AnyToolDefinition = ToolDefinition<any, any, any>;
+
+/**
+ * Preserve parameter inference for standalone tool definitions.
+ *
+ * Use this when assigning a tool to a variable or passing it through arrays such
+ * as `customTools`, where contextual typing would otherwise widen params to
+ * `unknown`.
+ */
+export function defineTool<TParams extends TSchema, TDetails = unknown, TState = any>(
+	tool: ToolDefinition<TParams, TDetails, TState>,
+): ToolDefinition<TParams, TDetails, TState> & AnyToolDefinition {
+	return tool;
+}
+
 // ============================================================================
 // Resource Events
 // ============================================================================

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

@@ -28,6 +28,7 @@ export {
 	type AgentToolUpdateCallback,
 	type BeforeAgentStartEvent,
 	type ContextEvent,
+	defineTool,
 	discoverAndLoadExtensions,
 	type ExecOptions,
 	type ExecResult,