Undo and Redo are builtins, as in acme's tags, so a pane's ctl and exec can step its body

Over 9P there was no way to take back an edit: acme's Undo and Redo were keys only. They are now pane builtins, reached from a tag, a pane ctl and exec, and listed in /commands. They are not added to the default tags, which would change every tag.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index 23d853c8..a755969b 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -850,6 +850,20 @@ pub const Togglettymode = struct {
     }
 };
 
+/// acme's Undo and Redo (exec.c `undo`): step the pane's body back or
+/// forward through its edits, from a tag, a pane ctl or exec.
+pub const Undo = struct {
+    pub fn run(c: Ctx) void {
+        edit.doUndo(c.p, &c.pane.body);
+    }
+};
+
+pub const Redo = struct {
+    pub fn run(c: Ctx) void {
+        edit.doRedo(c.p, &c.pane.body);
+    }
+};
+
 /// Fold a pane to its tag, or restore its share of the column.
 pub const Collapse = struct {
     pub fn run(c: Ctx) void {