The writes of one open of data, body or xdata are one undo step

bash line-buffers its stdout, so printf 'x\ny\nz\n' > data arrives as three writes and took three Undos. A write now leaves the join mark a truncation already left, so the next write on the file joins its step until the open is released; a truncation and any other edit start a step of their own.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/src/ninep/tree.zig b/src/ninep/tree.zig
index 64089c01..a8b86a96 100644
--- a/src/ninep/tree.zig
+++ b/src/ninep/tree.zig
@@ -831,6 +831,10 @@ fn releaseHandle(p: *Pardes, req: Req) void {
         p.panes[id].?.fs.tag_rewrite = false;
         p.panes[id].?.fs.tag_held_newline = false;
     };
+    // The writes of one open are one undo step (pane.zig `joined`).
+    if (t == .pane and (t.pane.file == .body or t.pane.file == .data or t.pane.file == .xdata)) if (p.paneBySerial(t.pane.serial)) |id| {
+        p.panes[id].?.fs.joined = null;
+    };
     // `: > limit` clears it for good once its open goes.
     if (t == .pane and t.pane.file == .limit) if (p.paneBySerial(t.pane.serial)) |id| {
         p.panes[id].?.fs.limit_truncated = null;