Add WorkflowInterceptor extension point for named workflow interception

Introduce a pf4j ExtensionPoint that allows plugins to intercept
named workflow execution. This enables stage-level archiving and
resume capabilities without modifying workflow scripts.

- Add WorkflowInterceptor interface in nf-commons (ExtensionPoint)
- Extract WorkflowDef.runDefault() from run() (pure refactoring)
- Add interceptor lookup via Plugins.getExtension() in run()
- Entry workflows (name is null) are never intercepted

Signed-off-by: Zhibo Huang <huangzhibo@gmail.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: huangzhibo <zhibo90@126.com>

Author: huangzhibo

modules/nextflow/src/main/groovy/nextflow/script/WorkflowDef.groovy

@@ -24,6 +24,8 @@ import nextflow.exception.MissingProcessException
 import nextflow.exception.MissingValueException
 import nextflow.exception.ScriptRuntimeException
 import nextflow.extension.CH
+import nextflow.plugin.Plugins
+import nextflow.plugin.WorkflowInterceptor
 import nextflow.util.TestOnly
 /**
  * Models a script workflow component
@@ -181,6 +183,17 @@ class WorkflowDef extends BindableDef implements ChainableDef, IterableDef, Exec
     }
 
     Object run(Object[] args) {
+        final interceptor = name != null ? Plugins.getExtension(WorkflowInterceptor) : null
+        if( interceptor != null ) {
+            final result = interceptor.intercept(this, args, { runDefault(args) })
+            if( result instanceof ChannelOut )
+                this.output = result
+            return result
+        }
+        return runDefault(args)
+    }
+
+    private Object runDefault(Object[] args) {
         binding = new WorkflowBinding(owner)
         ExecutionStack.push(this)
         try {

modules/nf-commons/src/main/nextflow/plugin/WorkflowInterceptor.groovy

@@ -0,0 +1,32 @@
+package nextflow.plugin
+
+import org.pf4j.ExtensionPoint
+
+/**
+ * Extension point for intercepting named workflow execution.
+ *
+ * Plugins implement this interface to gain control before
+ * each named workflow runs. The interceptor uses the
+ * {@code proceed} callback to decide whether to execute
+ * the original workflow logic:
+ * - Call {@code proceed()} to execute normally, optionally
+ *   post-processing the result (e.g. archiving)
+ * - Return without calling {@code proceed()} to skip
+ *   execution (e.g. restore from archive)
+ *
+ * Entry workflows (name is null) are never intercepted.
+ *
+ * @author Zhibo Huang
+ */
+interface WorkflowInterceptor extends ExtensionPoint {
+
+    /**
+     * Intercept the execution of a named workflow.
+     *
+     * @param workflow the named workflow definition (WorkflowDef)
+     * @param args the arguments passed to the workflow
+     * @param proceed callback that executes the original workflow logic
+     * @return the workflow execution result (ChannelOut)
+     */
+    Object intercept(Object workflow, Object[] args, Closure proceed)
+}