A pane tag wraps onto rows and can collapse to one, as acme's does

acme's frame wraps a tag at its right edge and the window grows to show
every row (wind.c wintaglines); Tagup/Tagdown shrink it to one row and back.
Pane tags used to be one row, scrolled sideways to the caret. Now a tag's
lines wrap at its width (one cell kept for the caret past a full row) and it
starts expanded; insert-mode Up on the first row collapses it, Down on the
last row expands it, and Alt-Up/Alt-Down do so in either mode. A word the
wrap breaks across rows is still one word to a click and a selection.
Column and workspace tags keep scrolling sideways.

Tests read body rows relative to the body's first row; the 41 snapshot
goldens that moved were re-recorded by name after a programmatic check that
each differs only by body rows shifting under the taller tags, and twelve
scripts whose clicks targeted fixed rows now click the same text.

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

1 files changed, 5 insertions, 0 deletions

diff --git a/src/panes.zig b/src/panes.zig
index e4621311..b812b310 100644
--- a/src/panes.zig
+++ b/src/panes.zig
@@ -186,6 +186,11 @@ pub const Pane = struct {
     /// scrolls to keep its caret in view while it has the keyboard; pointer
     /// rows count from this line, not the tag's first.
     tag_top: u16 = 0,
+    /// The tag shows all its rows (acme's `tagexpand`, on by default); off,
+    /// one row, as acme's Tagup leaves it. Down on the
+    /// tag's last line and Up on its first, typing, or Alt-Down and Alt-Up
+    /// in the tag, as acme's arrows in a tag (plan9port text.c:776).
+    tag_expanded: bool = true,
     /// How long the tag's computed prefix was when its positions were last
     /// placed. They count from the start of the prefix, so when it grows or
     /// shrinks (a rename, the dirty marker, a PDF's page) what follows it