Add active-turn steering (#3394)

* feat(agents): add active-turn steering

Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.

* fix(agents): stabilize steering history and replay QA

* fix(agents): preserve steering timeline order

* fix(agents): reconcile resumed provider history

* fix(agents): serialize steering with cancellation

* test(agents): prove Claude multi-tool steering

* test(agents): force explicit history hydration

* fix(agents): flush output before steer admission

packages/app/e2e/support/helpers/composer.ts

@@ -198,13 +198,20 @@ export async function selectGithubOption(
 export interface MockAgentSetup {
   client: SeedDaemonClient;
   repo: Awaited<ReturnType<typeof createTempGitRepo>>;
+  workspaceId: string;
+  agentId: string;
   cleanup: () => Promise<void>;
 }
 
 /** Create a temp repo, start a mock agent, navigate to it, and wait for it to be running. */
 export async function startRunningMockAgent(
   page: Page,
-  opts: { prefix: string; model: string; prompt: string },
+  opts: {
+    prefix: string;
+    model: string;
+    prompt: string;
+    featureValues?: Record<string, unknown>;
+  },
 ): Promise<MockAgentSetup> {
   const serverId = getServerId();
 
@@ -222,6 +229,7 @@ export async function startRunningMockAgent(
     cwd: repo.path,
     workspaceId: workspace.id,
     model: opts.model,
+    featureValues: opts.featureValues,
   });
   const agentUrl = `${buildHostWorkspaceRoute(serverId, workspace.id)}?open=${encodeURIComponent(`agent:${agent.id}`)}`;
   await page.goto(agentUrl);
@@ -233,6 +241,8 @@ export async function startRunningMockAgent(
   return {
     client,
     repo,
+    workspaceId: workspace.id,
+    agentId: agent.id,
     cleanup: async () => {
       await client.removeProject(workspace.projectId).catch(() => undefined);
       await client.close().catch(() => undefined);