fix(desktop): reject conflicting headless modes

crates/op-host-desktop/src/main.rs

@@ -98,6 +98,7 @@ mod window_resize;
 mod window_state;
 
 use op_host_native::{NativeBackend, SharedSkiaContext, SharedSkiaError, WidgetHostNative};
+use std::ffi::OsStr;
 use std::path::PathBuf;
 use std::time::Instant;
 use winit::event_loop::{ControlFlow, EventLoop, EventLoopProxy};
@@ -538,6 +539,31 @@ fn init_tracing() {
         .try_init();
 }
 
+fn conflicting_headless_modes<I, S>(args: I) -> Option<Vec<&'static str>>
+where
+    I: IntoIterator<Item = S>,
+    S: AsRef<OsStr>,
+{
+    const MODE_FLAGS: [&str; 6] = [
+        "--mcp",
+        "--mcp-http",
+        "--serve-web",
+        "--tcc-selftest",
+        "--render-shots",
+        "--enrich-images",
+    ];
+    let mut requested = Vec::new();
+    for arg in args {
+        let arg = arg.as_ref();
+        for mode in MODE_FLAGS {
+            if arg == OsStr::new(mode) && !requested.contains(&mode) {
+                requested.push(mode);
+            }
+        }
+    }
+    (requested.len() > 1).then_some(requested)
+}
+
 fn main() {
     // FIRST, before any thread exists: graft the login-shell PATH and proxy
     // exports onto this process. A Dock/Finder launch inherits launchd's
@@ -566,6 +592,13 @@ fn main() {
         Err(err) => eprintln!("[fonts] skipping imported-font rescan: {err}"),
     }
     init_tracing();
+    if let Some(modes) = conflicting_headless_modes(std::env::args_os().skip(1)) {
+        eprintln!(
+            "openpencil-desktop: headless modes are mutually exclusive: {}",
+            modes.join(", ")
+        );
+        std::process::exit(2);
+    }
     // `--mcp` / `--mcp-http` swap the GUI for an MCP server mode;
     // when one of those ran, exit instead of opening a window.
     if mcp_serve::run_cli_if_requested() {

crates/op-host-desktop/src/main_tests.rs

@@ -4,6 +4,38 @@
 use super::*;
 use winit::keyboard::{Key, NamedKey};
 
+#[test]
+fn distinct_headless_modes_are_rejected_before_dispatch() {
+    assert_eq!(
+        conflicting_headless_modes([
+            "--render-shots",
+            "input.op",
+            "shots",
+            "--enrich-images",
+            "input.op",
+            "output.op",
+        ]),
+        Some(vec!["--render-shots", "--enrich-images"])
+    );
+    assert_eq!(
+        conflicting_headless_modes(["--mcp-http", "3100", "input.op", "--tcc-selftest"]),
+        Some(vec!["--mcp-http", "--tcc-selftest"])
+    );
+}
+
+#[test]
+fn one_headless_mode_or_repeated_same_flag_is_not_a_conflict() {
+    assert_eq!(
+        conflicting_headless_modes(["--render-shots", "input.op", "shots"]),
+        None
+    );
+    assert_eq!(
+        conflicting_headless_modes(["--enrich-images", "input.op", "--enrich-images"]),
+        None
+    );
+    assert_eq!(conflicting_headless_modes(["document.op"]), None);
+}
+
 #[test]
 fn cursor_only_redraw_without_visible_state_change_skips_present() {
     let mut app = DesktopApp::new(None);