feat: add provider availability check before creating sessions

packages/server/src/server/agent/agent-manager.ts

@@ -340,6 +340,10 @@ export class AgentManager {
       agentId: resolvedAgentId,
     });
     const client = this.requireClient(normalizedConfig.provider);
+    const available = await client.isAvailable();
+    if (!available) {
+      throw new Error(`Provider '${normalizedConfig.provider}' is not available. Please ensure the CLI is installed.`);
+    }
     const session = await client.createSession(normalizedConfig);
     return this.registerSession(
       session,

packages/server/src/server/agent/agent-sdk-types.ts

@@ -287,4 +287,9 @@ export interface AgentClient {
   resumeSession(handle: AgentPersistenceHandle, overrides?: Partial<AgentSessionConfig>): Promise<AgentSession>;
   listModels(options?: ListModelsOptions): Promise<AgentModelDefinition[]>;
   listPersistedAgents?(options?: ListPersistedAgentsOptions): Promise<PersistedAgentDescriptor[]>;
+  /**
+   * Check if this provider is available (CLI binary is installed).
+   * Returns true if available, false otherwise.
+   */
+  isAvailable(): Promise<boolean>;
 }

packages/server/src/server/agent/providers/claude-agent.ts

@@ -1,3 +1,4 @@
+import { execSync } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import fs from "node:fs";
 import { promises } from "node:fs";
@@ -403,6 +404,15 @@ export class ClaudeAgentClient implements AgentClient {
     return descriptors;
   }
 
+  async isAvailable(): Promise<boolean> {
+    try {
+      const claudePath = execSync("which claude", { encoding: "utf8" }).trim();
+      return Boolean(claudePath);
+    } catch {
+      return false;
+    }
+  }
+
   private assertConfig(config: AgentSessionConfig): ClaudeAgentConfig {
     if (config.provider !== "claude") {
       throw new Error(`ClaudeAgentClient received config for provider '${config.provider}'`);

packages/server/src/server/agent/providers/codex-app-server-agent.ts

@@ -1729,4 +1729,13 @@ export class CodexAppServerAgentClient implements AgentClient {
       await client.dispose();
     }
   }
+
+  async isAvailable(): Promise<boolean> {
+    try {
+      const codexPath = execSync("which codex", { encoding: "utf8" }).trim();
+      return Boolean(codexPath);
+    } catch {
+      return false;
+    }
+  }
 }

packages/server/src/server/agent/providers/codex-mcp-agent.ts

@@ -4800,6 +4800,15 @@ export class CodexMcpAgentClient implements AgentClient {
       await client.dispose();
     }
   }
+
+  async isAvailable(): Promise<boolean> {
+    try {
+      const codexPath = execSync("which codex", { encoding: "utf8" }).trim();
+      return Boolean(codexPath);
+    } catch {
+      return false;
+    }
+  }
 }
 
 export const __test__ = {

packages/server/src/server/agent/providers/opencode-agent.ts

@@ -1,4 +1,4 @@
-import { spawn, type ChildProcess } from "node:child_process";
+import { execSync, spawn, type ChildProcess } from "node:child_process";
 import { createOpencodeClient, type OpencodeClient } from "@opencode-ai/sdk/v2/client";
 import net from "node:net";
 import type { Logger } from "pino";
@@ -318,6 +318,15 @@ export class OpenCodeAgentClient implements AgentClient {
     return [];
   }
 
+  async isAvailable(): Promise<boolean> {
+    try {
+      const opencodePath = execSync("which opencode", { encoding: "utf8" }).trim();
+      return Boolean(opencodePath);
+    } catch {
+      return false;
+    }
+  }
+
   private assertConfig(config: AgentSessionConfig): OpenCodeAgentConfig {
     if (config.provider !== "opencode") {
       throw new Error(`OpenCodeAgentClient received config for provider '${config.provider}'`);

packages/server/src/server/test-utils/fake-agent-client.ts

@@ -664,6 +664,10 @@ class FakeAgentClient implements AgentClient {
       { provider: this.provider, id: "test-model", label: "Test Model", isDefault: true },
     ];
   }
+
+  async isAvailable(): Promise<boolean> {
+    return true;
+  }
 }
 
 export function createTestAgentClients(): Record<string, AgentClient> {