A replace through data or body, truncate then write, is one undo step

A shell's printf x > data truncates the addressed range and then writes, and each pushed its own undo point, so one replace took two Undos. A truncation of data, xdata or body now lets the write that follows it at once join its step, as acme's replace is one.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/src/fs.zig b/src/fs.zig
index 42d761ca..0a4473d6 100644
--- a/src/fs.zig
+++ b/src/fs.zig
@@ -598,7 +598,8 @@ test "virtual body writes can read their input from the same pane" {
     const path = try std.fmt.bufPrint(&path_buffer, "/virtual/pane/{d}/body", .{pane.serial});
     try write(p, path, pane.file.?.content);
     try std.testing.expectEqualStrings("same pane contents\n", pane.file.?.content);
-    try std.testing.expectEqual(@as(usize, 2), pane.file.?.history.undo_len);
+    // The truncation and the write are one undo step.
+    try std.testing.expectEqual(@as(usize, 1), pane.file.?.history.undo_len);
     const events = &p.panes[p.active].?.fs.events;
     try std.testing.expect(std.mem.startsWith(u8, events.peek().?, "ED"));
     events.pop();