Navigate explorer back toward project

EXPLORER.md

@@ -82,9 +82,10 @@ writing are fixed scripts; the phone chooses only the path and the bytes.
 Same rule as `POST /sessions/{id}/cwd`, with the same wording, because where
 a relative path would be depends on something the reader cannot see. Every
 listing answers with `pwd -P` of the directory it listed, so the phone
-navigates on a resolved absolute path — the parent is a string operation on
-that, and a `~` the session was spawned with is shown as what it turned out
-to be. The phone never resolves `..` itself.
+navigates on a resolved absolute path. The phone also resolves `~` through the
+same route, then shortens that directory and every path beneath it back to
+tilde notation for display; it never guesses where a local or ssh user's home
+is. The phone never resolves `..` itself.
 
 ### 5. A read is capped and typed, and every state it can be in has a word
 
@@ -216,11 +217,13 @@ 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. From an open file, both the header's back button and Android back
 return to its containing directory. From a directory, the header's back button
-clears `files` and returns to the session, while Android back walks to the parent
-directory until the root and only then returns to the session. The `..` row
-remains as the visible, tappable form of the same directory movement. An editor
-with unsaved changes asks before either route discards them. "Back returns; it
-does not exit."
+clears `files` and returns to the session. Android back instead walks toward the
+session's project directory: upward to the common ancestor, then down one path
+segment per press, and at the project it returns to the session. This makes
+Back from `/etc` visibly travel through `/`, `/home`, and onward to a project
+under `~/repos`, rather than leading away from it. The `..` row remains explicit
+parent navigation. An editor with unsaved changes asks before either route
+discards them. "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