debounce subscription syncing

src/app/mail/index.ts

@@ -1,4 +1,4 @@
-import {hash, maybe, spec, throttle} from "@welshman/lib"
+import {call, hash, maybe, spec, throttle} from "@welshman/lib"
 import type {Filter} from "@welshman/util"
 import {Address, DELETE, MESSAGE, makeEvent, makeHttpAuth, makeHttpAuthHeader} from "@welshman/util"
 import {merged} from "@welshman/store"
@@ -75,12 +75,22 @@ const syncRelaySubscriptionsForEmail = (
 export class MailNotifications {
   _controller = maybe<AbortController>()
 
+  // In-flight register promise, so overlapping calls (settings page submit plus
+  // Mail.sync) coalesce into a single PUT instead of racing two subscriptions.
+  _register = maybe<Promise<void>>()
+
   async register(email: string, frequency: string) {
+    if (this._register) return this._register
+
+    this._register = call(async () => {
+      try {
         const $user = User.require(app.get())
         const $signer = $user.signer
 
         if (!$signer) {
-      emailNotificationState.set({error: "No signer available. Check your browser extension."})
+          emailNotificationState.set({
+            error: "No signer available. Check your browser extension.",
+          })
           throw new Error("No signer available")
         }
 
@@ -93,7 +103,9 @@ export class MailNotifications {
         try {
           authEvent = await $signer.sign(await makeHttpAuth(EMAIL_NOTIFICATION_SERVER, "PUT"))
         } catch (e) {
-      emailNotificationState.set({error: "Failed to create authentication. Check your signer."})
+          emailNotificationState.set({
+            error: "Failed to create authentication. Check your signer.",
+          })
           throw new Error("Failed to sign NIP-98 auth", {cause: e})
         }
 
@@ -107,7 +119,9 @@ export class MailNotifications {
             headers: {Authorization: authHeader, "Content-Type": "application/json"},
           })
         } catch (e) {
-      emailNotificationState.set({error: `Could not reach email server. Check your connection.`})
+          emailNotificationState.set({
+            error: `Could not reach email server. Check your connection.`,
+          })
           throw new Error("Network error", {cause: e})
         }
 
@@ -119,6 +133,12 @@ export class MailNotifications {
 
         const {key, callback} = await res.json()
         emailNotificationState.set({key, callback, email, frequency, error: undefined})
+      } finally {
+        this._register = undefined
+      }
+    })
+
+    return this._register
   }
 
   async unregister() {