diff --git a/crates/worker-runtime/src/worker_backend.rs b/crates/worker-runtime/src/worker_backend.rs
index 19233e5f..2b1123c8 100644
--- a/crates/worker-runtime/src/worker_backend.rs
+++ b/crates/worker-runtime/src/worker_backend.rs
@@ -2824,7 +2824,7 @@ mod tests {
 
     #[tokio::test]
     #[serial_test::serial(worker_allocation)]
-    async fn restore_pending_workspace_worker_without_system_prompt_fails_closed() {
+    async fn restore_legacy_workspace_worker_without_manifest_snapshot_requires_replacement() {
         let root = tempfile::tempdir().unwrap();
         let runtime_store_dir = root.path().join("runtime");
         let worker_ref = WorkerRef::new(crate::identity::WorkerId::from_legacy_u64(1));
@@ -2833,32 +2833,6 @@ mod tests {
             .join(worker_ref.worker_id.to_string());
         let worker_name = ProfileRuntimeWorkerFactory::runtime_worker_name_for_ref(&worker_ref);
         let session_id = session_store::new_session_id();
-        let manifest = manifest::WorkerManifest::from_toml(&format!(
-            r#"
-                [worker]
-                name = "{}"
-                pwd = "{}"
-
-                [model]
-                scheme = "anthropic"
-                model_id = "test-model"
-                auth = {{ kind = "none" }}
-
-                [engine]
-                max_tokens = 100
-
-                [feature.flow]
-                enabled = true
-
-                [[scope.allow]]
-                target = "{}"
-                permission = "write"
-            "#,
-            worker_name,
-            root.path().display(),
-            root.path().display(),
-        ))
-        .unwrap();
         WorkerAggregateStore::new(&worker_aggregate_dir, &worker_name)
             .unwrap()
             .set_active(
@@ -2866,7 +2840,7 @@ mod tests {
                 Some(session_store::WorkerActiveSegmentRef::pending_segment(
                     session_id,
                 )),
-                Some(serde_json::to_value(&manifest).unwrap()),
+                None,
             )
             .unwrap();
 
@@ -2899,10 +2873,10 @@ mod tests {
             })
             .await
         {
-            Ok(_) => panic!("pending Workspace Worker restore unexpectedly succeeded"),
+            Ok(_) => panic!("legacy Workspace Worker restore unexpectedly succeeded"),
             Err(error) => error,
         };
-        assert!(error.contains("requires operation-owned launch material"));
+        assert!(error.contains("replacement Worker is required"), "{error}");
     }
 
     #[tokio::test]
diff --git a/crates/worker/src/worker.rs b/crates/worker/src/worker.rs
index 01f9c0c9..2ebac04a 100644
--- a/crates/worker/src/worker.rs
+++ b/crates/worker/src/worker.rs
@@ -4819,6 +4819,13 @@ where
                 .ok_or_else(|| WorkerError::WorkerMetadataMissing {
                     worker_name: worker_name.to_string(),
                 })?;
+        if workspace_context.workspace_id().is_some()
+            && metadata.resolved_manifest_snapshot.is_none()
+        {
+            return Err(WorkerError::WorkerMetadataManifestSnapshotMissing {
+                worker_name: worker_name.to_string(),
+            });
+        }
         let active = metadata
             .active
             .ok_or_else(|| WorkerError::WorkerMetadataInactive {
@@ -4868,6 +4875,13 @@ where
                 .ok_or_else(|| WorkerError::WorkerMetadataMissing {
                     worker_name: worker_name.to_string(),
                 })?;
+        if workspace_context.workspace_id().is_some()
+            && metadata.resolved_manifest_snapshot.is_none()
+        {
+            return Err(WorkerError::WorkerMetadataManifestSnapshotMissing {
+                worker_name: worker_name.to_string(),
+            });
+        }
         let active = metadata
             .active
             .ok_or_else(|| WorkerError::WorkerMetadataInactive {
@@ -5769,7 +5783,9 @@ pub enum WorkerError {
         session_id: SessionId,
     },
 
-    #[error("worker metadata for {worker_name} does not include a resolved manifest snapshot")]
+    #[error(
+        "worker metadata for {worker_name} does not include a trusted resolved manifest snapshot; a replacement Worker is required"
+    )]
     WorkerMetadataManifestSnapshotMissing { worker_name: String },
 
     #[error(