Fix explorer back and session usage selection

EXPLORER.md

@@ -215,9 +215,9 @@ be lost. The explorer draws over the session, which deliberately has no
 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`
-when set and goes to the list otherwise. Inside the explorer the same back
-steps one level: editor → viewer (with the unsaved question) → listing →
-parent directory, and only from the starting directory does it close. "Back
+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."
 
 Rejected: a `Screen.Files` beside `Screen.Session`. Every route back from a