Move a session to another working directory

`POST /sessions/{id}/cwd`, behind a field in the session settings dialog. A
working directory is settled when the process is spawned -- the CLI is
launched with it as its cwd and there is no control request that changes one
-- so this records the new one and ends the process that is in the old one.
It does not start a replacement, and the field says so in a line beside it:
a session with no process starts on the next message or on Start, which is
this app's rule for that everywhere else, and "usually restarts" is a worse
control than "always stops".

The path is checked against the session's own machine and refused if it is
not there. The spawn path corrects instead of refusing, because it is
resuming a directory the *machine* recorded and that can be gone through
nobody's fault; a path somebody has just typed is different, and a mistyped
one accepted here would surface much later as a session that would not
start, with nothing pointing at the typo. The refusal names the machine and
the path, and is drawn under the field it is about.

Nothing of Claude Code's own is moved, and that is measured rather than
assumed: on CLI 2.1.237, `claude --resume <id>` finds a session from any
working directory -- an id that does not exist answers "No conversation
found with session ID", and a real one resumed from an unrelated directory
did not. So the conversation continues in the new place with nothing
relocated. Doing otherwise would mean reproducing a rule this app cannot
see the whole of; PLAN.md records what that rule is, for whoever tries.

Found while checking it: `SessionInfo.cwd` came from the snapshot a session
launched with, so a moved session went on reporting its *old* directory for
as long as its process lived -- a dialog showing a directory the next launch
would not use, with nothing saying so. It is read from the config where the
row is built now, the same way `setup_name` already was, and for the reason
already written above `setup_name`: only the manager holds the config, and
both of these change under a running session.

Checked end to end on the emulator against a session whose process really
does take a cwd: /proc said /tmp/cwd-a before and /tmp/cwd-b after, the
dialog showed the new path immediately rather than after a restart, and a
directory that is not there and a relative path were both refused with the
session left exactly as it was.

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

@@ -149,6 +149,14 @@ data class SessionSummary(
      * on when a backend is too old to say, which matches what that backend actually does.
      */
     val notify: Boolean,
+    /**
+     * The directory the session works in, or null where it was never given one.
+     *
+     * Null is not "the home directory": it is the session never having been told, and what the
+     * process then starts in belongs to whatever launches it. Shown as unset rather than filled in
+     * with a guess, so a reader changing it is choosing rather than confirming.
+     */
+    val cwd: String?,
     /**
      * How much context this session is holding, as the server last measured it -- see
      * `SessionEvent.UsageDelta`.
@@ -184,6 +192,7 @@ private fun parseSession(session: JSONObject) =
         permissionMode = session.optString("permissionMode").ifEmpty { null },
         imported = session.optBoolean("imported", false),
         notify = session.optBoolean("notify", true),
+        cwd = session.optString("cwd").ifEmpty { null },
         contextTokens =
             if (session.has("contextTokens")) session.getLong("contextTokens") else null,
         maxImageEdge = session.optInt("maxImageEdge", 0).takeIf { it > 0 },
@@ -509,6 +518,27 @@ fun unqueueMessage(settings: ServerSettings, sessionId: String, messageId: Strin
     ) {}
 }
 
+/**
+ * Moves a session to a different working directory.
+ *
+ * The server checks the directory is there on that machine and refuses if it is not -- a mistyped
+ * path accepted here would surface much later, as a session that would not start, with nothing
+ * pointing at the typo.
+ *
+ * Its process is **stopped**, because a working directory is settled when the process is spawned.
+ * The next thing said to the session starts it again in the new one, which is this app's rule for a
+ * session with no process everywhere else.
+ */
+fun setSessionCwd(settings: ServerSettings, sessionId: String, cwd: String) {
+    requestFromServer(
+        settings,
+        "/sessions/$sessionId/cwd",
+        method = "POST",
+        jsonBody = JSONObject().put("cwd", cwd).toString(),
+        readTimeoutMs = 30000,
+    ) {}
+}
+
 /** Uploads one picked image; the returned id goes into [sendMessage]. */
 fun uploadAttachment(
     settings: ServerSettings,

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

@@ -68,17 +68,53 @@ fun SessionSettingsDialog(
     // it, which is what not knowing looks like: distinguishable from off, and from a refusal.
     var notify by remember(sessionId) { mutableStateOf<Boolean?>(null) }
     var notifyError by remember { mutableStateOf<String?>(null) }
+    // Where the session works. Null until the server has been asked, for the same reason the
+    // switch above is: the row this dialog opened over is a snapshot, and a path drawn from it
+    // could be one somebody changed from another device. An empty answer is a session that was
+    // never given a directory, which is not the same as one whose directory is unknown -- the
+    // field is only enabled once one of those two is settled.
+    var cwd by remember(sessionId) { mutableStateOf<String?>(null) }
+    var typedCwd by remember(sessionId) { mutableStateOf("") }
+    var cwdError by remember { mutableStateOf<String?>(null) }
+    var movingCwd by remember { mutableStateOf(false) }
 
     LaunchedEffect(sessionId) {
-        notify =
+        try {
+            val fresh = withContext(Dispatchers.IO) { fetchSession(settings, sessionId) }
+            notify = fresh.notify
+            cwd = fresh.cwd.orEmpty()
+            typedCwd = fresh.cwd.orEmpty()
+        } catch (e: ApiException) {
+            // Left unknown rather than falling back to the stale row: the switch stays
+            // disabled, instead of offering a position nothing confirmed.
+            notifyError = e.message
+            notify = null
+        }
+    }
+
+    /**
+     * Moves the session, which ends the process that is in the old directory.
+     *
+     * Said plainly beside the field rather than confirmed in a second dialog: what it costs is a
+     * process, and a stopped session is a state this app already has a word and a button for.
+     */
+    fun moveCwd() {
+        val chosen = typedCwd.trim()
+        if (movingCwd || chosen.isEmpty() || chosen == cwd) return
+        movingCwd = true
+        cwdError = null
+        scope.launch {
             try {
-                withContext(Dispatchers.IO) { fetchSession(settings, sessionId).notify }
+                withContext(Dispatchers.IO) { setSessionCwd(settings, sessionId, chosen) }
+                cwd = chosen
             } catch (e: ApiException) {
-                // Left unknown rather than falling back to the stale row: the switch stays
-                // disabled, instead of offering a position nothing confirmed.
-                notifyError = e.message
-                null
+                // Where it happened: this field is the only thing on screen that knows a move was
+                // asked for, and the reason is usually the path itself.
+                cwdError = e.message
+            } finally {
+                movingCwd = false
             }
+        }
     }
 
     // Moved optimistically so the switch answers the finger that moved it, and put back if the
@@ -167,6 +203,53 @@ fun SessionSettingsDialog(
                         style = MaterialTheme.typography.bodySmall,
                     )
                 }
+                Spacer(Modifier.height(8.dp))
+                Row(
+                    verticalAlignment = Alignment.CenterVertically,
+                    modifier = Modifier.fillMaxWidth(),
+                ) {
+                    OutlinedTextField(
+                        value = typedCwd,
+                        onValueChange = { typedCwd = it },
+                        label = { Text("Working directory") },
+                        // What the field cannot say by being empty: a session that was never
+                        // given one starts wherever its launcher does, and this names that
+                        // rather than showing a path nobody chose.
+                        placeholder = { Text("wherever the session was started") },
+                        singleLine = true,
+                        enabled = cwd != null && !movingCwd,
+                        modifier = Modifier.weight(1f),
+                        keyboardOptions = KeyboardOptions(imeAction = ImeAction.Done),
+                        keyboardActions = KeyboardActions(onDone = { moveCwd() }),
+                    )
+                    TextButton(
+                        onClick = { moveCwd() },
+                        enabled =
+                            cwd != null &&
+                                !movingCwd &&
+                                typedCwd.trim().isNotEmpty() &&
+                                typedCwd.trim() != cwd,
+                    ) {
+                        Text(if (movingCwd) "Moving..." else "Move")
+                    }
+                }
+                // The whole of what pressing Move does, where it is about to be pressed. A
+                // directory is settled when the process is spawned, so there is no changing one
+                // under a running session -- it is ended, and the next thing said to the session
+                // starts it in the new place.
+                Text(
+                    "Moving stops the session's process. It starts again in the new directory " +
+                        "with the next message, or with Start.",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+                cwdError?.let {
+                    Text(
+                        it,
+                        color = MaterialTheme.colorScheme.error,
+                        style = MaterialTheme.typography.bodySmall,
+                    )
+                }
                 error?.let {
                     Spacer(Modifier.height(8.dp))
                     Text(