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`
+costs nothing. Back — the button and the platform gesture — returns from an
-and returns to the session from anywhere in the explorer. Directory navigation
+open file to its containing directory, then clears `files` and returns to the
-stays in the listing: `..` is an explicit row rather than a hidden second
+session. Directory navigation stays in the listing: `..` is an explicit row
-meaning for Back. An editor with unsaved changes asks before closing. "Back
+rather than a hidden second meaning for Back. An editor with unsaved changes
-returns; it does not exit."
+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

app/androidApp/src/main/kotlin/com/example/aiapp/FilesScreen.kt

@@ -54,15 +54,16 @@ data class FilesTarget(val setup: String, val setupName: String, val start: Stri
 private sealed class Spot(val path: String) {
     class Dir(path: String) : Spot(path)
 
-    class Doc(path: String) : Spot(path)
+    class Doc(path: String, val directory: Dir) : Spot(path)
 }
 
 /**
  * The files on the machine a session runs on: browse them, read one, change one.
  *
  * Drawn **over** the session rather than instead of it (see [AppRoot]), so its event stream keeps
- * flowing and coming back from a file costs nothing. Back always closes the explorer and returns to
+ * flowing and coming back from a file costs nothing. Back from a file returns to its directory;
- * that session; directory navigation stays inside the listing, where its `..` row is explicit.
+ * back from a directory closes the explorer and returns to the session. Directory navigation stays
+ * inside the listing, where its `..` row is explicit.
  *
  * Every directory that has been visited is kept for as long as this is open; the refresh glyph is
  * how one gets asked again on purpose, and creating something refetches the directory it was
@@ -88,7 +89,11 @@ fun FilesScreen(settings: ServerSettings, target: FilesTarget, onClose: () -> Un
     }
 
     fun back() {
-        if (editing && dirty) askUnsaved = true else onClose()
+        when {
+            editing && dirty -> askUnsaved = true
+            here is Spot.Doc -> go((here as Spot.Doc).directory)
+            else -> onClose()
+        }
     }
 
     suspend fun load(path: String, again: Boolean) {
@@ -140,7 +145,7 @@ fun FilesScreen(settings: ServerSettings, target: FilesTarget, onClose: () -> Un
                         )
                     }
                     LaunchedEffect(spot.path) { load(spot.path, again = false) }
-                    DirectoryBody(state, onOpen = ::go)
+                    DirectoryBody(state, directory = spot, onOpen = ::go)
                 }
                 is Spot.Doc ->
                     DocPane(
@@ -161,7 +166,8 @@ fun FilesScreen(settings: ServerSettings, target: FilesTarget, onClose: () -> Un
         UnsavedDialog(
             onDiscard = {
                 askUnsaved = false
-                onClose()
+                val spot = here
+                if (spot is Spot.Doc) go(spot.directory) else onClose()
             },
             onCancel = { askUnsaved = false },
         )
@@ -183,7 +189,7 @@ fun FilesScreen(settings: ServerSettings, target: FilesTarget, onClose: () -> Un
                     load(dir.path, again = true)
                     // A new file has nothing to look at, so it opens where it can be filled in.
                     if (!isDirectory) {
-                        go(Spot.Doc(path))
+                        go(Spot.Doc(path, dir))
                         editing = true
                     }
                 }
@@ -235,7 +241,11 @@ private fun FilesHeader(
  * looks like a right one.
  */
 @Composable
-private fun ColumnScope.DirectoryBody(state: LoadState<Listing>, onOpen: (Spot) -> Unit) {
+private fun ColumnScope.DirectoryBody(
+    state: LoadState<Listing>,
+    directory: Spot.Dir,
+    onOpen: (Spot) -> Unit,
+) {
     when (state) {
         is LoadState.Loading -> CircularProgressIndicator(Modifier.padding(16.dp))
         is LoadState.Error ->
@@ -276,7 +286,9 @@ private fun ColumnScope.DirectoryBody(state: LoadState<Listing>, onOpen: (Spot)
                         name = entry.name,
                         trailing = trailingOf(entry),
                         onClick = {
-                            onOpen(if (entry.isDirectory) Spot.Dir(path) else Spot.Doc(path))
+                            onOpen(
+                                if (entry.isDirectory) Spot.Dir(path) else Spot.Doc(path, directory)
+                            )
                         },
                     )
                 }