Add optional export filename, tests for post-implement features

Add optional filename field to export dialog with automatic .json
extension handling. Extract resolveFilename() for testability. Add
tests for includeHistory flag, bundleToJson, and filename resolution.
Add export format compatibility note to CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/components/export-method-dialog.tsx

@@ -2,10 +2,11 @@ import { Check, ClipboardCopy, Download, X } from "lucide-react";
 import { useCallback, useState } from "react";
 import { Button } from "./ui/button.js";
 import { Dialog } from "./ui/dialog.js";
+import { Input } from "./ui/input.js";
 
 interface ExportMethodDialogProps {
 	open: boolean;
-	onDownload: (includeHistory: boolean) => void;
+	onDownload: (includeHistory: boolean, filename: string) => void;
 	onCopyToClipboard: (includeHistory: boolean) => void;
 	onClose: () => void;
 }
@@ -17,10 +18,12 @@ export function ExportMethodDialog({
 	onClose,
 }: Readonly<ExportMethodDialogProps>) {
 	const [includeHistory, setIncludeHistory] = useState(false);
+	const [filename, setFilename] = useState("");
 	const [copied, setCopied] = useState(false);
 
 	const handleClose = useCallback(() => {
 		setIncludeHistory(false);
+		setFilename("");
 		setCopied(false);
 		onClose();
 	}, [onClose]);
@@ -39,6 +42,14 @@ export function ExportMethodDialog({
 					<X className="h-4 w-4" />
 				</Button>
 			</div>
+			<div className="mb-3">
+				<Input
+					type="text"
+					value={filename}
+					onChange={(e) => setFilename(e.target.value)}
+					placeholder="Filename (optional)"
+				/>
+			</div>
 			<label className="mb-4 flex items-center gap-2 text-sm">
 				<input
 					type="checkbox"
@@ -53,7 +64,7 @@ export function ExportMethodDialog({
 					type="button"
 					className="flex items-center gap-3 rounded-lg border border-border px-4 py-3 text-left text-foreground text-sm hover:bg-hover-neutral-bg"
 					onClick={() => {
-						onDownload(includeHistory);
+						onDownload(includeHistory, filename);
 						handleClose();
 					}}
 				>