feat(server): improve calendar sync queue (#14783)

#### PR Dependency Tree


* **PR #14783** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
  * Configurable request timeout for calendar integrations.
* Calendar polling now enqueues per-subscription sync jobs (larger
batch) for improved throughput.

* **Bug Fixes / Improvements**
* Persisted next-sync timestamps and retry counts for more reliable
scheduling and retry behavior.
* Exponential backoff and webhook renewal now update scheduling
consistently.

* **Refactor**
* Calendar sync flow moved to a job-queue-driven design for better
concurrency and observability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/models/calendar-account.ts

@@ -92,7 +92,7 @@ export class CalendarAccountModel extends BaseModel {
       scope: input.scope ?? null,
       status: input.status ?? 'active',
       lastError: input.lastError ?? null,
-      refreshIntervalMinutes: input.refreshIntervalMinutes ?? 60,
+      refreshIntervalMinutes: input.refreshIntervalMinutes ?? 30,
     };
 
     const updateData: Prisma.CalendarAccountUncheckedUpdateInput = {

packages/backend/server/src/models/calendar-subscription.ts

@@ -17,6 +17,8 @@ export interface UpsertCalendarSubscriptionInput {
 export interface UpdateCalendarSubscriptionSyncInput {
   syncToken?: string | null;
   lastSyncAt?: Date | null;
+  nextSyncAt?: Date;
+  syncRetryCount?: number;
 }
 
 export interface UpdateCalendarSubscriptionChannelInput {
@@ -81,13 +83,21 @@ export class CalendarSubscriptionModel extends BaseModel {
   }
 
   async updateSync(id: string, input: UpdateCalendarSubscriptionSyncInput) {
-    return await this.db.calendarSubscription.update({
-      where: { id },
-      data: {
-        syncToken: input.syncToken ?? null,
-        lastSyncAt: input.lastSyncAt ?? null,
-      },
-    });
+    const data: Prisma.CalendarSubscriptionUncheckedUpdateInput = {};
+    if (input.syncToken !== undefined) {
+      data.syncToken = input.syncToken ?? null;
+    }
+    if (input.lastSyncAt !== undefined) {
+      data.lastSyncAt = input.lastSyncAt ?? null;
+    }
+    if (input.nextSyncAt !== undefined) {
+      data.nextSyncAt = input.nextSyncAt;
+    }
+    if (input.syncRetryCount !== undefined) {
+      data.syncRetryCount = input.syncRetryCount;
+    }
+
+    return await this.db.calendarSubscription.update({ where: { id }, data });
   }
 
   async updateChannel(
@@ -155,10 +165,16 @@ export class CalendarSubscriptionModel extends BaseModel {
     });
   }
 
-  async listAllWithAccountForSync() {
+  async listDueForSync(now: Date, limit: number) {
     return await this.db.calendarSubscription.findMany({
-      where: { enabled: true },
-      include: { account: true },
+      where: {
+        enabled: true,
+        nextSyncAt: { lte: now },
+        account: { status: 'active' },
+      },
+      select: { id: true },
+      orderBy: { nextSyncAt: 'asc' },
+      take: limit,
     });
   }
 
@@ -169,13 +185,6 @@ export class CalendarSubscriptionModel extends BaseModel {
     });
   }
 
-  async updateLastSyncAt(id: string, lastSyncAt: Date) {
-    return await this.db.calendarSubscription.update({
-      where: { id },
-      data: { lastSyncAt },
-    });
-  }
-
   async clearSyncTokensByAccount(accountId: string) {
     return await this.db.calendarSubscription.updateMany({
       where: { accountId },
@@ -200,6 +209,7 @@ export class CalendarSubscriptionModel extends BaseModel {
       data: {
         enabled: false,
         syncToken: null,
+        syncRetryCount: 0,
         customChannelId: null,
         customResourceId: null,
         channelExpiration: null,