feat(FN-4153): complete Step 6 — add general ephemeral agents toggle

Fusion-Task-Id: FN-4153
Fusion-Task-Lineage: 6ec09467-c7a0-4a9d-9a09-16d5ef6f7a86

packages/dashboard/app/components/SettingsModal.tsx

@@ -1975,6 +1975,22 @@ export function SettingsModal({
               </label>
               <small>When enabled, AI-generated task specifications require manual approval before moving to Todo</small>
             </div>
+            <div className="form-group">
+              <label htmlFor="ephemeralAgentsEnabled" className="checkbox-label">
+                <input
+                  id="ephemeralAgentsEnabled"
+                  type="checkbox"
+                  checked={form.ephemeralAgentsEnabled !== false}
+                  onChange={(e) =>
+                    setForm((f) => ({ ...f, ephemeralAgentsEnabled: e.target.checked }))
+                  }
+                />
+                Use ephemeral task-worker agents
+              </label>
+              <small>
+                When enabled (default), Fusion spawns short-lived <code>executor-FN-XXXX</code> agents to run each task. When disabled, only permanent agents execute tasks and the scheduler auto-assigns work using the agent reporting chain. Tasks with no eligible permanent agent stay queued.
+              </small>
+            </div>
             <div className="form-group">
               <label htmlFor="completionDocumentationMode">Completion Documentation Automation</label>
               <select