Ensure no history gets overwritten.

src/lib/history.ts

@@ -8,6 +8,9 @@ export class History {
 	) {}
 
 	public async push(value: Message) {
+		const content = await Deno.readTextFile(this.path)
+		const { messages } = JSON.parse(content)
+		this.messages = messages
 		this.messages.push(value)
 		while (this.messages.length > this.limit) this.messages.splice(0, 1)
 		await this.save()