migrate: run the sweep server-side, and send the whole balance

Two fixes from the first live test:

The POST went out from the browser, where $lib/utils' base is "" — so
it hit the SvelteKit page route and came back "POST method not allowed".
Payments in this app all run server-side with auth(cookies), because
that's where the session token is usable; /migrate is a form action now
like the rest of the send flows.

And the routing reserve is gone: the ASP's node has two direct channels
to ln.coinos.io, so a sweep is one hop and costs nothing. It sends the
full balance, only retrying 0.5% lighter if a payment actually comes
back short.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Wvj4aoeMZwA7VUGdJP9Swi

1 files changed, 67 insertions, 0 deletions

diff --git a/src/routes/(app)/migrate/+page.server.ts b/src/routes/(app)/migrate/+page.server.ts
index 4529c14c..dc3beb02 100644
--- a/src/routes/(app)/migrate/+page.server.ts
+++ b/src/routes/(app)/migrate/+page.server.ts
@@ -1,5 +1,25 @@
+import { auth, post } from "$lib/utils";
 import { redirect } from "@sveltejs/kit";
 
+const REGISTRAR = "https://names.coinos.io";
+
+// An invoice from the v3 registrar for this address and amount (LNURL-pay).
+async function invoiceFor(address: string, sats: number) {
+	const [name, domain] = String(address).split("@");
+	if (!name || !domain) throw new Error("bad destination address");
+	const p = await fetch(
+		`${REGISTRAR}/.well-known/lnurlp/${name}?domain=${encodeURIComponent(domain)}`,
+	).then((r) => r.json());
+	if (!p?.callback) throw new Error(p?.reason || "that address isn't registered on coinos v3 yet");
+	const msat = sats * 1000;
+	if (msat < p.minSendable) throw new Error("balance is below the destination's minimum");
+	if (msat > p.maxSendable) throw new Error("balance is above the destination's maximum");
+	const sep = p.callback.includes("?") ? "&" : "?";
+	const inv = await fetch(`${p.callback}${sep}amount=${msat}`).then((r) => r.json());
+	if (!inv?.pr) throw new Error(inv?.reason || "could not get an invoice");
+	return inv.pr as string;
+}
+
 export async function load({ parent, url }) {
 	const { user } = await parent();
 	if (!user) redirect(307, `/login?redirect=${encodeURIComponent(url.pathname + url.search)}`);
@@ -8,3 +28,50 @@ export async function load({ parent, url }) {
 		back: url.searchParams.get("back") || "",
 	};
 }
+
+export const actions = {
+	default: async ({ cookies, request, url }) => {
+		const form = await request.formData();
+		const to = String(form.get("to") || url.searchParams.get("to") || "");
+		const pin = String(form.get("pin") || "");
+		const balance = Number(form.get("balance") || 0);
+		const username = String(form.get("username") || "");
+		if (!to) return { error: "no destination" };
+
+		let sent = 0;
+		try {
+			if (balance > 0) {
+				// coinos and the ASP peer directly, so a sweep normally costs
+				// nothing. Try the whole balance first and only hold a little
+				// back if the payment actually comes up short.
+				const attempts = [balance, balance - Math.max(1, Math.ceil(balance * 0.005))];
+				let lastErr;
+				for (const amount of attempts) {
+					if (amount <= 0) continue;
+					try {
+						const payreq = await invoiceFor(to, amount);
+						await post("/payments", { payreq, ...(pin ? { pin } : {}) }, auth(cookies));
+						sent = amount;
+						break;
+					} catch (e) {
+						lastErr = e;
+						const msg = String((e as any)?.message || e);
+						// only a shortfall is worth retrying smaller
+						if (!/insufficient|balance|not enough|fee/i.test(msg)) throw e;
+					}
+				}
+				if (!sent) throw lastErr;
+			}
+			// Releasing the username is what lets them keep it on v3.
+			await post(
+				"/user",
+				{ username: `${username}_v2`, ...(pin ? { pin } : {}) },
+				auth(cookies),
+			);
+			return { ok: true, sent, released: username };
+		} catch (e) {
+			const msg = e && typeof e === "object" && "message" in e ? String(e.message) : String(e);
+			return { error: msg, sent };
+		}
+	},
+};