docs: name the follow-up, and stop the scratch dir looking like a ticket id

improvise-udt2 is the ticket context/code/cli.md section 3 points at: a status
message carries no severity, so a refusal that does not abort cannot set a
non-zero exit. It names both disproved classifiers, so the next attempt does
not rediscover them.

And the per-test scratch directory was named `improvise-cli-<tag>`, which
matches the ticket-id shape the AGENTS.md audit greps for. An ID-shaped
non-ID is worse than a dead ID, because the diagnosis is identical and the
repair is not.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FC2jVn8Au7E9JPkw6bwXXH

tests/headless_cli.rs

@@ -12,7 +12,7 @@ struct Scratch(PathBuf);
 
 impl Scratch {
     fn new(tag: &str) -> Self {
-        let dir = std::env::temp_dir().join(format!("improvise-cli-{tag}-{}", std::process::id()));
+        let dir = std::env::temp_dir().join(format!("improv_cli_{tag}-{}", std::process::id()));
         let _ = std::fs::remove_dir_all(&dir);
         std::fs::create_dir_all(&dir).expect("a scratch directory");
         Self(dir)