fix(FN-4401): address snapshot review feedback

Fusion-Task-Id: FN-4401
Fusion-Task-Lineage: c1b6c497-b22c-48d5-b1c8-299877bf09ac

packages/engine/src/__tests__/auto-claim-snapshot.test.ts

@@ -1,8 +1,8 @@
 import { describe, expect, it, vi } from "vitest";
-import type { TaskDetail } from "@fusion/core";
+import type { Task } from "@fusion/core";
 import { AutoClaimSnapshotManager, extractDescriptionFirstLine } from "../auto-claim-snapshot.js";
 
-function makeTask(overrides: Partial<TaskDetail> & Pick<TaskDetail, "id">): TaskDetail {
+function makeTask(overrides: Partial<Task> & Pick<Task, "id">): Task {
   return {
     id: overrides.id,
     title: overrides.title ?? null,
@@ -20,7 +20,7 @@ function makeTask(overrides: Partial<TaskDetail> & Pick<TaskDetail, "id">): Task
     checkedOutBy: overrides.checkedOutBy,
     paused: overrides.paused,
     columnMovedAt: overrides.columnMovedAt,
-  } as TaskDetail;
+  } as Task;
 }
 
 describe("AutoClaimSnapshotManager", () => {
@@ -87,6 +87,22 @@ describe("AutoClaimSnapshotManager", () => {
     expect(snapshot.tasks.map((t) => t.id)).toEqual(["FN-1", "FN-2", "FN-3"]);
   });
 
+  it("caps candidate set to 50 and computes capped baseScore", async () => {
+    const tasks = Array.from({ length: 55 }, (_, idx) => makeTask({
+      id: `FN-${idx + 1}`,
+      createdAt: "2025-12-01T00:00:00.000Z",
+    }));
+    const manager = new AutoClaimSnapshotManager({
+      taskStore: { listTasks: vi.fn(async () => tasks) },
+      now: () => Date.parse("2026-01-03T00:00:00.000Z"),
+    });
+
+    const snapshot = await manager.getSnapshot();
+
+    expect(snapshot.tasks).toHaveLength(50);
+    expect(snapshot.tasks[0]?.baseScore).toBe(5);
+  });
+
   it("extracts first non-empty description line and caps length", () => {
     expect(extractDescriptionFirstLine("\n\nfirst line\nsecond line")).toBe("first line");
     expect(extractDescriptionFirstLine("   \n\t\n")).toBe("");

packages/engine/src/auto-claim-snapshot.ts

@@ -1,4 +1,4 @@
-import type { TaskDetail, TaskStore } from "@fusion/core";
+import type { Task, TaskStore } from "@fusion/core";
 import { createLogger, type Logger } from "./logger.js";
 
 /**
@@ -13,7 +13,7 @@ export interface AutoClaimCandidate {
   createdAt: string;
   columnMovedAt?: string;
   baseScore: number;
-  column: TaskDetail["column"];
+  column: Task["column"];
 }
 
 export interface AutoClaimSnapshot {
@@ -37,6 +37,7 @@ export class AutoClaimSnapshotManager {
   private readonly now: () => number;
   private cache: AutoClaimSnapshot | null = null;
   private staleReason: "ttl" | "invalidate" = "ttl";
+  private invalidatedAt = 0;
   private inFlight: Promise<AutoClaimSnapshot> | null = null;
 
   constructor({ taskStore, ttlMs = 30_000, logger = autoClaimSnapshotLog, now = Date.now }: AutoClaimSnapshotManagerOptions) {
@@ -49,6 +50,7 @@ export class AutoClaimSnapshotManager {
   invalidate(reason: string): void {
     this.cache = null;
     this.staleReason = "invalidate";
+    this.invalidatedAt = this.now();
     this.logger.log(`invalidate reason=${reason}`);
   }
 
@@ -61,10 +63,12 @@ export class AutoClaimSnapshotManager {
       return this.inFlight;
     }
 
+    const startedAt = this.now();
     this.inFlight = this.rebuild();
     try {
       const next = await this.inFlight;
-      this.cache = next;
+      const invalidatedDuringRebuild = this.invalidatedAt > startedAt;
+      this.cache = invalidatedDuringRebuild ? null : next;
       return next;
     } finally {
       this.inFlight = null;
@@ -105,7 +109,7 @@ export class AutoClaimSnapshotManager {
     return snapshot;
   }
 
-  private toCandidate(task: TaskDetail, now: number): AutoClaimCandidate {
+  private toCandidate(task: Task, now: number): AutoClaimCandidate {
     const reference = task.columnMovedAt ?? task.createdAt;
     const ageMs = Math.max(0, now - Date.parse(reference));
     const ageHours = ageMs / (1000 * 60 * 60);