Repair stale views after object-signal mutation

Understand the likely causes

• A signal’s default equality can consider the same object reference unchanged. Mutating an array with push and returning that same array can therefore leave computed consumers cached. A readonly signal view restricts which methods are exposed but does not recursively freeze the referenced object. Custom equality can suppress changes too.
• Manual detection or changing change-detection strategy can mask one visual symptom without fixing the reactive state relationship. Derived values should usually be computed from one authoritative source rather than copied into additional writable fields through effects.

Find the mutation that bypasses replacement

The contextual snippet below mutates the current array and returns the identical reference. It is intentionally marked non-runnable because it illustrates the unsupported update policy, not a recommended solution. Trace all writers, including shared aliases retained by services or callbacks. A view reading the raw array length during another event can show the mutation even while a computed total stays cached, making the defect look intermittent.

items.update(current => {
  current.push(3);
  return current;
});

Replace the changed value and retain pure derivation

The complete correction returns a new array and derives its total through computed. It records the previous reference only to verify that the update creates a replacement. The result confirms both the new aggregate and identity change in the real pinned Angular signal implementation. This is not a DOM or performance test. For nested records, replace the relevant changed objects as well and preserve stable entity identifiers for list rendering. Do not generate random row keys just to force a redraw.

import { computed, signal } from "@angular/core";
const items = signal<readonly number[]>([1, 2]);
const total = computed(() => items().reduce((sum, value) => sum + value, 0));
console.log(total());
const before = items();
items.update(current => [...current, 3]);
console.log(total(), before === items());

3
6 false

Review equality, ownership, and template reads

Verify that the template calls the signal getter, the update reaches the intended store instance, and no child provider created an accidental second owner. Review a custom equality function against the fields consumers actually use. If a mutation comes from HTTP, decode it and apply a documented transition rather than exposing every internal signal for arbitrary writes. OnPush still has supported notification paths; it is not a reason to scatter detectChanges calls through the feature.

Keep it from recurring

• Keep one authoritative source, expose explicit update commands, use immutable replacements, and test identity-sensitive transitions. Treat custom equality and manual change detection as reviewed design choices rather than routine fixes for stale state.