Add honest accounting and automatic refund mechanism for completed jobs

Implement honest accounting post-job completion, calculating actual costs, adding margin, and enabling automatic refunds for overpayments via a new endpoint.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 418bf6f8-212b-4bb0-a7a5-8231a061da4e
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: c6386de2-d5f4-47cc-a557-73416f09e118
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/9f85e954-647c-46a5-90a7-396e495a805a/418bf6f8-212b-4bb0-a7a5-8231a061da4e/sPDHkg8
Replit-Helium-Checkpoint-Created: true

artifacts/api-server/src/lib/lnbits.ts

@@ -26,6 +26,8 @@ export class LNbitsService {
     }
   }
 
+  // ── Inbound invoices ─────────────────────────────────────────────────────
+
   async createInvoice(amountSats: number, memo: string): Promise<LNbitsInvoice> {
     if (this.stubMode) {
       const paymentHash = randomBytes(32).toString("hex");
@@ -34,7 +36,7 @@ export class LNbitsService {
       return { paymentHash, paymentRequest };
     }
 
-    const response = await fetch(`${this.url.replace(/\/$/, "")}/api/v1/payments`, {
+    const response = await fetch(`${this.base()}/api/v1/payments`, {
       method: "POST",
       headers: this.headers(),
       body: JSON.stringify({ out: false, amount: amountSats, memo }),
@@ -58,7 +60,7 @@ export class LNbitsService {
     }
 
     const response = await fetch(
-      `${this.url.replace(/\/$/, "")}/api/v1/payments/${paymentHash}`,
+      `${this.base()}/api/v1/payments/${paymentHash}`,
       { method: "GET", headers: this.headers() },
     );
 
@@ -71,7 +73,68 @@ export class LNbitsService {
     return data.paid;
   }
 
-  /** Stub-only helper: mark an invoice as paid for testing/dev flows. */
+  // ── Outbound payments (refunds) ──────────────────────────────────────────
+
+  /**
+   * Decode a BOLT11 invoice and return its amount in satoshis.
+   * Stub mode: parses the embedded amount from our known stub format (lnbcrtXu1stub_...),
+   * or returns null for externally-generated invoices.
+   */
+  async decodeInvoice(bolt11: string): Promise<{ amountSats: number } | null> {
+    if (this.stubMode) {
+      // Our stub format: lnbcrtNNNu1stub_...  where NNN is the amount in sats
+      const m = bolt11.match(/^lnbcrt(\d+)u1stub_/i);
+      if (m) return { amountSats: parseInt(m[1], 10) };
+      // Unknown format in stub mode — accept blindly (simulated environment)
+      return null;
+    }
+
+    const response = await fetch(`${this.base()}/api/v1/payments/decode`, {
+      method: "POST",
+      headers: this.headers(),
+      body: JSON.stringify({ data: bolt11 }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      throw new Error(`LNbits decodeInvoice failed (${response.status}): ${body}`);
+    }
+
+    const data = (await response.json()) as { amount_msat?: number };
+    if (!data.amount_msat) return null;
+    return { amountSats: Math.floor(data.amount_msat / 1000) };
+  }
+
+  /**
+   * Pay an outgoing BOLT11 invoice (e.g. to return a refund to a user).
+   * Returns the payment hash.
+   * Stub mode: simulates a successful payment.
+   */
+  async payInvoice(bolt11: string): Promise<string> {
+    if (this.stubMode) {
+      const paymentHash = randomBytes(32).toString("hex");
+      console.log(`[stub] Paid outgoing invoice — fake hash=${paymentHash}`);
+      return paymentHash;
+    }
+
+    const response = await fetch(`${this.base()}/api/v1/payments`, {
+      method: "POST",
+      headers: this.headers(),
+      body: JSON.stringify({ out: true, bolt11 }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      throw new Error(`LNbits payInvoice failed (${response.status}): ${body}`);
+    }
+
+    const data = (await response.json()) as { payment_hash: string };
+    return data.payment_hash;
+  }
+
+  // ── Stub helpers ─────────────────────────────────────────────────────────
+
+  /** Stub-only: mark an inbound invoice as paid for testing/dev flows. */
   stubMarkPaid(paymentHash: string): void {
     if (!this.stubMode) {
       throw new Error("stubMarkPaid called on a real LNbitsService instance");
@@ -80,6 +143,12 @@ export class LNbitsService {
     console.log(`[stub] Marked invoice paid: hash=${paymentHash}`);
   }
 
+  // ── Private helpers ──────────────────────────────────────────────────────
+
+  private base(): string {
+    return this.url.replace(/\/$/, "");
+  }
+
   private headers(): Record<string, string> {
     return {
       "Content-Type": "application/json",