content adapter: Site.GetPage without fully qualified path cannot find page

Given that page /s2/p2 was created by a content adapter:

{{ (site.GetPage "/s2/p2").Title }} --> p2  (pass)
{{ (site.GetPage "p2").Title }}     --> ""  (fail)

In comparison, when /s1/p1 is backed by a file:

{{ (site.GetPage "/s1/p1").Title }} --> p1  (pass)
{{ (site.GetPage "p1").Title }}     --> p1  (pass)

Test case:

func TestFoo(t *testing.T) {
    t.Parallel()

    files := `
-- hugo.toml --
disableKinds = ['rss','section','sitemap','taxonomy','term']
-- layouts/index.html --
Test A: {{ (site.GetPage "/s1/p1").Title }}
Test B: {{ (site.GetPage "p1").Title }}
Test C: {{ (site.GetPage "/s2/p2").Title }}
Test D: {{ (site.GetPage "p2").Title }}
-- layouts/_default/single.html --
{{ .Title }}
-- content/s1/p1.md --
---
title: p1
---
-- content/s2/_content.gotmpl --
{{ .AddPage (dict "path" "p2" "title" "p2") }}
`

    b := hugolib.Test(t, files)

    b.AssertFileExists("public/s1/p1/index.html", true)
    b.AssertFileExists("public/s2/p2/index.html", true)
    b.AssertFileContent("public/index.html",
        "Test A: p1",
        "Test B: p1",
        "Test C: p2",
        "Test D: p2", // fails
    )
}

Reference: https://discourse.gohugo.io/t/site-getpage-does-not-get-pages-created-with-an-adapter/50099/

gohugoio / hugo

content adapter: Site.GetPage without fully qualified path cannot find page #12561