From e4bc8b765b6b96dfcf3c836c412e6f2916df0459 Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Fri, 28 Aug 2026 13:26:51 -0400
Subject: [PATCH] refactor(core): reuse MCP prompt helpers (#45660)

---
 packages/core/src/mcp/client.ts           | 21 +++------------
 packages/core/test/fixture/mcp-prompts.ts | 30 ++++++++++++++++++++++
 packages/core/test/mcp.test.ts            | 31 +++++++++++++++++++++++
 3 files changed, 64 insertions(+), 18 deletions(-)
 create mode 100644 packages/core/test/fixture/mcp-prompts.ts

diff --git a/packages/core/src/mcp/client.ts b/packages/core/src/mcp/client.ts
index 9f58e44b4c9..c0f2fc94cc7 100644
--- a/packages/core/src/mcp/client.ts
+++ b/packages/core/src/mcp/client.ts
@@ -10,17 +10,14 @@ import {
   CallToolResultSchema,
   ElicitationCompleteNotificationSchema,
   ElicitRequestSchema,
-  GetPromptResultSchema,
   type Implementation,
   type ElicitRequestFormParams,
   type ElicitRequestParams,
   type ElicitRequestURLParams,
   type ElicitResult,
-  ListPromptsResultSchema,
   ListRootsRequestSchema,
   ListToolsResultSchema,
   PromptListChangedNotificationSchema,
-  PromptSchema,
   ResourceListChangedNotificationSchema,
   type LoggingMessageNotification,
   LoggingMessageNotificationSchema,
@@ -41,10 +38,6 @@ const toError = (error: unknown) => (error instanceof Error ? error : new Error(
 const TolerantListToolsResult = ListToolsResultSchema.extend({
   tools: ToolSchema.omit({ outputSchema: true }).array(),
 })
-const TolerantListPromptsResult = ListPromptsResultSchema.extend({
-  prompts: PromptSchema.array(),
-})
-
 export class NeedsAuthError extends Schema.TaggedError<NeedsAuthError>()("MCP.NeedsAuthError", {
   server: Schema.String,
 }) {
@@ -301,12 +294,8 @@ export const connect = Effect.fnUntraced(function* (
           const prompts = yield* Effect.tryPromise({
             try: () =>
               paginate(
-                async (cursor) => {
-                  const params = cursor === undefined ? undefined : { cursor }
-                  return client.request({ method: "prompts/list", params }, TolerantListPromptsResult, {
-                    timeout: catalogTimeout,
-                  })
-                },
+                (cursor) =>
+                  client.listPrompts(cursor === undefined ? undefined : { cursor }, { timeout: catalogTimeout }),
                 (result) => result.prompts,
               ),
             catch: toError,
@@ -396,11 +385,7 @@ export const connect = Effect.fnUntraced(function* (
       prompt: (input) =>
         Effect.tryPromise({
           try: (signal) =>
-            client.request(
-              { method: "prompts/get", params: { name: input.name, arguments: input.args ?? {} } },
-              GetPromptResultSchema,
-              { signal, timeout: executionTimeout },
-            ),
+            client.getPrompt({ name: input.name, arguments: input.args ?? {} }, { signal, timeout: executionTimeout }),
           catch: toError,
         }).pipe(
           Effect.map((result) => ({
diff --git a/packages/core/test/fixture/mcp-prompts.ts b/packages/core/test/fixture/mcp-prompts.ts
new file mode 100644
index 00000000000..473b6f176cd
--- /dev/null
+++ b/packages/core/test/fixture/mcp-prompts.ts
@@ -0,0 +1,30 @@
+import { Server } from "@modelcontextprotocol/sdk/server/index.js"
+import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"
+import { GetPromptRequestSchema, ListPromptsRequestSchema } from "@modelcontextprotocol/sdk/types.js"
+
+const server = new Server({ name: "prompts", version: "1.0.0" }, { capabilities: { prompts: {} } })
+
+server.setRequestHandler(ListPromptsRequestSchema, ({ params }) =>
+  Promise.resolve(
+    params?.cursor === "page-2"
+      ? { prompts: [{ name: "second", description: "Second prompt" }] }
+      : {
+          prompts: [
+            {
+              name: "first",
+              description: "First prompt",
+              arguments: [{ name: "topic", description: "Topic to explain", required: true }],
+            },
+          ],
+          nextCursor: "page-2",
+        },
+  ),
+)
+
+server.setRequestHandler(GetPromptRequestSchema, ({ params }) =>
+  Promise.resolve({
+    messages: [{ role: "user", content: { type: "text", text: params.arguments?.topic ?? "missing" } }],
+  }),
+)
+
+await server.connect(new StdioServerTransport())
diff --git a/packages/core/test/mcp.test.ts b/packages/core/test/mcp.test.ts
index 959cc677473..79bcb36d0c0 100644
--- a/packages/core/test/mcp.test.ts
+++ b/packages/core/test/mcp.test.ts
@@ -474,6 +474,37 @@ test("retains output schemas across paginated MCP discovery", async () => {
   ])
 })
 
+test("lists paginated prompts and invokes them through the MCP client", async () => {
+  const result = await Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const connection = yield* connect(
+          "prompts",
+          new ConfigMCP.Local({
+            type: "local",
+            command: [process.execPath, path.join(import.meta.dir, "fixture/mcp-prompts.ts")],
+          }),
+          import.meta.dir,
+        )
+        return {
+          prompts: yield* connection.prompts(),
+          result: yield* connection.prompt({ name: "first", args: { topic: "Effect" } }),
+        }
+      }),
+    ),
+  )
+
+  expect(result.prompts).toEqual([
+    {
+      name: "first",
+      description: "First prompt",
+      arguments: [{ name: "topic", description: "Topic to explain", required: true }],
+    },
+    { name: "second", description: "Second prompt", arguments: undefined },
+  ])
+  expect(result.result).toEqual({ messages: [{ role: "user", content: { type: "text", text: "Effect" } }] })
+})
+
 test("spawns local MCP servers through the location environment", async () => {
   const spawns: Array<ChildProcess.Command> = []
   const cwd = path.join(import.meta.dir, "fixture")