Fix Azure Batch startTask concatenation issue (#6300)

Changes semicolon (;) concatenation to logical AND (&&) operator in
startTask command joining to ensure proper command chaining behavior.
This prevents Azure Batch from ignoring commands after the first
semicolon and provides better error handling when azcopy installation
or custom start tasks fail.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: adamrtalbot <[email protected]>

Author: adamrtalbot

plugins/nf-azure/src/main/nextflow/cloud/azure/batch/AzBatchService.groovy

@@ -835,7 +835,7 @@ class AzBatchService implements Closeable {
         }
 
         // otherwise return a StartTask object with the start task command and resource files
-        return new BatchStartTask(startCmd.join('; '))
+        return new BatchStartTask(startCmd.join(' && '))
             .setResourceFiles(resourceFiles)
             .setUserIdentity(userIdentity(opts.privileged, null, AutoUserScope.POOL))
     }

plugins/nf-azure/src/test/nextflow/cloud/azure/batch/AzBatchServiceTest.groovy

@@ -312,7 +312,7 @@ class AzBatchServiceTest extends Specification {
         when:
         def configuredStartTask = svc.createStartTask( new AzStartTaskOpts(script: 'echo hello-world') )
         then:
-        configuredStartTask.commandLine == 'bash -c "chmod +x azcopy && mkdir $AZ_BATCH_NODE_SHARED_DIR/bin/ && cp azcopy $AZ_BATCH_NODE_SHARED_DIR/bin/"; bash -c \'echo hello-world\''
+        configuredStartTask.commandLine == 'bash -c "chmod +x azcopy && mkdir $AZ_BATCH_NODE_SHARED_DIR/bin/ && cp azcopy $AZ_BATCH_NODE_SHARED_DIR/bin/" && bash -c \'echo hello-world\''
         and:
         configuredStartTask.resourceFiles.size()==1
         configuredStartTask.resourceFiles.first().filePath == 'azcopy'