Shell refuses a name that is no executable, and bare restores the default

Shell took any word and the host quietly ran another shell at the next
spawn. It now refuses a path or name that is not executable ("Shell: x:
no executable by that name", failing a ctl write, logged err), a bare
Shell goes back to the default, and a default $SHELL that is not
executable falls back to /bin/sh. shellset's golden takes the refusal on
the message row (re-recorded by name).

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

1 files changed, 5 insertions, 3 deletions

diff --git a/src/config.zig b/src/config.zig
index a59fe18d..e0fcab48 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -350,7 +350,8 @@ test "wheel drift guard" {
 pub fn defaultShell() []const u8 {
     if (comptime pardes.hosted) if (std.c.getenv("SHELL")) |s| {
         const shell = std.mem.span(s);
-        if (shell.len > 0) return shell;
+        // One that is not there, or not executable, is no shell: /bin/sh.
+        if (shell.len > 0 and std.c.access(s, std.c.X_OK) == 0) return shell;
     };
     return "/bin/sh";
 }
@@ -1045,8 +1046,9 @@ pub const Runtime = struct {
                 }
             },
             .shell => {
-                const value = std.mem.trim(u8, argument orelse return false, " \t\r\n");
-                if (value.len == 0 or !state.shell.requested.set(value)) return false;
+                // Bare, the default again ($SHELL, else /bin/sh).
+                const value = std.mem.trim(u8, argument orelse "", " \t\r\n");
+                if (!state.shell.requested.set(value)) return false;
                 state.shell.pending = true;
             },
             .tagline_size => {