feat: inject available agents into system prompt

src/app/api/chat/actions.ts

@@ -33,7 +33,7 @@ import logger from "logger";
 import { JSONSchema7 } from "json-schema";
 import { ObjectJsonSchema7 } from "app-types/util";
 import { jsonSchemaToZod } from "lib/json-schema-to-zod";
-import { Agent } from "app-types/agent";
+import { Agent, AgentSummary } from "app-types/agent";
 
 export async function getUserId() {
   const session = await getSession();
@@ -226,6 +226,16 @@ export async function rememberAgentAction(
   return cachedAgent as Agent | undefined;
 }
 
+export async function rememberAvailableAgentsAction(userId: string) {
+  const key = CacheKeys.availableAgents(userId);
+  let cachedAgents = await serverCache.get<AgentSummary[] | null>(key);
+  if (!cachedAgents) {
+    cachedAgents = await agentRepository.selectAgents(userId, ["all"], 50);
+    await serverCache.set(key, cachedAgents, 1000 * 60 * 5); // 5 minutes cache
+  }
+  return cachedAgents ?? [];
+}
+
 export async function exportChatAction({
   threadId,
   expiresAt,

src/app/api/chat/route.ts

@@ -42,6 +42,7 @@ import {
 } from "./shared.chat";
 import {
   rememberAgentAction,
+  rememberAvailableAgentsAction,
   rememberMcpServerCustomizationsAction,
 } from "./actions";
 import { getSession } from "auth/server";
@@ -269,8 +270,18 @@ export async function POST(request: Request) {
           .map((v) => filterMcpServerCustomizations(MCP_TOOLS!, v))
           .orElse({});
 
+        // Fetch available agents only when no agent is selected
+        const availableAgents = !agent
+          ? await rememberAvailableAgentsAction(session.user.id)
+          : undefined;
+
         const systemPrompt = mergeSystemPrompt(
-          buildUserSystemPrompt(session.user, userPreferences, agent),
+          buildUserSystemPrompt(
+            session.user,
+            userPreferences,
+            agent,
+            availableAgents,
+          ),
           buildMcpServerCustomizationsSystemPrompt(mcpServerCustomizations),
           !supportToolCall && buildToolCallUnsupportedModelSystemPrompt,
         );

src/lib/ai/prompts.test.ts

@@ -0,0 +1,122 @@
+import { describe, expect, it } from "vitest";
+import { buildUserSystemPrompt } from "./prompts";
+import { AgentSummary, Agent } from "app-types/agent";
+
+describe("buildUserSystemPrompt", () => {
+  const mockAvailableAgents: AgentSummary[] = [
+    {
+      id: "agent-1",
+      name: "Code Reviewer",
+      description: "Reviews code for best practices",
+      userId: "user-1",
+      visibility: "private",
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    },
+    {
+      id: "agent-2",
+      name: "Technical Writer",
+      description: "Writes documentation",
+      userId: "user-1",
+      visibility: "public",
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    },
+    {
+      id: "agent-3",
+      name: "Simple Agent",
+      // No description
+      userId: "user-1",
+      visibility: "private",
+      createdAt: new Date(),
+      updatedAt: new Date(),
+    },
+  ];
+
+  const mockSelectedAgent: Agent = {
+    id: "selected-agent",
+    name: "Selected Agent",
+    description: "The currently selected agent",
+    userId: "user-1",
+    visibility: "private",
+    createdAt: new Date(),
+    updatedAt: new Date(),
+    instructions: {
+      role: "Testing Expert",
+      systemPrompt: "You are a testing expert.",
+    },
+  };
+
+  describe("available agents section", () => {
+    it("should include available agents when no agent is selected", () => {
+      const prompt = buildUserSystemPrompt(
+        undefined,
+        undefined,
+        undefined,
+        mockAvailableAgents,
+      );
+
+      expect(prompt).toContain("<available_agents>");
+      expect(prompt).toContain("</available_agents>");
+      expect(prompt).toContain(
+        "**Code Reviewer**: Reviews code for best practices",
+      );
+      expect(prompt).toContain("**Technical Writer**: Writes documentation");
+      expect(prompt).toContain("**Simple Agent**");
+      expect(prompt).toContain("typing @ followed by the agent name");
+      expect(prompt).toContain("from the tools menu");
+      expect(prompt).toContain("agents menu in the sidebar");
+    });
+
+    it("should not include available agents section when an agent is selected", () => {
+      const prompt = buildUserSystemPrompt(
+        undefined,
+        undefined,
+        mockSelectedAgent,
+        mockAvailableAgents,
+      );
+
+      expect(prompt).not.toContain("<available_agents>");
+      expect(prompt).not.toContain("</available_agents>");
+      // Should include the selected agent's instructions instead
+      expect(prompt).toContain("Selected Agent");
+      expect(prompt).toContain("Testing Expert");
+    });
+
+    it("should not include available agents section when list is empty", () => {
+      const prompt = buildUserSystemPrompt(undefined, undefined, undefined, []);
+
+      expect(prompt).not.toContain("<available_agents>");
+      expect(prompt).not.toContain("</available_agents>");
+    });
+
+    it("should not include available agents section when list is undefined", () => {
+      const prompt = buildUserSystemPrompt(
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+      );
+
+      expect(prompt).not.toContain("<available_agents>");
+      expect(prompt).not.toContain("</available_agents>");
+    });
+
+    it("should handle agents without descriptions", () => {
+      const prompt = buildUserSystemPrompt(undefined, undefined, undefined, [
+        {
+          id: "no-desc",
+          name: "No Description Agent",
+          userId: "user-1",
+          visibility: "private",
+          createdAt: new Date(),
+          updatedAt: new Date(),
+        },
+      ]);
+
+      expect(prompt).toContain("**No Description Agent**");
+      // Should not have a colon after the name when no description
+      expect(prompt).not.toContain("**No Description Agent**:");
+    });
+  });
+});

src/lib/ai/prompts.ts

@@ -4,7 +4,7 @@ import { UserPreferences } from "app-types/user";
 import { User } from "better-auth";
 import { createMCPToolId } from "./mcp/mcp-tool-id";
 import { format } from "date-fns";
-import { Agent } from "app-types/agent";
+import { Agent, AgentSummary } from "app-types/agent";
 
 export const CREATE_THREAD_TITLE_PROMPT = `
 You are a chat title generation expert.
@@ -52,6 +52,7 @@ export const buildUserSystemPrompt = (
   user?: User,
   userPreferences?: UserPreferences,
   agent?: Agent,
+  availableAgents?: AgentSummary[],
 ) => {
   const assistantName =
     agent?.name || userPreferences?.botName || "better-chatbot";
@@ -99,6 +100,25 @@ You can assist with:
 - Adapting communication to user preferences and context
 </general_capabilities>`;
 
+  // Available agents section (only when no agent is selected)
+  if (!agent && availableAgents && availableAgents.length > 0) {
+    const agentsList = availableAgents
+      .map((a) => {
+        const desc = a.description ? `: ${a.description}` : "";
+        return `- **${a.name}**${desc}`;
+      })
+      .join("\n");
+
+    prompt += `
+
+<available_agents>
+The user has access to the following specialized agents:
+${agentsList}
+
+If the user's request would benefit from a specialized agent's expertise, you may suggest they select one. Users can select an agent by typing @ followed by the agent name, from the tools menu, or from the agents menu in the sidebar. Only suggest an agent if it's clearly relevant to what they're asking about.
+</available_agents>`;
+  }
+
   // Communication preferences
   const displayName = userPreferences?.displayName || user?.name;
   const hasStyleExample = userPreferences?.responseStyleExample;

src/lib/cache/cache-keys.ts

@@ -4,4 +4,5 @@ export const CacheKeys = {
   mcpServerCustomizations: (userId: string) =>
     `mcp-server-customizations-${userId}`,
   agentInstructions: (agent: string) => `agent-instructions-${agent}`,
+  availableAgents: (userId: string) => `available-agents-${userId}`,
 };