A command of several lines keeps its pane's tag to one row, and the tag never panics on a longer prefix

A two-line exec made a command pane whose tag prefix held the line's newline,
so the tag ran to a second row and tagTintRange sliced its first row past its
end: panic. acme runs a multi-line selection as one command, and so does
pardes; the tag now shows the line's first row, cut at a character's start,
and '...', tagTintRange stays inside the row it is given, and the '% line'
echo turns the line's newlines into the terminal's, so it does not
staircase.

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

1 files changed, 8 insertions, 1 deletions

diff --git a/src/tagline.zig b/src/tagline.zig
index 14bf5677..28dffa06 100644
--- a/src/tagline.zig
+++ b/src/tagline.zig
@@ -112,8 +112,15 @@ pub fn pathPrefix(arena: std.mem.Allocator, pane: *Pane) ![]const u8 {
         return std.fmt.allocPrint(arena, "{s} [{d}/{d}]", .{ pv.path, pv.page + 1, pv.page_count });
     if (pane.image) |*state| return panes.Image.tagPrefix(arena, state);
     // A command pane: its directory, the line it runs, and how that went.
+    // Its first line only, cut to 48 bytes at a character's start: a tag's
+    // first row is where the prefix ends, and a line that ran over to a
+    // second (acme runs a multi-line selection as one command) would move
+    // it (body_layer.zig tagTintRange).
     if (pane.command) |line| {
-        const shown = line[0..@min(line.len, 48)];
+        const first = line[0 .. std.mem.indexOfAny(u8, line, "\r\n") orelse line.len];
+        var cut = @min(first.len, 48);
+        while (cut < first.len and cut > 0 and first[cut] & 0xC0 == 0x80) cut -= 1;
+        const shown = first[0..cut];
         const more = if (shown.len < line.len) "..." else "";
         var idbuf: [48]u8 = undefined;
         const id = exec.replId(&idbuf, pane);