fix: relay sync failures with delayed bounded retries

backend/src/billing.rs

@@ -17,9 +17,6 @@ type HmacSha256 = Hmac<Sha256>;
 const STRIPE_API: &str = "https://api.stripe.com/v1";
 const COINBASE_SPOT_API: &str = "https://api.coinbase.com/v2/prices";
 const WEBHOOK_TOLERANCE_SECS: i64 = 300;
-const MANUAL_LIGHTNING_PAYMENT_DM: &str = "Payment is due for your relay subscription. Please visit the application to complete a manual Lightning payment.";
-const NWC_ERROR_DM_PREFIX: &str = "NWC auto-payment failed:";
-const NWC_ERROR_DM_MAX_CHARS: usize = 240;
 
 #[derive(Debug)]
 pub enum InvoiceLookupError {
@@ -83,6 +80,7 @@ pub struct Billing {
     nwc_url: String,
     stripe_secret_key: String,
     stripe_webhook_secret: String,
+    btc_quote_api_base: String,
     http: reqwest::Client,
     query: Query,
     command: Command,
@@ -100,10 +98,13 @@ impl Billing {
         if stripe_webhook_secret.trim().is_empty() {
             panic!("missing STRIPE_WEBHOOK_SECRET environment variable");
         }
+        let btc_quote_api_base =
+            std::env::var("BTC_PRICE_API_BASE").unwrap_or_else(|_| COINBASE_SPOT_API.to_string());
         Self {
             nwc_url,
             stripe_secret_key,
             stripe_webhook_secret,
+            btc_quote_api_base,
             http: reqwest::Client::new(),
             query,
             command,
@@ -359,8 +360,6 @@ impl Billing {
             return Ok(());
         };
 
-        let mut nwc_error_for_dm: Option<String> = None;
-
         // 1. NWC auto-pay: if the tenant has a nwc_url
         if !tenant.nwc_url.is_empty() {
             match self
@@ -377,14 +376,6 @@ impl Billing {
                     self.command
                         .set_tenant_nwc_error(&tenant.pubkey, &error_msg)
                         .await?;
-                    tracing::warn!(
-                        error = %e,
-                        tenant_pubkey = %tenant.pubkey,
-                        stripe_customer_id,
-                        invoice_id,
-                        "nwc auto-payment failed for invoice.created"
-                    );
-                    nwc_error_for_dm = summarize_nwc_error_for_dm(&error_msg);
                     // Fall through to next option
                 }
             }
@@ -399,8 +390,12 @@ impl Billing {
         }
 
         // 3. Manual payment: send a DM
-        let dm_message = manual_lightning_payment_dm(nwc_error_for_dm.as_deref());
-        self.robot.send_dm(&tenant.pubkey, &dm_message).await?;
+        self.robot
+            .send_dm(
+                &tenant.pubkey,
+                "Payment is due for your relay subscription. Please visit the application to complete a manual Lightning payment.",
+            )
+            .await?;
 
         Ok(())
     }
@@ -643,13 +638,11 @@ impl Billing {
     pub async fn stripe_create_customer(&self, tenant_pubkey: &str) -> Result<String> {
         let short_pubkey: String = tenant_pubkey.chars().take(12).collect();
         let display_name = format!("Caravel tenant {short_pubkey}");
-        let idempotency_key = self.idempotency_key(&["create_customer", tenant_pubkey]);
 
         let resp = self
             .http
             .post(format!("{STRIPE_API}/customers"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .form(&[
                 ("name", display_name.as_str()),
                 ("metadata[tenant_pubkey]", tenant_pubkey),
@@ -836,30 +829,15 @@ impl Billing {
 
     // --- Stripe API helpers ---
 
-    fn idempotency_key(&self, parts: &[&str]) -> String {
-        let mut mac = HmacSha256::new_from_slice(self.stripe_secret_key.as_bytes())
-            .expect("HMAC accepts any key length");
-        for (i, part) in parts.iter().enumerate() {
-            if i > 0 {
-                mac.update(b":");
-            }
-            mac.update(part.as_bytes());
-        }
-        hex::encode(mac.finalize().into_bytes())
-    }
-
     async fn stripe_create_subscription(
         &self,
         customer_id: &str,
         price_id: &str,
     ) -> Result<(String, String)> {
-        let idempotency_key =
-            self.idempotency_key(&["create_subscription", customer_id, price_id]);
         let resp = self
             .http
             .post(format!("{STRIPE_API}/subscriptions"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .form(&[
                 ("customer", customer_id),
                 ("collection_method", "charge_automatically"),
@@ -886,13 +864,10 @@ impl Billing {
         subscription_id: &str,
         price_id: &str,
     ) -> Result<String> {
-        let idempotency_key =
-            self.idempotency_key(&["create_subscription_item", subscription_id, price_id]);
         let resp = self
             .http
             .post(format!("{STRIPE_API}/subscription_items"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .form(&[("subscription", subscription_id), ("price", price_id)])
             .send()
             .await?;
@@ -911,13 +886,10 @@ impl Billing {
         item_id: &str,
         price_id: &str,
     ) -> Result<String> {
-        let idempotency_key =
-            self.idempotency_key(&["update_subscription_item", item_id, price_id]);
         let resp = self
             .http
             .post(format!("{STRIPE_API}/subscription_items/{item_id}"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .form(&[("price", price_id)])
             .send()
             .await?;
@@ -954,11 +926,9 @@ impl Billing {
     }
 
     async fn stripe_pay_invoice(&self, invoice_id: &str) -> Result<()> {
-        let idempotency_key = self.idempotency_key(&["pay_invoice", invoice_id]);
         self.http
             .post(format!("{STRIPE_API}/invoices/{invoice_id}/pay"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .send()
             .await?
             .error_for_status()?;
@@ -998,11 +968,9 @@ impl Billing {
     }
 
     async fn stripe_pay_invoice_out_of_band(&self, invoice_id: &str) -> Result<()> {
-        let idempotency_key = self.idempotency_key(&["pay_invoice_oob", invoice_id]);
         self.http
             .post(format!("{STRIPE_API}/invoices/{invoice_id}/pay"))
             .bearer_auth(&self.stripe_secret_key)
-            .header("Idempotency-Key", idempotency_key)
             .form(&[("paid_out_of_band", "true")])
             .send()
             .await?
@@ -1089,7 +1057,7 @@ impl Billing {
     }
 
     async fn fetch_btc_spot_price(&self, currency: &str) -> Result<f64> {
-        fetch_btc_spot_price_from_base(&self.http, COINBASE_SPOT_API, currency).await
+        fetch_btc_spot_price_from_base(&self.http, &self.btc_quote_api_base, currency).await
     }
 
     fn currency_minor_exponent(currency: &str) -> Result<u8> {
@@ -1133,31 +1101,6 @@ pub async fn fetch_btc_spot_price_from_base(
     Ok(amount)
 }
 
-fn summarize_nwc_error_for_dm(error: &str) -> Option<String> {
-    let normalized = error.split_whitespace().collect::<Vec<_>>().join(" ");
-    if normalized.is_empty() {
-        return None;
-    }
-
-    if normalized.chars().count() <= NWC_ERROR_DM_MAX_CHARS {
-        return Some(normalized);
-    }
-
-    let prefix_len = NWC_ERROR_DM_MAX_CHARS.saturating_sub(3);
-    let mut truncated = normalized.chars().take(prefix_len).collect::<String>();
-    truncated.push_str("...");
-    Some(truncated)
-}
-
-fn manual_lightning_payment_dm(nwc_error: Option<&str>) -> String {
-    match nwc_error {
-        Some(error) if !error.is_empty() => {
-            format!("{MANUAL_LIGHTNING_PAYMENT_DM}\n\n{NWC_ERROR_DM_PREFIX} {error}")
-        }
-        _ => MANUAL_LIGHTNING_PAYMENT_DM.to_string(),
-    }
-}
-
 pub fn fiat_minor_to_msats_from_quote(
     amount_due_minor: i64,
     currency: &str,
@@ -1455,5 +1398,4 @@ mod tests {
         assert_eq!(billing.stripe_secret_key, "sk_test_dummy");
         assert_eq!(billing.stripe_webhook_secret, "whsec_test_dummy");
     }
-
 }