fix(new-agent): add path traversal containment check

Extracts validateAgentName() with path.resolve containment guard after
regex validation; returns clean ephemeral Discord reply on violation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/commands/new-agent.ts

@@ -12,6 +12,21 @@ import { setupAgentWorkspace } from "../agent/identity";
 // Allowed characters for agent names: lowercase letters, numbers, hyphens
 const NAME_PATTERN = /^[a-z0-9][a-z0-9-]{0,30}[a-z0-9]$/;
 
+/**
+ * Validates that an agent name is safe and does not escape the workspaces root
+ * via path traversal. Throws an Error if the resolved path would lie outside root.
+ */
+export function validateAgentName(name: string, workspacesRoot: string): void {
+  if (!name) {
+    throw new Error(`Ungültiger Agent-Name: "${name}"`);
+  }
+  const root = path.resolve(workspacesRoot);
+  const wsPath = path.resolve(root, name);
+  if (!wsPath.startsWith(root + path.sep)) {
+    throw new Error(`Ungültiger Agent-Name: "${name}"`);
+  }
+}
+
 export const newAgentCommand = new SlashCommandBuilder()
   .setName("new-agent")
   .setDescription("Erstellt einen neuen Agenten mit eigenem Kanal und Workspace")
@@ -48,6 +63,15 @@ export async function handleNewAgent(
     return;
   }
 
+  // Path-traversal containment check
+  try {
+    validateAgentName(name, config.workspaces_root);
+  } catch (error) {
+    const msg = error instanceof Error ? error.message : "Ungültiger Agent-Name";
+    await interaction.reply({ content: msg, ephemeral: true });
+    return;
+  }
+
   // Check uniqueness
   if (db.getWorkspaceByName(name)) {
     await interaction.reply({

tests/unit/path-traversal.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect } from "vitest";
+import { validateAgentName } from "../../src/commands/new-agent";
+
+const ROOT = "/tmp/ws";
+
+describe("validateAgentName – path traversal containment", () => {
+  it('throws for "../etc"', () => {
+    expect(() => validateAgentName("../etc", ROOT)).toThrow();
+  });
+
+  it('throws for ".."', () => {
+    expect(() => validateAgentName("..", ROOT)).toThrow();
+  });
+
+  it('does not throw for "a/../b" (resolves to /tmp/ws/b, stays inside root)', () => {
+    // path.resolve("/tmp/ws", "a/../b") => "/tmp/ws/b" -- still inside root
+    expect(() => validateAgentName("a/../b", ROOT)).not.toThrow();
+  });
+
+  it('throws for empty string ""', () => {
+    expect(() => validateAgentName("", ROOT)).toThrow();
+  });
+
+  it('allows "my-agent"', () => {
+    expect(() => validateAgentName("my-agent", ROOT)).not.toThrow();
+  });
+
+  it('allows "agent-123"', () => {
+    expect(() => validateAgentName("agent-123", ROOT)).not.toThrow();
+  });
+});