fix: fail faster when mcp servers fail to connect

Author: damassi

src/components/UserInput.tsx

@@ -46,7 +46,7 @@ export const UserInput: React.FC = () => {
 
   return (
     <Box>
-      <BlinkCaret />
+      <BlinkCaret enabled={!store.isProcessing} />
 
       <TextInput
         value={store.input}

src/hooks/useAgent.ts

@@ -6,11 +6,12 @@ import { messageTypes, runAgentLoop } from "utils/runAgentLoop"
 export function useAgent() {
   const messageQueue = AgentStore.useStoreState((state) => state.messageQueue)
   const config = AgentStore.useStoreState((state) => state.config)
+  const mcpServers = AgentStore.useStoreState((state) => state.mcpServers)
   const actions = AgentStore.useStoreActions((actions) => actions)
   const currentAssistantMessageRef = useRef("")
   const sessionIdRef = useRef<string | undefined>(undefined)
   const abortControllerRef = useRef<AbortController | undefined>(undefined)
-  const connectedServersRef = useRef<Set<string>>(new Set())
+  const inferredServersRef = useRef<Set<string>>(new Set())
 
   const runQuery = useCallback(
     async (userMessage: string) => {
@@ -32,7 +33,8 @@ export function useAgent() {
         const agentLoop = runAgentLoop({
           abortController,
           config,
-          connectedServers: connectedServersRef.current,
+          inferredServers: inferredServersRef.current,
+          mcpServers,
           messageQueue,
           onToolPermissionRequest: (toolName, input) => {
             actions.setPendingToolPermission({ toolName, input })

src/mcp/getAgentStatus.ts

@@ -7,12 +7,12 @@ export const getAgentStatus = async (mcpServer?: McpServer) => {
   const config = await loadConfig()
   const messageQueue = new MessageQueue()
   const abortController = new AbortController()
-  const connectedServers = new Set<string>()
+  const inferredServers = new Set<string>()
 
   const agentLoop = runAgentLoop({
     abortController,
     config,
-    connectedServers,
+    inferredServers,
     messageQueue,
     userMessage: "status",
   })

src/mcp/getMcpServer.ts

@@ -1,4 +1,5 @@
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"
+import type { McpServerStatus } from "store"
 import { registerAskAgentTool } from "mcp/tools/askAgent"
 import { registerAskAgentSlackbotTool } from "mcp/tools/askAgentSlackbot"
 import { registerGetAgentStatusTool } from "mcp/tools/getAgentStatus"
@@ -10,8 +11,11 @@ export const getMcpServer = () => {
   // Map thread IDs to Claude Agent SDK session IDs for per-thread isolation
   const threadSessions = new Map<string, string>()
 
-  // Map session IDs to connected MCP servers for persistence across requests
-  const sessionConnectedServers = new Map<string, Set<string>>()
+  // Map session IDs to inferred MCP servers for persistence across requests
+  const sessionInferredServers = new Map<string, Set<string>>()
+
+  // Map session IDs to MCP server statuses for persistence across requests
+  const sessionMcpServers = new Map<string, McpServerStatus[]>()
 
   const mcpServer = new McpServer(
     {
@@ -32,7 +36,8 @@ export const getMcpServer = () => {
       get sessionId() {
         return sessionId
       },
-      sessionConnectedServers,
+      sessionInferredServers,
+      sessionMcpServers,
       onSessionIdUpdate: (newSessionId) => {
         sessionId = newSessionId
       },
@@ -43,7 +48,8 @@ export const getMcpServer = () => {
     mcpServer,
     context: {
       threadSessions,
-      sessionConnectedServers,
+      sessionInferredServers,
+      sessionMcpServers,
     },
   })
 

src/mcp/runStandaloneAgentLoop.ts

@@ -1,12 +1,14 @@
 import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"
+import type { McpServerStatus } from "store"
 import { loadConfig } from "utils/loadConfig"
 import { log } from "utils/logger"
 import { MessageQueue } from "utils/MessageQueue"
 import { contentTypes, messageTypes, runAgentLoop } from "utils/runAgentLoop"
 
 interface RunQueryOptions {
   additionalSystemPrompt?: string
-  existingConnectedServers?: Set<string>
+  existingInferredServers?: Set<string>
+  existingMcpServers?: McpServerStatus[]
   mcpServer: McpServer
   onSessionIdReceived?: (sessionId: string) => void
   prompt: string
@@ -15,7 +17,8 @@ interface RunQueryOptions {
 
 export const runStandaloneAgentLoop = async ({
   additionalSystemPrompt,
-  existingConnectedServers,
+  existingInferredServers,
+  existingMcpServers,
   mcpServer,
   onSessionIdReceived,
   prompt,
@@ -25,17 +28,16 @@ export const runStandaloneAgentLoop = async ({
   const messageQueue = new MessageQueue()
   const streamEnabled = config.stream ?? false
 
-  const connectedServers = existingConnectedServers ?? new Set<string>()
+  const inferredServers = existingInferredServers ?? new Set<string>()
   const abortController = new AbortController()
 
   const agentLoop = runAgentLoop({
     abortController,
     additionalSystemPrompt,
     config,
-    connectedServers,
+    inferredServers,
+    mcpServers: existingMcpServers,
     messageQueue,
-    sessionId,
-    userMessage: prompt,
     onServerConnection: async (status) => {
       await mcpServer.sendLoggingMessage({
         level: "info",
@@ -45,6 +47,8 @@ export const runStandaloneAgentLoop = async ({
         }),
       })
     },
+    sessionId,
+    userMessage: prompt,
   })
 
   let finalResponse = ""
@@ -155,7 +159,7 @@ export const runStandaloneAgentLoop = async ({
 
           return {
             response: finalResponse,
-            connectedServers,
+            inferredServers,
           }
         }
       }
@@ -166,6 +170,6 @@ export const runStandaloneAgentLoop = async ({
 
   return {
     response: finalResponse,
-    connectedServers,
+    inferredServers,
   }
 }

src/mcp/tools/askAgent.ts

@@ -1,10 +1,12 @@
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"
+import type { McpServerStatus } from "store"
 import { runStandaloneAgentLoop } from "mcp/runStandaloneAgentLoop"
 import { z } from "zod"
 
 export interface AskAgentContext {
   sessionId?: string
-  sessionConnectedServers: Map<string, Set<string>>
+  sessionInferredServers: Map<string, Set<string>>
+  sessionMcpServers: Map<string, McpServerStatus[]>
   onSessionIdUpdate: (sessionId: string) => void
 }
 
@@ -27,23 +29,28 @@ export const registerAskAgentTool = ({
       },
     },
     async ({ query }) => {
-      const existingConnectedServers = context.sessionId
-        ? context.sessionConnectedServers.get(context.sessionId)
+      const existingInferredServers = context.sessionId
+        ? context.sessionInferredServers.get(context.sessionId)
         : undefined
 
-      const { response, connectedServers } = await runStandaloneAgentLoop({
+      const existingMcpServers = context.sessionId
+        ? context.sessionMcpServers.get(context.sessionId)
+        : undefined
+
+      const { response, inferredServers } = await runStandaloneAgentLoop({
         prompt: query,
         mcpServer,
         sessionId: context.sessionId,
-        existingConnectedServers,
+        existingInferredServers,
+        existingMcpServers,
         onSessionIdReceived: (newSessionId) => {
           context.onSessionIdUpdate(newSessionId)
         },
       })
 
-      // Update the session's connected servers
+      // Update the session's inferred servers
       if (context.sessionId) {
-        context.sessionConnectedServers.set(context.sessionId, connectedServers)
+        context.sessionInferredServers.set(context.sessionId, inferredServers)
       }
 
       return {

src/mcp/tools/askAgentSlackbot.ts

@@ -1,10 +1,12 @@
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"
+import type { McpServerStatus } from "store"
 import { runStandaloneAgentLoop } from "mcp/runStandaloneAgentLoop"
 import { z } from "zod"
 
 export interface AskAgentSlackbotContext {
   threadSessions: Map<string, string>
-  sessionConnectedServers: Map<string, Set<string>>
+  sessionInferredServers: Map<string, Set<string>>
+  sessionMcpServers: Map<string, McpServerStatus[]>
 }
 
 export interface RegisterAskAgentSlackbotToolProps {
@@ -41,29 +43,34 @@ export const registerAskAgentSlackbotTool = ({
         ? context.threadSessions.get(threadId)
         : undefined
 
-      const existingConnectedServers = existingSessionId
-        ? context.sessionConnectedServers.get(existingSessionId)
+      const existingInferredServers = existingSessionId
+        ? context.sessionInferredServers.get(existingSessionId)
         : undefined
 
-      const { response, connectedServers } = await runStandaloneAgentLoop({
+      const existingMcpServers = existingSessionId
+        ? context.sessionMcpServers.get(existingSessionId)
+        : undefined
+
+      const { response, inferredServers } = await runStandaloneAgentLoop({
         prompt: query,
         mcpServer,
         sessionId: existingSessionId,
         additionalSystemPrompt: systemPrompt,
-        existingConnectedServers,
+        existingInferredServers,
+        existingMcpServers,
         onSessionIdReceived: (newSessionId) => {
           if (threadId) {
             context.threadSessions.set(threadId, newSessionId)
           }
         },
       })
 
-      // Update the session's connected servers
+      // Update the session's inferred servers
       if (existingSessionId || threadId) {
         const sessionId =
           existingSessionId || context.threadSessions.get(threadId!)
         if (sessionId) {
-          context.sessionConnectedServers.set(sessionId, connectedServers)
+          context.sessionInferredServers.set(sessionId, inferredServers)
         }
       }
 

src/utils/__tests__/getPrompt.test.ts

@@ -145,47 +145,80 @@ describe("buildSystemPrompt", () => {
     expect(prompt).toContain("GitHub instructions")
   })
 
-  test("should include connected MCP servers in system prompt", async () => {
+  test("should include inferred MCP servers in system prompt", async () => {
     const config: AgentChatConfig = {
       mcpServers: {},
     }
-    const connectedServers = new Set(["github", "gitlab"])
+    const inferredServers = new Set(["github", "gitlab"])
 
     const prompt = await buildSystemPrompt({
       config,
-      connectedServers,
+      inferredServers,
     })
 
-    expect(prompt).toContain("Connected MCP Servers")
+    expect(prompt).toContain("Server Selection Context")
     expect(prompt).toContain("github, gitlab")
   })
 
-  test("should handle empty connected servers set", async () => {
+  test("should include connected and failed MCP servers sections", async () => {
     const config: AgentChatConfig = {
       mcpServers: {},
     }
-    const connectedServers = new Set<string>()
+    const mcpServers = [
+      { name: "github", status: "connected" },
+      { name: "gitlab", status: "failed" },
+    ]
 
     const prompt = await buildSystemPrompt({
       config,
-      connectedServers,
+      mcpServers,
     })
 
-    expect(prompt).toContain("Connected MCP Servers")
-    expect(prompt).toContain(
-      "The following MCP servers are currently connected and available:"
-    )
+    expect(prompt).toContain("Available MCP Servers")
+    expect(prompt).toContain("- github")
+    expect(prompt).toContain("ONLY servers with available tools")
+    expect(prompt).toContain("Unavailable MCP Servers")
+    expect(prompt).toContain("- gitlab")
+    expect(prompt).toContain("These servers have NO tools available")
   })
 
-  test("should work without connectedServers parameter", async () => {
+  test("should not include connection status sections when no mcpServers provided", async () => {
+    const config: AgentChatConfig = {
+      mcpServers: {},
+    }
+
+    const prompt = await buildSystemPrompt({
+      config,
+    })
+
+    expect(prompt).not.toContain("Available MCP Servers")
+    expect(prompt).not.toContain("Unavailable MCP Servers")
+  })
+
+  test("should handle empty inferred servers set", async () => {
+    const config: AgentChatConfig = {
+      mcpServers: {},
+    }
+    const inferredServers = new Set<string>()
+
+    const prompt = await buildSystemPrompt({
+      config,
+      inferredServers,
+    })
+
+    expect(prompt).toContain("Current date:")
+    expect(prompt).not.toContain("Server Selection Context")
+  })
+
+  test("should work without inferredServers parameter", async () => {
     const config: AgentChatConfig = {
       mcpServers: {},
     }
 
     const prompt = await buildSystemPrompt({ config })
 
-    expect(prompt).toContain("Connected MCP Servers")
     expect(prompt).toContain("Current date:")
+    expect(prompt).not.toContain("Server Selection Context")
   })
 
   test("should skip disabled MCP servers", async () => {