Add server-side validation for working directory existence

- Validate cwd exists before creating agent in session.ts
- Show error message when directory doesn't exist
- Add client-side warning display in new.tsx
- Block form submission for non-existent directories
- Add daemon e2e test for non-existent cwd validation
- Add createAgentExpectFail helper in daemon-client.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/server/src/server/daemon.e2e.test.ts

@@ -82,6 +82,19 @@ describe("daemon E2E", () => {
     expect(hasAssistantMessage).toBe(true);
   }, 180000); // 3 minute timeout for E2E test
 
+  test("fails to create agent with non-existent cwd", async () => {
+    const nonExistentCwd = "/this/path/does/not/exist/12345";
+
+    const result = await ctx.client.createAgentExpectFail({
+      provider: "codex",
+      cwd: nonExistentCwd,
+      title: "Should Fail Agent",
+    });
+
+    expect(result.error).toContain("Working directory does not exist");
+    expect(result.error).toContain(nonExistentCwd);
+  });
+
   describe("permission flow: Codex", () => {
     test(
       "approves permission and executes command",

packages/server/src/server/session.ts

@@ -1,5 +1,5 @@
 import { v4 as uuidv4 } from "uuid";
-import { readFile, mkdir, writeFile } from "fs/promises";
+import { readFile, mkdir, writeFile, stat } from "fs/promises";
 import { exec } from "child_process";
 import { promisify, inspect } from "util";
 import { join } from "path";
@@ -1273,6 +1273,24 @@ export class Session {
     );
 
     try {
+      // Validate that the working directory exists
+      const resolvedCwd = expandTilde(config.cwd);
+      try {
+        const stats = await stat(resolvedCwd);
+        if (!stats.isDirectory()) {
+          throw new Error(
+            `Working directory is not a directory: ${config.cwd}`
+          );
+        }
+      } catch (statError: any) {
+        if (statError.code === "ENOENT") {
+          throw new Error(
+            `Working directory does not exist: ${config.cwd}`
+          );
+        }
+        throw statError;
+      }
+
       const sessionConfig = await this.buildAgentSessionConfig(
         config,
         git,

packages/server/src/server/test-utils/daemon-client.ts

@@ -197,6 +197,50 @@ export class DaemonClient {
     ); // 60 second timeout for initialization
   }
 
+  /**
+   * Create an agent and expect it to fail.
+   * Returns the error message from the failure.
+   */
+  async createAgentExpectFail(
+    options: CreateAgentOptions
+  ): Promise<{ error: string }> {
+    const requestId = nanoid();
+
+    // Record the current queue position so we only check NEW messages
+    const startPosition = this.messageQueue.length;
+
+    this.send({
+      type: "create_agent_request",
+      requestId,
+      config: {
+        provider: options.provider,
+        cwd: options.cwd,
+        title: options.title,
+        model: options.model,
+        modeId: options.modeId,
+        mcpServers: options.mcpServers,
+        extra: options.extra,
+      },
+      initialPrompt: options.initialPrompt,
+    });
+
+    // Wait for either agent_create_failed status or timeout
+    return this.waitFor(
+      (msg) => {
+        if (
+          msg.type === "status" &&
+          msg.payload.status === "agent_create_failed" &&
+          msg.payload.requestId === requestId
+        ) {
+          return { error: String(msg.payload.error ?? "Unknown error") };
+        }
+        return null;
+      },
+      10000,
+      { skipQueueBefore: startPosition }
+    );
+  }
+
   async deleteAgent(agentId: string): Promise<void> {
     this.send({ type: "delete_agent_request", agentId });
     await this.waitFor((msg) => {