diff --git a/wfe-kubernetes/src/step.rs b/wfe-kubernetes/src/step.rs
index 02305ae..811980e 100644
--- a/wfe-kubernetes/src/step.rs
+++ b/wfe-kubernetes/src/step.rs
@@ -93,14 +93,35 @@ impl StepBody for KubernetesStep {
         // 2. Ensure namespace exists.
         ensure_namespace(&client, &ns, workflow_id).await?;
 
-        // 2b. If the definition declares a shared volume, ensure the PVC
+        // 2b. If the workflow declares a shared volume, ensure the PVC
         // exists in the namespace and compute the mount spec we'll inject
         // into the Job. The PVC is created once per namespace (one per
         // top-level workflow run) and reused by every step and
-        // sub-workflow. Backends with no definition in the step context
-        // (test fixtures) just skip the shared volume.
-        let shared_mount = if let Some(def) = context.definition {
-            if let Some(sv) = &def.shared_volume {
+        // sub-workflow.
+        //
+        // Check two sources: the step's definition (top-level workflow)
+        // and the inherited `_wfe_shared_volume` key in workflow.data
+        // (sub-workflows inherit it via parent-data propagation). The
+        // data path is the normal case for sub-workflows since only the
+        // root definition declares `shared_volume:`.
+        let shared_mount = {
+            // Try definition first (top-level workflow running its own steps).
+            let sv_from_def = context.definition.and_then(|d| d.shared_volume.as_ref());
+
+            // Fall back to inherited data (sub-workflow inherits parent data).
+            let sv_from_data: Option<wfe_core::models::SharedVolume> = if sv_from_def.is_none() {
+                context
+                    .workflow
+                    .data
+                    .get("_wfe_shared_volume")
+                    .and_then(|v| serde_json::from_value(v.clone()).ok())
+            } else {
+                None
+            };
+
+            let sv = sv_from_def.or(sv_from_data.as_ref());
+
+            if let Some(sv) = sv {
                 let size = sv
                     .size
                     .as_deref()
@@ -119,8 +140,6 @@ impl StepBody for KubernetesStep {
             } else {
                 None
             }
-        } else {
-            None
         };
 
         // 3. Merge env vars: workflow.data (uppercased) + config.env.
diff --git a/wfe-kubernetes/tests/integration.rs b/wfe-kubernetes/tests/integration.rs
index 0fbc276..21b6139 100644
--- a/wfe-kubernetes/tests/integration.rs
+++ b/wfe-kubernetes/tests/integration.rs
@@ -791,3 +791,113 @@ echo "##wfe[output file_count=$COUNT]"
     // Explicit cleanup (the guard still runs on panic paths).
     namespace::delete_namespace(&client, &ns).await.ok();
 }
+
+// ── Regression: sub-workflow inherits shared_volume via data ─────────
+//
+// The real CI topology is: ci (root, declares shared_volume) → checkout
+// sub-workflow (no shared_volume on its definition). The K8s executor
+// must pick up the shared_volume from the inherited `_wfe_shared_volume`
+// key in workflow.data, NOT from the sub-workflow's definition.
+//
+// This test was added after a production bug where the PVC was never
+// created because sub-workflow steps checked context.definition.shared_volume
+// which was None on the child definition.
+#[tokio::test]
+async fn sub_workflow_inherits_shared_volume_from_data() {
+    use tokio_util::sync::CancellationToken;
+    use wfe_core::models::{
+        ExecutionPointer, SharedVolume, WorkflowDefinition, WorkflowInstance, WorkflowStep,
+    };
+    use wfe_core::traits::step::{StepBody, StepExecutionContext};
+
+    let cluster = cluster_config();
+    let client = client::create_client(&cluster).await.unwrap();
+    let root_id = unique_id("subwf-pvc");
+
+    // The *child* definition does NOT declare shared_volume — this is
+    // the whole point. Only the root ci workflow declares it, and the
+    // config propagates via `_wfe_shared_volume` in workflow.data.
+    let child_definition = WorkflowDefinition::new("lint", 1);
+
+    // Simulate the data a sub-workflow receives from a root that has
+    // shared_volume. WorkflowHost::start_workflow_with_name injects
+    // `_wfe_shared_volume` into instance.data; SubWorkflowStep copies
+    // the parent's data into the child.
+    let child_data = serde_json::json!({
+        "repo_url": "https://example.com/repo.git",
+        "_wfe_shared_volume": {
+            "mount_path": "/workspace",
+            "size": "1Gi"
+        }
+    });
+
+    let child_instance = WorkflowInstance {
+        id: unique_id("child"),
+        name: "lint-regression-1".into(),
+        // Points at the root ci workflow — K8s executor derives the
+        // namespace from this, placing us in the root's namespace.
+        root_workflow_id: Some(root_id.clone()),
+        workflow_definition_id: "lint".into(),
+        version: 1,
+        description: None,
+        reference: None,
+        execution_pointers: vec![],
+        next_execution: None,
+        status: wfe_core::models::WorkflowStatus::Runnable,
+        data: child_data,
+        create_time: chrono::Utc::now(),
+        complete_time: None,
+    };
+
+    let ns = namespace::namespace_name(&cluster.namespace_prefix, &root_id);
+
+    // Step config — write a file to /workspace and verify it persists.
+    let mut step_cfg = step_config(
+        "alpine:3.18",
+        "echo pvc-ok > /workspace/pvc-test.txt && cat /workspace/pvc-test.txt",
+    );
+    step_cfg.namespace = Some(ns.clone());
+
+    let mut step = wfe_kubernetes::KubernetesStep::new(step_cfg, cluster.clone(), client.clone());
+
+    let mut ws = WorkflowStep::new(0, "pvc-check");
+    ws.name = Some("pvc-check".into());
+    let pointer = ExecutionPointer::new(0);
+
+    let ctx = StepExecutionContext {
+        item: None,
+        execution_pointer: &pointer,
+        persistence_data: None,
+        step: &ws,
+        workflow: &child_instance,
+        // definition has NO shared_volume — the executor must read
+        // _wfe_shared_volume from workflow.data instead.
+        definition: Some(&child_definition),
+        cancellation_token: CancellationToken::new(),
+        host_context: None,
+        log_sink: None,
+    };
+
+    let result = step.run(&ctx).await.unwrap_or_else(|e| {
+        panic!("pvc-check step failed (regression: sub-workflow shared_volume not inherited): {e}");
+    });
+    assert!(result.proceed);
+
+    // Verify the PVC was actually created in the namespace.
+    use k8s_openapi::api::core::v1::PersistentVolumeClaim;
+    let pvcs: kube::Api<PersistentVolumeClaim> = kube::Api::namespaced(client.clone(), &ns);
+    let pvc = pvcs.get("wfe-workspace").await;
+    assert!(
+        pvc.is_ok(),
+        "PVC 'wfe-workspace' should exist in namespace {ns}"
+    );
+
+    let output = result.output_data.unwrap();
+    let stdout = output["pvc-check.stdout"].as_str().unwrap_or("");
+    assert!(
+        stdout.contains("pvc-ok"),
+        "expected pvc-ok in stdout, got: {stdout}"
+    );
+
+    namespace::delete_namespace(&client, &ns).await.ok();
+}
diff --git a/wfe/src/host.rs b/wfe/src/host.rs
index dda335c..003f714 100644
--- a/wfe/src/host.rs
+++ b/wfe/src/host.rs
@@ -395,6 +395,20 @@ impl WorkflowHost {
             instance.execution_pointers.push(pointer);
         }
 
+        // If the definition declares a shared volume, stash it in the
+        // instance's data under a reserved key so sub-workflows inherit it
+        // automatically (via the parent-data-inheritance in SubWorkflowStep).
+        // The K8s executor reads it from workflow.data when
+        // context.definition.shared_volume is None.
+        if let Some(sv) = &definition.shared_volume {
+            if let Some(obj) = instance.data.as_object_mut() {
+                obj.insert(
+                    "_wfe_shared_volume".to_string(),
+                    serde_json::to_value(sv).unwrap_or_default(),
+                );
+            }
+        }
+
         // Assign a human-friendly name. Callers may override (e.g. webhook
         // handlers that want `ci-mainline-a1b2c3`); otherwise use the
         // sequenced default. Validation: reject empty overrides so the name