What exactly does Observation track: computed properties, ignored properties, collections, nested objects and equal writes?

Predict first

Which of these changes notify a tracking scope?

import Observation

@Observable final class Cart {
    var items: [String] = ["a"]
    var discount = 0
    @ObservationIgnored var hits = 0
    var count: Int { items.count }
    var label: String { "\(count) items" }
    var note = Note()
}
@Observable final class Note { var text = "x" }
final class Plain { var text = "x" }
@Observable final class Holder { var plain = Plain() }

func fires(_ read: () -> Void, then change: () -> Void) -> Bool {
    nonisolated(unsafe) var fired = false
    withObservationTracking(read, onChange: { fired = true })
    change()
    return fired
}
let c = Cart()
print("read count, append item:", fires({ _ = c.count }, then: { c.items.append("b") }))
print("read count, change discount:", fires({ _ = c.count }, then: { c.discount = 5 }))
print("read computed label, append:", fires({ _ = c.label }, then: { c.items.append("c") }))
print("read items, change @ObservationIgnored:", fires({ _ = c.items }, then: { c.hits += 1 }))
print("read items.count, replace an element:", fires({ _ = c.items.count }, then: { c.items[0] = "z" }))
let later = { _ = c.discount }
print("property read only inside a stored closure:", fires({ _ = later }, then: { c.discount = 9 }))
print("assign the same value:", fires({ _ = c.discount }, then: { c.discount = c.discount }))
print("nested @Observable, edit it:", fires({ _ = c.note.text }, then: { c.note.text = "y" }))
let h = Holder()
print("plain class inside, edit it:", fires({ _ = h.plain.text }, then: { h.plain.text = "y" }))
print("plain class inside, replace it:", fires({ _ = h.plain.text }, then: { h.plain = Plain() }))

• true false true false true false false true false true
• all true
• only the append and the nested edit