ci(metis): harden transient agent failures

Jenkinsfile

@@ -2,6 +2,7 @@ pipeline {
   agent {
     kubernetes {
       defaultContainer 'builder'
+      retries 2
       yaml """
 apiVersion: v1
 kind: Pod
@@ -29,6 +30,7 @@ spec:
                 operator: NotIn
                 values:
                   - titan-13
+                  - titan-12
                   - titan-15
                   - titan-17
                   - titan-19
@@ -461,6 +463,7 @@ PY
   post {
     always {
       script {
+        try {
           if (fileExists(env.COVERAGE_JSON) && fileExists(env.JUNIT_XML)) {
             withEnv(["QUALITY_GATE_FINAL_STATUS=${currentBuild.currentResult ?: 'SUCCESS'}"]) {
               container('publisher') {
@@ -473,8 +476,16 @@ PY
           } else {
             echo 'quality metrics artifacts missing; skipping metrics publish'
           }
+        } catch (Throwable err) {
+          if (err.class.simpleName == 'MissingContextVariableException') {
+            echo 'workspace unavailable; skipping metrics publish'
+          } else {
+            throw err
+          }
+        }
       }
       script {
+        try {
           if (fileExists('build/junit.xml')) {
             try {
               junit allowEmptyResults: true, testResults: 'build/junit.xml'
@@ -482,8 +493,25 @@ PY
               echo "junit step unavailable: ${err.class.simpleName}"
             }
           }
+        } catch (Throwable err) {
+          if (err.class.simpleName == 'MissingContextVariableException') {
+            echo 'workspace unavailable; skipping junit publish'
+          } else {
+            throw err
           }
+        }
+      }
+      script {
+        try {
           archiveArtifacts artifacts: 'build/**', allowEmptyArchive: true, fingerprint: true
+        } catch (Throwable err) {
+          if (err.class.simpleName == 'MissingContextVariableException') {
+            echo 'workspace unavailable; skipping artifact archive'
+          } else {
+            throw err
+          }
+        }
+      }
     }
   }
 }