Issue #166: snapshot --script exits non-zero when a scripted request fails

`fn snapshot` wrote every reply but never looked at `ok`, so a script with a
bad `ui.set`, an unknown command or a failed `ui.screenshot` exited 0 while
the PNG showed the wrong view or was never written. The run now counts
replies with `"ok": false`, keeps going (every reply still reaches stdout and
the final `-o` screenshot is still written — continue-and-report, like
`run --keep-going`) and returns `N scripted request(s) failed` afterwards,
which `main` turns into exit 1. Usage text and docs/control-protocol.md
"Headless rendering" state the contract.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

apps/lightcraft-cli/src/main.rs

@@ -71,6 +71,8 @@ USAGE:
                           per line: {\"method\": \"ui.set\", \"params\": {\"view\": \"detail\"}}.
                           Replies go to stdout. `ui.screenshot` without a path writes -o (then
                           OUT-2.png, OUT-3.png…); `ui.settle {timeoutMs?}` waits for renders.
+                          A failed request (\"ok\": false) does not stop the script, but the exit
+                          status is non-zero when any request failed.
         -o, --output OUT  PNG path (a final screenshot is written here if the script took none)
         --size WxH        window size in points (default 1600x1000)
         --scale S         pixels per point (default 1)
@@ -755,6 +757,9 @@ fn snapshot(args: &[String]) -> Result<(), String> {
         Some(p.with_file_name(format!("{stem}-{shots}.{ext}")).to_string_lossy().to_string())
     };
     let mut wrote_output = false;
+    // Issue #166: a scripted request that fails still gets its reply printed and the run carries
+    // on (like `run --keep-going`), but the exit status reports it — CI judges by exit status.
+    let mut failed = 0usize;
     if let Some(script) = &script {
         let text = std::fs::read_to_string(script).map_err(|e| format!("{script}: {e}"))?;
         let mut out = std::io::stdout().lock();
@@ -787,6 +792,9 @@ fn snapshot(args: &[String]) -> Result<(), String> {
                 }
                 _ => h.request(&method, params, timeout),
             };
+            if reply["ok"] != true {
+                failed += 1;
+            }
             if let Some(o) = reply.as_object_mut() {
                 o.insert("id".into(), id);
                 // wall time of the request (incl. the frames it ran), and since the start
@@ -823,7 +831,7 @@ fn snapshot(args: &[String]) -> Result<(), String> {
         }
     }
     eprintln!("lightcraft-cli snapshot: done in {:.2} s ({} frames)", t0.elapsed().as_secs_f64(), h.frames());
-    Ok(())
+    if failed > 0 { Err(format!("{failed} scripted request(s) failed")) } else { Ok(()) }
 }
 
 fn commands(args: &[String]) -> Result<(), String> {