fix: harden desktop monitoring recovery

apps/desktop-client/src/main/monitor-scheduler.ts

@@ -64,6 +64,7 @@ interface MonitorSchedulerSelectionOptions {
   maxConcurrency: number
   activePlatforms: ReadonlySet<string>
   activeQuestionKeys: ReadonlySet<string>
+  blockedPlatforms?: ReadonlySet<string>
   activeCount: number
 }
 
@@ -434,6 +435,22 @@ export function noteMonitorTaskLeaseMiss(taskId: string): void {
   })
 }
 
+export function noteMonitorTaskDeferred(taskId: string, delayMs: number): void {
+  const now = Date.now()
+  const availableAt = now + Math.max(0, delayMs)
+
+  mutatePersistedState((draft) => {
+    const existing = draft.tasks[taskId]
+    if (!existing) {
+      return
+    }
+
+    existing.state = 'queued'
+    existing.availableAt = Math.max(existing.availableAt, availableAt)
+    existing.lastSeenAt = now
+  })
+}
+
 export function noteMonitorTaskCompleted(taskId: string): void {
   const now = Date.now()
 
@@ -488,6 +505,10 @@ export function selectNextMonitorTask(
     })
 
   for (const candidate of candidates) {
+    if (options.blockedPlatforms?.has(candidate.platform)) {
+      continue
+    }
+
     if (options.activePlatforms.has(candidate.platform)) {
       continue
     }