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, 3 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 1b82d2a8..84a0ad5f 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -534,9 +534,14 @@ fn runCommand(p: *Pardes, from: usize, line: []const u8) ?usize {
         // shown, then a soft reset (DECSTR) for the rest.
         if (panes.Terminal.onAlternateScreen(pane)) panes.Terminal.feedOutput(p, pane, "\x1b[?1049l");
         panes.Terminal.feedOutput(p, pane, "\x1b[?1000l\x1b[?1002l\x1b[?1003l\x1b[?1006l\x1b[?2004l\x1b[?25h\x1b[!p");
-        var buf: [command_max + 8]u8 = undefined;
-        const lead = if (panes.Terminal.gridCursor(pane).x != 0) "\r\n" else "";
-        panes.Terminal.feedOutput(p, pane, std.fmt.bufPrint(&buf, "{s}% {s}\r\n", .{ lead, line }) catch "%\r\n");
+        // The line as it runs, its newlines the terminal's, so a multi-line
+        // command does not staircase.
+        var buf: [2 * command_max + 8]u8 = undefined;
+        var w = std.Io.Writer.fixed(&buf);
+        w.writeAll(if (panes.Terminal.gridCursor(pane).x != 0) "\r\n% " else "% ") catch {};
+        for (line) |c| (if (c == '\n') w.writeAll("\r\n") else w.writeByte(c)) catch {};
+        w.writeAll("\r\n") catch {};
+        panes.Terminal.feedOutput(p, pane, w.buffered());
         p.emit(.{ .spawn = .{ .pane = @intCast(id), .serial = pane.serial, .cwd = .from(pane.cwdSlice()) } });
         noteRun(p, pane, "run", line);
         return id;