test(a11y): cover delayed and interrupted Map Source focus

Keep the Esri settlement assertion exact, verify selected-source focus and Tab departure in Chromium, cancel pending work during disposal, and document the focused behavior.

CHANGELOG.md

@@ -15,6 +15,10 @@ of current runtime behavior, see [`docs/CURRENT-STATE.md`](docs/CURRENT-STATE.md
 
 ### Fixed
 
+- Map Source keyboard opening retries focus until the selected tile is visible.
+  Leaving the disclosure, pointer interaction, or closing the tray cancels the
+  pending handoff so delayed work cannot pull focus back.
+
 - Scope, Bloom, Sharpen, location search and generated style sliders expose
   explicit accessible names. The first-run checkbox retains its native label.
 - FIRMS records a source as successful only after appending its rows, avoiding