feat(21-02): add ChatInput component with auto-resize and keyboard shortcuts

- Auto-resize textarea from 1 to 6 lines (max-height 160px)
- Enter sends message and clears input
- Shift+Enter inserts newline without sending
- Escape clears input when non-empty, calls onClose when empty
- Disabled state and loading spinner when isSubmitting=true
- Accessible: aria-label on textarea and send button
- 9 tests green (jsdom environment)

ui/src/components/ChatInput.test.tsx

@@ -0,0 +1,162 @@
+// @vitest-environment jsdom
+
+import { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { ChatInput } from "./ChatInput";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+(globalThis as any).IS_REACT_ACT_ENVIRONMENT = true;
+
+describe("ChatInput", () => {
+  let container: HTMLDivElement;
+  let root: ReturnType<typeof createRoot>;
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+  });
+
+  afterEach(() => {
+    act(() => {
+      root.unmount();
+    });
+    container.remove();
+  });
+
+  function getTextarea(): HTMLTextAreaElement {
+    return container.querySelector('[aria-label="Message input"]') as HTMLTextAreaElement;
+  }
+
+  function getSendButton(): HTMLButtonElement {
+    return container.querySelector('[aria-label="Send message"]') as HTMLButtonElement;
+  }
+
+  it("renders textarea with aria-label='Message input'", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} />);
+    });
+    expect(getTextarea()).not.toBeNull();
+  });
+
+  it("renders send button with aria-label='Send message'", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} />);
+    });
+    expect(getSendButton()).not.toBeNull();
+  });
+
+  it("send button is disabled when input is empty", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} />);
+    });
+    expect(getSendButton().disabled).toBe(true);
+  });
+
+  it("Enter key calls onSend with current value and clears input", () => {
+    const onSend = vi.fn();
+    act(() => {
+      root.render(<ChatInput onSend={onSend} />);
+    });
+
+    const textarea = getTextarea();
+
+    // Type some text
+    act(() => {
+      const event = new Event("input", { bubbles: true });
+      Object.defineProperty(textarea, "value", { value: "hello", writable: true, configurable: true });
+      textarea.dispatchEvent(new Event("input", { bubbles: true }));
+    });
+
+    // Simulate React-controlled input change
+    act(() => {
+      const nativeInputValueSetter = Object.getOwnPropertyDescriptor(HTMLTextAreaElement.prototype, "value")?.set;
+      nativeInputValueSetter?.call(textarea, "hello");
+      textarea.dispatchEvent(new Event("input", { bubbles: true }));
+    });
+
+    // Fire Enter keydown
+    act(() => {
+      textarea.dispatchEvent(
+        new KeyboardEvent("keydown", { key: "Enter", shiftKey: false, bubbles: true }),
+      );
+    });
+
+    expect(onSend).toHaveBeenCalledWith("hello");
+    expect(getTextarea().value).toBe("");
+  });
+
+  it("Shift+Enter does not call onSend", () => {
+    const onSend = vi.fn();
+    act(() => {
+      root.render(<ChatInput onSend={onSend} />);
+    });
+
+    const textarea = getTextarea();
+    act(() => {
+      const nativeInputValueSetter = Object.getOwnPropertyDescriptor(HTMLTextAreaElement.prototype, "value")?.set;
+      nativeInputValueSetter?.call(textarea, "hello");
+      textarea.dispatchEvent(new Event("input", { bubbles: true }));
+    });
+
+    act(() => {
+      textarea.dispatchEvent(
+        new KeyboardEvent("keydown", { key: "Enter", shiftKey: true, bubbles: true }),
+      );
+    });
+
+    expect(onSend).not.toHaveBeenCalled();
+  });
+
+  it("Escape clears input when input has content", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} />);
+    });
+
+    const textarea = getTextarea();
+    act(() => {
+      const nativeInputValueSetter = Object.getOwnPropertyDescriptor(HTMLTextAreaElement.prototype, "value")?.set;
+      nativeInputValueSetter?.call(textarea, "some text");
+      textarea.dispatchEvent(new Event("input", { bubbles: true }));
+    });
+
+    act(() => {
+      textarea.dispatchEvent(
+        new KeyboardEvent("keydown", { key: "Escape", bubbles: true }),
+      );
+    });
+
+    expect(getTextarea().value).toBe("");
+  });
+
+  it("Escape calls onClose when input is empty", () => {
+    const onClose = vi.fn();
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} onClose={onClose} />);
+    });
+
+    const textarea = getTextarea();
+    act(() => {
+      textarea.dispatchEvent(
+        new KeyboardEvent("keydown", { key: "Escape", bubbles: true }),
+      );
+    });
+
+    expect(onClose).toHaveBeenCalledTimes(1);
+  });
+
+  it("textarea is disabled when isSubmitting=true", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} isSubmitting />);
+    });
+    expect(getTextarea().disabled).toBe(true);
+  });
+
+  it("send button is disabled when isSubmitting=true", () => {
+    act(() => {
+      root.render(<ChatInput onSend={() => {}} isSubmitting />);
+    });
+    expect(getSendButton().disabled).toBe(true);
+  });
+});

ui/src/components/ChatInput.tsx

@@ -0,0 +1,95 @@
+import { useCallback, useRef, useState, type KeyboardEvent } from "react";
+import { Loader2, Send } from "lucide-react";
+import { cn } from "../lib/utils";
+import { Button } from "@/components/ui/button";
+
+interface ChatInputProps {
+  onSend: (content: string) => void;
+  onClose?: () => void;
+  isSubmitting?: boolean;
+  className?: string;
+}
+
+export function ChatInput({ onSend, onClose, isSubmitting = false, className }: ChatInputProps) {
+  const [value, setValue] = useState("");
+  const textareaRef = useRef<HTMLTextAreaElement>(null);
+
+  const adjustHeight = useCallback(() => {
+    const el = textareaRef.current;
+    if (!el) return;
+    el.style.height = "auto";
+    el.style.height = Math.min(el.scrollHeight, 160) + "px";
+  }, []);
+
+  const handleSend = useCallback(() => {
+    const trimmed = value.trim();
+    if (!trimmed || isSubmitting) return;
+    onSend(trimmed);
+    setValue("");
+    if (textareaRef.current) {
+      textareaRef.current.style.height = "auto";
+    }
+  }, [value, isSubmitting, onSend]);
+
+  const handleKeyDown = useCallback(
+    (e: KeyboardEvent<HTMLTextAreaElement>) => {
+      if (e.key === "Enter" && !e.shiftKey) {
+        e.preventDefault();
+        handleSend();
+      } else if (e.key === "Escape") {
+        e.preventDefault();
+        if (value.trim()) {
+          setValue("");
+          if (textareaRef.current) {
+            textareaRef.current.style.height = "auto";
+          }
+        } else {
+          onClose?.();
+        }
+      }
+    },
+    [handleSend, value, onClose],
+  );
+
+  const isEmpty = value.trim().length === 0;
+
+  return (
+    <div className={cn("flex items-end gap-2 border-t border-border p-3", className)}>
+      <textarea
+        ref={textareaRef}
+        value={value}
+        onChange={(e) => {
+          setValue(e.target.value);
+          adjustHeight();
+        }}
+        onKeyDown={handleKeyDown}
+        placeholder="Send a message..."
+        disabled={isSubmitting}
+        aria-label="Message input"
+        className={cn(
+          "flex-1 resize-none bg-muted border border-border px-3 py-2 text-sm",
+          "placeholder:text-muted-foreground",
+          "focus:outline-none focus:ring-1 focus:ring-ring",
+          "disabled:opacity-50 disabled:cursor-not-allowed",
+        )}
+        style={{ minHeight: 40, maxHeight: 160, fieldSizing: "content" } as React.CSSProperties & { fieldSizing?: string }}
+        rows={1}
+      />
+      <Button
+        variant="default"
+        size="icon"
+        onClick={handleSend}
+        disabled={isEmpty || isSubmitting}
+        aria-label="Send message"
+        aria-disabled={isEmpty || isSubmitting}
+        className="h-10 w-10 shrink-0"
+      >
+        {isSubmitting ? (
+          <Loader2 className="h-4 w-4 animate-spin" />
+        ) : (
+          <Send className="h-4 w-4" />
+        )}
+      </Button>
+    </div>
+  );
+}