A build that runs no commands refuses a word that is not a builtin, and says so

Board and web have no spawn. An unknown word there used to fall through to the command path and do nothing visible; now it answers with a failure the caller sees.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 7f2e0e1f..bf3ed1f0 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -556,6 +556,12 @@ pub fn executeFrom(p: *Pardes, id: usize, txt: []const u8, from_body: bool) ?usi
 /// A pane reused keeps what it showed: the new command runs below a line
 /// naming it, as acme appends to +Errors and never clears it (util.c:213).
 fn runCommand(p: *Pardes, from: usize, line: []const u8) ?usize {
+    // The board and the web page start no processes: a command pane there
+    // would say running for ever, and fill the slots.
+    if (comptime !hosted) {
+        p.reportFailure(from, "exec: not a builtin, and this build runs no commands");
+        return null;
+    }
     if (line.len > command_max) {
         p.reportFailure(from, "exec: a command line is at most 1024 bytes");
         return null;