Wire thread count and error behavior settings into executor

The PipelineExecutor now stores thread_count and pause_on_error
fields. When pause_on_error is enabled, the executor sets the
pause flag on failures so the user can review errors. The GUI
reads these settings from AppConfig before starting processing.

pixstrip-core/src/executor.rs

@@ -33,6 +33,8 @@ pub struct BatchResult {
 pub struct PipelineExecutor {
     cancel_flag: Arc<AtomicBool>,
     pause_flag: Arc<AtomicBool>,
+    thread_count: usize,
+    pause_on_error: bool,
 }
 
 impl PipelineExecutor {
@@ -40,6 +42,8 @@ impl PipelineExecutor {
         Self {
             cancel_flag: Arc::new(AtomicBool::new(false)),
             pause_flag: Arc::new(AtomicBool::new(false)),
+            thread_count: num_cpus(),
+            pause_on_error: false,
         }
     }
 
@@ -47,6 +51,8 @@ impl PipelineExecutor {
         Self {
             cancel_flag,
             pause_flag: Arc::new(AtomicBool::new(false)),
+            thread_count: num_cpus(),
+            pause_on_error: false,
         }
     }
 
@@ -57,9 +63,19 @@ impl PipelineExecutor {
         Self {
             cancel_flag,
             pause_flag,
+            thread_count: num_cpus(),
+            pause_on_error: false,
         }
     }
 
+    pub fn set_thread_count(&mut self, count: usize) {
+        self.thread_count = if count == 0 { num_cpus() } else { count };
+    }
+
+    pub fn set_pause_on_error(&mut self, pause: bool) {
+        self.pause_on_error = pause;
+    }
+
     pub fn execute<F>(&self, job: &ProcessingJob, mut on_progress: F) -> Result<BatchResult>
     where
         F: FnMut(ProgressUpdate) + Send,
@@ -122,6 +138,9 @@ impl PipelineExecutor {
                 Err(e) => {
                     result.failed += 1;
                     result.errors.push((file_name, e.to_string()));
+                    if self.pause_on_error {
+                        self.pause_flag.store(true, Ordering::Relaxed);
+                    }
                 }
             }
         }
@@ -198,3 +217,9 @@ impl Default for PipelineExecutor {
         Self::new()
     }
 }
+
+fn num_cpus() -> usize {
+    std::thread::available_parallelism()
+        .map(|n| n.get())
+        .unwrap_or(1)
+}