A builtin or setting this build lacks is refused GUI-only, from an exec too

On a terminal, Fonts written to an exec was no builtin there, so it ran as a shell command and ended exit 127; ctl said unknown control message. Both now say Fonts is GUI-only, invalid here (a builtin another platform's build has, not in this build).

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

1 files changed, 8 insertions, 0 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 9ec6a426..cf4e01ab 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -657,6 +657,14 @@ pub fn executeFrom(p: *Pardes, id: usize, txt: []const u8, from_body: bool) ?usi
         .sent => |to| return to,
         .asked => return null,
     };
+    // A builtin or setting this build lacks (Fonts on a terminal) is said,
+    // never run as a shell command.
+    const word = cmd[0 .. std.mem.indexOfAny(u8, cmd, " \t") orelse cmd.len];
+    if (builtins.absentWhy(word) orelse if (config.Runtime.find(word) != null) @as([]const u8, "GUI-only") else null) |why| {
+        var said: [96]u8 = undefined;
+        p.reportFailure(id, std.fmt.bufPrint(&said, "{s} is {s}, invalid here", .{ word, why }) catch "GUI-only, invalid here");
+        return null;
+    }
     if (!takesCommandLine(p, id)) return runCommand(p, id, cmd);
     panes.Terminal.padOutputBelowEdits(p, id);
     panes.Terminal.noteCommand(pane, cmd);