feat(25-02): create ChatFileDropZone and integrate into ChatInput

- Create ChatFileDropZone component with drag-and-drop state and overlay
- Add onFilesPicked/pendingFiles/onRemoveFile props to ChatInput
- Wrap form in ChatFileDropZone for drag-and-drop support
- Add handlePaste for clipboard image paste (clipboardData.files)
- Add Paperclip icon button with hidden file input for file picker
- Show pending file chips above textarea with progress and remove button
- Add tests: renders file attach button, calls onFilesPicked, shows pending chips

ui/src/components/ChatFileDropZone.tsx

@@ -0,0 +1,67 @@
+import { useState } from "react";
+import { cn } from "../lib/utils";
+
+interface ChatFileDropZoneProps {
+  onFilesDropped: (files: File[]) => void;
+  disabled?: boolean;
+  children: React.ReactNode;
+}
+
+export function ChatFileDropZone({ onFilesDropped, disabled = false, children }: ChatFileDropZoneProps) {
+  const [isDragOver, setIsDragOver] = useState(false);
+
+  function handleDragEnter(e: React.DragEvent) {
+    e.preventDefault();
+    e.stopPropagation();
+    if (!disabled) setIsDragOver(true);
+  }
+
+  function handleDragLeave(e: React.DragEvent) {
+    e.preventDefault();
+    e.stopPropagation();
+    // Only set false if leaving the outer element (not entering a child)
+    if (e.currentTarget === e.target || !e.currentTarget.contains(e.relatedTarget as Node)) {
+      setIsDragOver(false);
+    }
+  }
+
+  function handleDragOver(e: React.DragEvent) {
+    e.preventDefault();
+    e.stopPropagation();
+    if (!disabled) setIsDragOver(true);
+  }
+
+  function handleDrop(e: React.DragEvent) {
+    e.preventDefault();
+    e.stopPropagation();
+    setIsDragOver(false);
+    if (disabled) return;
+    const files = Array.from(e.dataTransfer.files);
+    if (files.length > 0) {
+      onFilesDropped(files);
+    }
+  }
+
+  return (
+    <div
+      className="relative"
+      onDragEnter={handleDragEnter}
+      onDragLeave={handleDragLeave}
+      onDragOver={handleDragOver}
+      onDrop={handleDrop}
+    >
+      {children}
+      {isDragOver && (
+        <div
+          className={cn(
+            "absolute inset-0 z-10 flex items-center justify-center rounded-md",
+            "bg-primary/10 border-2 border-dashed border-primary",
+            "pointer-events-none",
+          )}
+        >
+          <span className="text-sm font-medium text-primary">Drop files here</span>
+        </div>
+      )}
+    </div>
+  );
+}

ui/src/components/ChatInput.test.tsx

@@ -163,4 +163,57 @@ describe("ChatInput", () => {
       expect(btn!.disabled).toBe(true);
     });
   });
+
+  describe("file upload (FILE-05)", () => {
+    it("renders file attach button", () => {
+      const onSend = vi.fn();
+      renderChatInput({ onSend });
+      const fileInput = container.querySelector("input[type='file']");
+      expect(fileInput).not.toBeNull();
+    });
+
+    it("calls onFilesPicked when file input changes", () => {
+      const onSend = vi.fn();
+      const onFilesPicked = vi.fn();
+      root = createRoot(container);
+      act(() => {
+        root!.render(<ChatInput onSend={onSend} onFilesPicked={onFilesPicked} />);
+      });
+      const fileInput = container.querySelector("input[type='file']") as HTMLInputElement;
+      expect(fileInput).not.toBeNull();
+
+      const mockFile = new File(["content"], "test.txt", { type: "text/plain" });
+      act(() => {
+        Object.defineProperty(fileInput, "files", {
+          value: [mockFile],
+          writable: false,
+        });
+        fileInput.dispatchEvent(new Event("change", { bubbles: true }));
+      });
+
+      expect(onFilesPicked).toHaveBeenCalledWith([mockFile]);
+    });
+
+    it("shows pending file chips", () => {
+      const onSend = vi.fn();
+      const pendingFiles = [
+        {
+          id: "temp-1",
+          file: new File([], "image.png"),
+          name: "image.png",
+          mimeType: "image/png",
+          sizeBytes: 1024,
+          progress: 50,
+          status: "uploading" as const,
+        },
+      ];
+      root = createRoot(container);
+      act(() => {
+        root!.render(<ChatInput onSend={onSend} pendingFiles={pendingFiles} />);
+      });
+      const chip = container.querySelector(".bg-muted");
+      expect(chip).not.toBeNull();
+      expect(chip!.textContent).toContain("image.png");
+    });
+  });
 });

ui/src/components/ChatInput.tsx

@@ -1,10 +1,12 @@
 import { useEffect, useRef, useState } from "react";
-import { Send, Loader2 } from "lucide-react";
+import { Send, Loader2, Paperclip, X } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { ChatSlashCommandPopover } from "./ChatSlashCommandPopover";
 import { ChatMentionPopover } from "./ChatMentionPopover";
+import { ChatFileDropZone } from "./ChatFileDropZone";
 import { cn } from "../lib/utils";
 import type { Agent } from "@paperclipai/shared";
+import type { PendingFile } from "../hooks/useChatFileUpload";
 
 interface ChatInputProps {
   onSend: (content: string) => void;
@@ -14,6 +16,10 @@ interface ChatInputProps {
   // Popover support
   agents?: Agent[];
   agentsLoading?: boolean;
+  // File upload support
+  onFilesPicked?: (files: File[]) => void;
+  pendingFiles?: PendingFile[];
+  onRemoveFile?: (id: string) => void;
 }
 
 export function ChatInput({
@@ -23,6 +29,9 @@ export function ChatInput({
   placeholder = "Message your agent...",
   agents = [],
   agentsLoading = false,
+  onFilesPicked,
+  pendingFiles,
+  onRemoveFile,
 }: ChatInputProps) {
   const [value, setValue] = useState("");
   const textareaRef = useRef<HTMLTextAreaElement>(null);
@@ -115,6 +124,15 @@ export function ChatInput({
     // Shift+Enter falls through to default behavior (inserts newline)
   }
 
+  function handlePaste(e: React.ClipboardEvent) {
+    const files = Array.from(e.clipboardData.files);
+    if (files.length > 0) {
+      e.preventDefault();
+      onFilesPicked?.(files);
+    }
+    // If no files, allow default paste behavior (text)
+  }
+
   const isEmpty = value.trim().length === 0;
 
   const textarea = (
@@ -123,6 +141,7 @@ export function ChatInput({
       value={value}
       onChange={handleChange}
       onKeyDown={handleKeyDown}
+      onPaste={handlePaste}
       placeholder={placeholder}
       rows={1}
       disabled={disabled}
@@ -139,48 +158,95 @@ export function ChatInput({
   );
 
   return (
-    <form
+    <ChatFileDropZone
-      onSubmit={(e) => {
+      onFilesDropped={(files) => files.forEach((f) => onFilesPicked?.([f]))}
-        e.preventDefault();
+      disabled={disabled}
-        submit();
-      }}
-      className="flex items-end gap-2"
     >
-      {/* Slash command takes priority over mention popover */}
+      <form
-      <div className="flex-1 relative">
+        onSubmit={(e) => {
-        <ChatSlashCommandPopover
+          e.preventDefault();
-          open={slashOpen && !mentionOpen}
+          submit();
-          onOpenChange={setSlashOpen}
+        }}
-          onSelect={handleSlashSelect}
+        className="flex items-end gap-2"
-          query={slashQuery}
-        >
-          <ChatMentionPopover
-            open={mentionOpen && !slashOpen}
-            onOpenChange={setMentionOpen}
-            onSelect={handleMentionSelect}
-            query={mentionQuery}
-            agents={agents}
-            isLoading={agentsLoading}
-          >
-            {textarea}
-          </ChatMentionPopover>
-        </ChatSlashCommandPopover>
-      </div>
-
-      <Button
-        type="submit"
-        variant="ghost"
-        size="icon"
-        disabled={isEmpty || isSubmitting || disabled}
-        aria-label="Send message"
-        className="shrink-0"
       >
-        {isSubmitting ? (
+        {/* Slash command takes priority over mention popover */}
-          <Loader2 className="h-4 w-4 animate-spin" />
+        <div className="flex-1 relative">
-        ) : (
+          {/* Pending file chips above textarea */}
-          <Send className="h-4 w-4" />
+          {pendingFiles && pendingFiles.length > 0 && (
-        )}
+            <div className="flex flex-wrap gap-1 px-1 pb-1">
-      </Button>
+              {pendingFiles.map((pf) => (
-    </form>
+                <div key={pf.id} className="flex items-center gap-1 rounded bg-muted px-2 py-1 text-xs">
+                  {pf.status === "uploading" && (
+                    <Loader2 className="h-3 w-3 animate-spin" />
+                  )}
+                  <span className="max-w-[120px] truncate">{pf.name}</span>
+                  {pf.status === "uploading" && (
+                    <span className="text-muted-foreground">{pf.progress}%</span>
+                  )}
+                  <button
+                    type="button"
+                    className="ml-1 text-muted-foreground hover:text-foreground"
+                    onClick={() => onRemoveFile?.(pf.id)}
+                  >
+                    <X className="h-3 w-3" />
+                  </button>
+                </div>
+              ))}
+            </div>
+          )}
+
+          <ChatSlashCommandPopover
+            open={slashOpen && !mentionOpen}
+            onOpenChange={setSlashOpen}
+            onSelect={handleSlashSelect}
+            query={slashQuery}
+          >
+            <ChatMentionPopover
+              open={mentionOpen && !slashOpen}
+              onOpenChange={setMentionOpen}
+              onSelect={handleMentionSelect}
+              query={mentionQuery}
+              agents={agents}
+              isLoading={agentsLoading}
+            >
+              {textarea}
+            </ChatMentionPopover>
+          </ChatSlashCommandPopover>
+        </div>
+
+        {/* File attach button */}
+        <label className="shrink-0 cursor-pointer">
+          <input
+            type="file"
+            multiple
+            className="hidden"
+            onChange={(e) => {
+              const files = Array.from(e.target.files ?? []);
+              if (files.length > 0) onFilesPicked?.(files);
+              e.target.value = ""; // reset for re-selection
+            }}
+            disabled={disabled}
+          />
+          <Button type="button" variant="ghost" size="icon" asChild disabled={disabled}>
+            <span><Paperclip className="h-4 w-4" /></span>
+          </Button>
+        </label>
+
+        <Button
+          type="submit"
+          variant="ghost"
+          size="icon"
+          disabled={isEmpty || isSubmitting || disabled}
+          aria-label="Send message"
+          className="shrink-0"
+        >
+          {isSubmitting ? (
+            <Loader2 className="h-4 w-4 animate-spin" />
+          ) : (
+            <Send className="h-4 w-4" />
+          )}
+        </Button>
+      </form>
+    </ChatFileDropZone>
   );
 }