feat(FN-5430): gate task update invalidation in scheduler

Scheduler now gates task update invalidation, preventing spurious invalidations when engine lifecycle changes (soft-delete, lease recovery) touch task metadata, with coverage via new scheduler invalidation tests and a small dashboard server test adjustment.

Fusion-Task-Id: FN-5430

packages/engine/src/scheduler.ts

@@ -87,6 +87,20 @@ function isIgnoredOverlapPath(path: string, ignorePath: string): boolean {
   return normalizedPath === normalizedIgnore || normalizedPath.startsWith(`${normalizedIgnore}/`);
 }
 
+function computeAutoClaimFingerprint(task: Task): string {
+  const dependencies = [...(task.dependencies ?? [])].sort().join(",");
+  const sortAt = task.columnMovedAt ?? task.createdAt;
+  return [
+    task.column,
+    task.paused === true ? "1" : "0",
+    task.assignedAgentId ?? "",
+    task.checkedOutBy ?? "",
+    task.deletedAt ?? "",
+    dependencies,
+    sortAt,
+  ].join("|");
+}
+
 /**
  * Remove scope entries that match configured overlap-ignore paths.
  * Used by scheduler overlap gating so shared safe paths (docs/generated/etc.)
@@ -320,6 +334,8 @@ export class Scheduler {
   private wasPermanentAgentUnavailable = new Set<string>();
   /** Tracks dispatch-queued reason signatures to avoid per-tick log spam. */
   private wasDispatchQueuedReasonLogged = new Set<string>();
+  /** Tracks per-task candidacy fingerprints for task:updated auto-claim invalidation gating. */
+  private lastAutoClaimFingerprint = new Map<string, string>();
   private readonly staleTaskReporter: StaleTaskReporter;
   private readonly backlogPressureReporter: BacklogPressureReporter;
   private lastStaleTaskReportAt = 0;
@@ -348,7 +364,8 @@ export class Scheduler {
      * pass immediately instead of waiting for the next poll interval.
      * This reduces latency from up to 15 seconds to near-instant.
      */
-    this.store.on("task:created", () => {
+    this.store.on("task:created", (task) => {
+      this.lastAutoClaimFingerprint.set(task.id, computeAutoClaimFingerprint(task));
       this.options.snapshotManager?.invalidate("task:created");
       schedulerLog.log("Task created — triggering scheduling");
       this.schedule();
@@ -389,6 +406,7 @@ export class Scheduler {
      * update feature status and potentially activate next pending slice.
      */
     this.store.on("task:moved", async ({ task, from, to }) => {
+      this.lastAutoClaimFingerprint.set(task.id, computeAutoClaimFingerprint(task));
       if (from === "todo" || to === "todo") {
         this.options.snapshotManager?.invalidate(`task:moved:${from}->${to}`);
       }
@@ -502,7 +520,12 @@ export class Scheduler {
      * Also detects task-level unpause transitions and triggers immediate scheduling.
      */
     this.store.on("task:updated", (task) => {
-      this.options.snapshotManager?.invalidate("task:updated");
+      const nextFingerprint = computeAutoClaimFingerprint(task);
+      const previousFingerprint = this.lastAutoClaimFingerprint.get(task.id);
+      if (!previousFingerprint || previousFingerprint !== nextFingerprint) {
+        this.lastAutoClaimFingerprint.set(task.id, nextFingerprint);
+        this.options.snapshotManager?.invalidate("task:updated");
+      }
       // Track mission failure signals before moveTask clears failure metadata.
       if (task.sliceId && task.column === "in-progress" && task.status === "failed") {
         this.failedTaskIds.add(task.id);
@@ -543,6 +566,7 @@ export class Scheduler {
     });
 
     this.store.on("task:deleted", (task) => {
+      this.lastAutoClaimFingerprint.delete(task.id);
       this.options.snapshotManager?.invalidate("task:deleted");
       this.pausedTaskIds.delete(task.id);
       this.failedTaskIds.delete(task.id);