Keep same folder when opening new window.

src/Pane.zig

@@ -757,6 +757,10 @@ fn onContentFocus(ctx: ?*anyopaque) void {
 }
 
 fn onSplitClicked(_: *gtk.Button, self: *Pane) callconv(.c) void {
+    // The button belongs to this pane, which need not be the focused one: a
+    // header click does not move focus. Focusing it first makes the new
+    // terminal split this pane and start in this pane's directory.
+    self.view.setFocused(self);
     self.view.addPane(.plain(.terminal)) catch |err| {
         std.log.err("failed to open terminal: {s}", .{@errorName(err)});
     };

src/View.zig

@@ -302,7 +302,22 @@ pub fn addPane(self: *View, raw: Pane.Spec) !void {
     if (raw.kind() == .review and self.reviewPane() != null) {
         return error.ReviewAlreadyOpen;
     }
-    const spec = self.stamp(raw);
+
+    // A terminal opened without a directory of its own starts where the pane
+    // it splits is working, so a new shell beside a `cd`-ed one lands in the
+    // same place rather than back in $HOME. Only borrowed for the length of
+    // `Pane.create`, which spawns the shell before returning.
+    var dir_buf: [std.fs.max_path_bytes]u8 = undefined;
+    const inherited: Pane.Spec = switch (raw) {
+        .terminal => |opts| if (opts.cwd.len == 0 and opts.hc.len == 0) blk: {
+            const from = self.focusedPane() orelse break :blk raw;
+            var with_dir = opts;
+            with_dir.cwd = self.paneDirectory(from, &dir_buf);
+            break :blk .{ .terminal = with_dir };
+        } else raw,
+        else => raw,
+    };
+    const spec = self.stamp(inherited);
 
     const pane = try Pane.create(self.alloc, self, spec);
     errdefer pane.destroy();