chore(perf): prepare database post-GC capture

apps/electron-backend-e2e/src/performance/database-worker-post-gc-selection.ts

@@ -0,0 +1,70 @@
+export type DatabaseWorkerPostGcUnavailableReason =
+    | 'database-worker-missing'
+    | 'database-worker-not-idle'
+    | 'multiple-database-workers';
+
+export interface DatabaseWorkerPostGcSelectionRecord {
+    readonly captureGeneration: number | null;
+    readonly kind: string;
+    readonly ordinal: number;
+    readonly pendingCount: number;
+}
+
+export interface DatabaseWorkerPostGcSelection<T> {
+    readonly selected: T | null;
+    readonly unavailableReason: DatabaseWorkerPostGcUnavailableReason | null;
+}
+
+export interface DatabaseWorkerPostGcSelectionApi {
+    select<T extends DatabaseWorkerPostGcSelectionRecord>(
+        records: readonly T[],
+        activeGeneration: number
+    ): DatabaseWorkerPostGcSelection<T>;
+}
+
+export function createDatabaseWorkerPostGcSelectionApi(): DatabaseWorkerPostGcSelectionApi {
+    const helpers = {
+        select<T extends DatabaseWorkerPostGcSelectionRecord>(
+            records: readonly T[],
+            activeGeneration: number
+        ): DatabaseWorkerPostGcSelection<T> {
+            const currentDatabaseWorkers: T[] = [];
+            for (const record of records) {
+                if (
+                    record.captureGeneration === activeGeneration &&
+                    record.kind === 'database.worker'
+                ) {
+                    currentDatabaseWorkers.push(record);
+                }
+            }
+
+            if (currentDatabaseWorkers.length === 0) {
+                return Object.freeze({
+                    selected: null,
+                    unavailableReason: 'database-worker-missing',
+                });
+            }
+            if (currentDatabaseWorkers.length > 1) {
+                return Object.freeze({
+                    selected: null,
+                    unavailableReason: 'multiple-database-workers',
+                });
+            }
+
+            const selected = currentDatabaseWorkers[0] as T;
+            if (selected.pendingCount > 0) {
+                return Object.freeze({
+                    selected: null,
+                    unavailableReason: 'database-worker-not-idle',
+                });
+            }
+
+            return Object.freeze({
+                selected,
+                unavailableReason: null,
+            });
+        },
+    };
+
+    return Object.freeze({ select: helpers.select });
+}