From fbd8aecaa1c7a3337db562adb549d5aa35848d23 Mon Sep 17 00:00:00 2001
From: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>
Date: Thu, 29 Oct 2026 23:13:02 -0500
Subject: [PATCH] fix(ai): keep tools with a throwing execute runnable (#60431)

---
 packages/ai/src/index.ts             |  5 +++--
 packages/ai/src/tool.ts              | 22 +++++++++++++++-------
 packages/ai/test/loop-tools.types.ts |  8 ++++++++
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/packages/ai/src/index.ts b/packages/ai/src/index.ts
index d1adf6f1f8c..abf396eb328 100644
--- a/packages/ai/src/index.ts
+++ b/packages/ai/src/index.ts
@@ -35,7 +35,8 @@ import {
   type TranscriptionRequest,
   type TranscriptionRequestInput,
 } from "./transcription.js"
-import { ToolFailure, build, type ToolExecuteContext, type ToolOptions, type ToolSchema } from "./tool.js"
+import { ToolFailure, build } from "./tool.js"
+import type { NoExecute, ToolExecuteContext, ToolOptions, ToolSchema } from "./tool.js"
 import { fileMediaType } from "./utils/media-type.js"
 import { Video, type VideoModel, type VideoRequest, type VideoRequestInput } from "./video.js"
 
@@ -282,7 +283,7 @@ const fileError = (message: string, cause: unknown) =>
 export const tool = <
   Parameters extends ToolSchema<any> = typeof Schema.Unknown,
   Success extends ToolSchema<any> = typeof Schema.Unknown,
-  Result extends Schema.Schema.Type<Success> | PromiseLike<Schema.Schema.Type<Success>> = never,
+  Result extends Schema.Schema.Type<Success> | PromiseLike<Schema.Schema.Type<Success>> | NoExecute = NoExecute,
 >(
   config: ToolOptions<
     Parameters,
diff --git a/packages/ai/src/tool.ts b/packages/ai/src/tool.ts
index 11f8f3dafa4..22e71ac65b3 100644
--- a/packages/ai/src/tool.ts
+++ b/packages/ai/src/tool.ts
@@ -130,7 +130,7 @@ export type ToolOptions<
 export const tool = <
   Parameters extends ToolSchema<any> = typeof Schema.Unknown,
   Success extends ToolSchema<any> = typeof Schema.Unknown,
-  Result extends Effect.Effect<Schema.Schema.Type<Success>, ToolFailure> = never,
+  Result extends Effect.Effect<Schema.Schema.Type<Success>, ToolFailure> | NoExecute = NoExecute,
 >(
   config: ToolOptions<
     Parameters,
@@ -139,14 +139,22 @@ export const tool = <
   >,
 ) => build(config, config.execute)
 
-/** @internal Builds a tool for both clients from its options and an Effect `execute`; no `execute` infers `never`. */
-export function build<Parameters extends ToolSchema<any>, Success extends ToolSchema<any>, Execute>(
-  config: ToolOptions<Parameters, Success, Execute>,
-  execute: ToolExecute<Parameters, ToolSchema<unknown>> | undefined,
-): Execute extends (...args: never) => never ? Tool<Parameters, Success> : ExecutableTool<Parameters, Success>
+declare const noExecute: unique symbol
+/** @internal The inferred `execute` result when `execute` is omitted; no function can return it. */
+export type NoExecute = { readonly [noExecute]: never }
+
+/** @internal Builds a tool for both clients from its options and an Effect `execute`. */
+export function build<Parameters extends ToolSchema<any>, Success extends ToolSchema<any>, Result>(
+  config: ToolOptions<Parameters, Success, (...args: never) => Result>,
+  execute: ((params: Schema.Schema.Type<Parameters>, context?: ToolExecuteContext) => unknown) | undefined,
+): 0 extends 1 & Result // `any`
+  ? ExecutableTool<Parameters, Success>
+  : [Result, NoExecute] extends [NoExecute, Result]
+    ? Tool<Parameters, Success>
+    : ExecutableTool<Parameters, Success>
 export function build(
   config: ToolOptions<ToolSchema<any>, ToolSchema<any>, unknown>,
-  execute: ToolExecute<ToolSchema<any>, ToolSchema<any>> | undefined,
+  execute: ((params: any, context?: ToolExecuteContext) => any) | undefined,
 ): Tool {
   const shared = {
     description: config.description,
diff --git a/packages/ai/test/loop-tools.types.ts b/packages/ai/test/loop-tools.types.ts
index 7c6b059e549..dce970821b6 100644
--- a/packages/ai/test/loop-tools.types.ts
+++ b/packages/ai/test/loop-tools.types.ts
@@ -47,3 +47,11 @@ LLM.loop({ model, prompt: "Use any tool.", tools: { add, echo, weather, shout }
 
 // @ts-expect-error The loop runs tools, so each one needs an execute handler.
 LLM.loop({ model, prompt: "Get weather.", tools: { schemaOnly } })
+
+const unavailable = () => {
+  throw new Error("Unavailable.")
+}
+const fail = AI.tool({ description: "Fail.", parameters: Schema.String, execute: unavailable })
+const parse = AI.tool({ description: "Parse.", parameters: Schema.String, execute: (text) => JSON.parse(text) })
+const inspect = tool({ description: "Inspect.", parameters: Schema.String, execute: () => Effect.succeed<unknown>(1) })
+ai.llm.loop({ model, prompt: "Fail.", tools: { fail, parse, inspect } })