test(dashboard): cover isDashboardSnapshotEnabled default-on boundary

Pin undefined/empty/"true" to ON and exactly "false" to OFF so a
future edit cannot quietly regress to the old === "true" opt-in.

src/lib/dashboard/__tests__/snapshot-flag.test.ts

@@ -0,0 +1,43 @@
+/**
+ * v1.7.2 — unit tests for `isDashboardSnapshotEnabled`.
+ *
+ * The flag flipped default-ON in v1.7.2: the dashboard reads the unified
+ * `/api/dashboard/snapshot` cell UNLESS `NEXT_PUBLIC_DASHBOARD_SNAPSHOT`
+ * is exactly `"false"`. Pin the boundary so a future edit can't quietly
+ * regress to the old `=== "true"` opt-in semantics.
+ */
+import { describe, it, expect, afterEach } from "vitest";
+
+import { isDashboardSnapshotEnabled } from "../snapshot-flag";
+
+describe("isDashboardSnapshotEnabled", () => {
+  const original = process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT;
+
+  afterEach(() => {
+    if (original === undefined) {
+      delete process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT;
+    } else {
+      process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT = original;
+    }
+  });
+
+  it("defaults ON when the var is unset", () => {
+    delete process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT;
+    expect(isDashboardSnapshotEnabled()).toBe(true);
+  });
+
+  it("stays ON for an empty string", () => {
+    process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT = "";
+    expect(isDashboardSnapshotEnabled()).toBe(true);
+  });
+
+  it("turns OFF only for the exact string \"false\"", () => {
+    process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT = "false";
+    expect(isDashboardSnapshotEnabled()).toBe(false);
+  });
+
+  it('stays ON for "true"', () => {
+    process.env.NEXT_PUBLIC_DASHBOARD_SNAPSHOT = "true";
+    expect(isDashboardSnapshotEnabled()).toBe(true);
+  });
+});