feat: add extractImageFromClipboard utility with broad image/* MIME matching

src/lib/clipboard-image.ts

@@ -0,0 +1,45 @@
+/**
+ * Extracts the first image File from a DataTransfer object.
+ *
+ * Resolution order (most → least reliable across browsers/OS):
+ *   1. clipboardData.files  – browser-normalised FileList; Chrome/Linux/Mac/Safari
+ *      all populate this for real paste events. Most reliable.
+ *   2. clipboardData.items  – DataTransferItemList fallback for edge cases where
+ *      files is empty but items contains a "file" kind entry.
+ *
+ * MIME matching: type.startsWith("image/") intentionally accepts any image
+ * subtype, including OS-specific variants like "image/x-png" on Linux that
+ * a strict allowlist (["image/png", ...]) would silently reject.
+ *
+ * The caller (onImageSelect / handleImageSelect) still runs validateImageFile
+ * which enforces the app's supported format allowlist — so we stay permissive
+ * here and strict at the validation boundary.
+ */
+export function extractImageFromClipboard(
+	clipboardData: DataTransfer | null | undefined,
+): File | null {
+	if (!clipboardData) return null;
+
+	// ── 1. files array (primary) ──────────────────────────────────────────────
+	const { files } = clipboardData;
+	if (files?.length) {
+		for (let i = 0; i < files.length; i++) {
+			const file = files[i];
+			if (file.type.startsWith("image/")) return file;
+		}
+	}
+
+	// ── 2. items fallback ─────────────────────────────────────────────────────
+	const { items } = clipboardData;
+	if (items?.length) {
+		for (let i = 0; i < items.length; i++) {
+			const item = items[i];
+			if (item.kind === "file" && item.type.startsWith("image/")) {
+				const file = item.getAsFile();
+				if (file) return file;
+			}
+		}
+	}
+
+	return null;
+}