Back off plugin job scheduler when DB is down

Pause plugin job scheduler ticks after database connection-refused errors to avoid repeated failed polling while the database is unavailable.

server/src/services/plugin-job-scheduler.ts

@@ -38,6 +38,7 @@ import { and, eq, lte, or } from "drizzle-orm";
 import type { Db } from "@penclipai/db";
 import { pluginJobs, pluginJobRuns } from "@penclipai/db";
 import type { PluginJobStore } from "./plugin-job-store.js";
+import { createDatabaseUnavailableGuard } from "../database-unavailable-guard.js";
 import type { PluginWorkerManager } from "./plugin-worker-manager.js";
 import { parseCron, nextCronTick, validateCron } from "./cron.js";
 import { logger } from "../middleware/logger.js";
@@ -213,6 +214,11 @@ export function createPluginJobScheduler(
   } = options;
 
   const log = logger.child({ service: "plugin-job-scheduler" });
+  const databaseGuard = createDatabaseUnavailableGuard({
+    service: "plugin-job-scheduler",
+    cooldownMs: Math.max(tickIntervalMs * 4, 60_000),
+    logger: log,
+  });
 
   // -----------------------------------------------------------------------
   // State
@@ -244,6 +250,10 @@ export function createPluginJobScheduler(
    * A single scheduler tick. Queries for due jobs and dispatches them.
    */
   async function tick(): Promise<void> {
+    if (!databaseGuard.shouldRun()) {
+      return;
+    }
+
     // Prevent overlapping ticks (in case a tick takes longer than the interval)
     if (tickInProgress) {
       log.debug("skipping tick — previous tick still in progress");
@@ -322,7 +332,16 @@ export function createPluginJobScheduler(
       if (dispatches.length > 0) {
         await Promise.allSettled(dispatches);
       }
+      databaseGuard.recordSuccess();
     } catch (err) {
+      if (
+        databaseGuard.handleError(
+          err,
+          "Pausing plugin job scheduler ticks because the database is currently unavailable",
+        )
+      ) {
+        return;
+      }
       log.error(
         { err: err instanceof Error ? err.message : String(err) },
         "scheduler tick error",