An answer the question does not offer is refused, and the question stands

`answer z` to a question offering a and b succeeded, sent nothing and
dropped the question; so did Del's `answer x`. The ctl now takes only an
offered choice or -, refuses anything else with the choices it takes
(`answer takes k j or -`), and leaves the question asked.

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

1 files changed, 8 insertions, 3 deletions

diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index b4144fd2..c8be3bad 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -516,10 +516,15 @@ pub fn writePane(p: *Pardes, req: Req, pane: *Pane) Reply {
             } else if (std.mem.startsWith(u8, line, "answer ")) {
                 // The pane's question (its `ask` in the log), answered.
                 const choice = std.mem.trim(u8, line["answer ".len..], " ");
-                if (choice.len != 1) return refuse(p, req, "answer takes one choice, or -", line);
                 const id = p.paneBySerial(serial).?;
-                if (p.panes[id].?.prompt != .del_side and p.panes[id].?.prompt != .repl_choice)
-                    return refuse(p, req, "no question asked", line);
+                var offered: [64]u8 = undefined;
+                const choices = p.questionChoices(id, &offered) orelse return refuse(p, req, "no question asked", line);
+                // Only a choice the question offers answers it; anything
+                // else leaves it standing, and says what it takes.
+                if (!std.mem.eql(u8, choice, "-") and (choice.len != 1 or std.mem.indexOfScalar(u8, choices, choice[0]) == null)) {
+                    var why: [96]u8 = undefined;
+                    return refuse(p, req, std.fmt.bufPrint(&why, "answer takes {s} or -", .{choices}) catch "answer takes a choice or -", line);
+                }
                 if (apply) _ = p.answerQuestion(id, if (choice[0] == '-') null else choice[0]);
             } else if (!apply) {
                 if (checkBuiltin(p, req, line, .pane)) |refusal| return refusal;