Return from files to explorer

EXPLORER.md

@@ -214,11 +214,11 @@ be lost. The explorer draws over the session, which deliberately has no
 `FilesScreen` is composed **on top of** the session in the same `Box`, and
 the session stays composed under it: its event stream keeps flowing, its
 scroll position and draft stay where they were, and returning from a file
-costs nothing. Back — the button and the platform gesture — clears `files`
-and returns to the session from anywhere in the explorer. Directory navigation
-stays in the listing: `..` is an explicit row rather than a hidden second
-meaning for Back. An editor with unsaved changes asks before closing. "Back
-returns; it does not exit."
+costs nothing. Back — the button and the platform gesture — returns from an
+open file to its containing directory, then clears `files` and returns to the
+session. Directory navigation stays in the listing: `..` is an explicit row
+rather than a hidden second meaning for Back. An editor with unsaved changes
+asks before returning to the directory. "Back returns; it does not exit."
 
 Rejected: a `Screen.Files` beside `Screen.Session`. Every route back from a
 leaf screen goes to Main today, and a session disposed and re-created on each