P1 exit: chat UI, sessions column, agent create — 11 E2E journeys green

- Stream layer: incremental SSE parser tested against bytes captured from
  the REAL gateway (chunking-independent, UTF-8-safe, heartbeat-tolerant);
  Zod gateway event schemas; pure transcript reducer (optimistic send,
  delta streaming, step traces, resume dedupe, error states)
- Same-origin /api proxy route: httpOnly cookie -> bearer, unbuffered SSE
  passthrough; NuqsAdapter in root layout
- Chat workspace: route /claws/{id}/chat/{key} (RSC history + settings),
  WelcomeState with suggested prompts, MessageList (right user bubbles,
  left agent messages, blink caret), collapsible StepTrace, Composer
  (Enter sends, Shift+Enter newline)
- SessionsColumn in 208px SlidePanel (?sessions=1): search, relative
  times, active coral border, new session; /claws/{id} resumes latest or
  opens fresh; minimal create-claw form; rail + button and roster links
- P1 exit E2E: scripted reply streams, tool step trace survives reload,
  separate transcripts across sessions with column switching, create claw
  and chat immediately

83 Rust + 56 frontend unit/component tests + 11 Playwright journeys.

Co-Authored-By: Claude Fable 5 <[email protected]>

frontend/src/components/chat/Composer.test.tsx

@@ -0,0 +1,47 @@
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { describe, expect, it, vi } from "vitest";
+
+import { Composer } from "./Composer";
+
+describe("Composer", () => {
+  it("sends trimmed text on Enter and clears", async () => {
+    const user = userEvent.setup();
+    const onSend = vi.fn();
+    render(<Composer agentName="Scout" disabled={false} onSend={onSend} />);
+    const box = screen.getByLabelText("Message Scout");
+
+    await user.type(box, "  hello there  {Enter}");
+    expect(onSend).toHaveBeenCalledWith("hello there");
+    expect(box).toHaveValue("");
+  });
+
+  it("Shift+Enter inserts a newline instead of sending", async () => {
+    const user = userEvent.setup();
+    const onSend = vi.fn();
+    render(<Composer agentName="Scout" disabled={false} onSend={onSend} />);
+    const box = screen.getByLabelText("Message Scout");
+
+    await user.type(box, "line one{Shift>}{Enter}{/Shift}line two");
+    expect(onSend).not.toHaveBeenCalled();
+    expect(box).toHaveValue("line one\nline two");
+  });
+
+  it("does not send empty input", async () => {
+    const user = userEvent.setup();
+    const onSend = vi.fn();
+    render(<Composer agentName="Scout" disabled={false} onSend={onSend} />);
+    await user.type(screen.getByLabelText("Message Scout"), "   {Enter}");
+    expect(onSend).not.toHaveBeenCalled();
+  });
+
+  it("blocks sending while streaming", async () => {
+    const user = userEvent.setup();
+    const onSend = vi.fn();
+    render(<Composer agentName="Scout" disabled onSend={onSend} />);
+    const box = screen.getByLabelText("Message Scout");
+    await user.type(box, "hi{Enter}");
+    expect(onSend).not.toHaveBeenCalled();
+    expect(screen.getByRole("button", { name: "Send" })).toBeDisabled();
+  });
+});