fix: alert again when a change watch returns to a seen page

apps/server/src/engine/service.ts

@@ -1062,11 +1062,11 @@ export class AgentService {
           : this.matchesPrice(text, Number(monitor.value));
     const previouslyMatched = Boolean(task.state.matched);
     const shouldNotify = matched && (monitor.condition === "change" || !previouslyMatched);
-    // A condition becoming true again is a new event, even with identical page text.
-    // Commit its sequence with the outcome so publication retries still deduplicate.
-    const alertSequence =
-      Number(task.state.alertSequence ?? 0) +
-      (shouldNotify && monitor.condition !== "change" ? 1 : 0);
+    // A notification-worthy observation is a new event, even when the page text is
+    // identical to an earlier one (a change back to a seen state, or a condition that
+    // cleared and reappeared). Commit its sequence with the outcome so publication
+    // retries still deduplicate on the same saved notice key.
+    const alertSequence = Number(task.state.alertSequence ?? 0) + (shouldNotify ? 1 : 0);
     const nextCheckAt = new Date(Date.now() + monitor.intervalMinutes * 60000).toISOString();
     await ctx.guard();
     // Worker lease is checked before each publication; monitor control also invalidates that lease.
@@ -1112,10 +1112,7 @@ export class AgentService {
           ? {
               title: monitor.title,
               body: `Condition met at ${observation.url}: ${text.slice(0, 240)}`,
-              key:
-                monitor.condition === "change"
-                  ? `monitor:${monitor.id}:${currentHash}`
-                  : `monitor:${monitor.id}:${alertSequence}:${currentHash}`,
+              key: `monitor:${monitor.id}:${alertSequence}:${currentHash}`,
             }
           : null,
       },

tests/agent-api.test.ts

@@ -296,7 +296,9 @@ test("sample monitor saves its baseline and deduplicates notifications for repea
     await server.agent.worker.tick();
   }
   const found = await notifications();
-  assert.equal(found.length, 2);
+  // Identical repeats stay quiet; the final flip back to a previously seen
+  // page is a new change event and alerts again.
+  assert.equal(found.length, 3);
   assert.ok(found.every((item) => !item.read));
   const readNotification = await read<AgentNotification>(`/notifications/${found[0].id}/read`, {});
   assert.equal(readNotification.read, true);

tests/monitor-recovery.test.ts

@@ -137,6 +137,12 @@ test("a page change stays alertable when the task outcome is lost after the base
 });
 
 for (const scenario of [
+  {
+    condition: "change",
+    value: "",
+    pages: ["Sold out", "Available now", "Sold out", "Available now"],
+    expectedAlerts: 3,
+  },
   {
     condition: "contains",
     value: "available now",