diff --git a/README.md b/README.md
index 577c535..c219b79 100644
--- a/README.md
+++ b/README.md
@@ -48,3 +48,5 @@ nix run ./nix/test-cluster#cluster -- fresh-smoke
 ## Scope
 
 PhotonCloud is centered on reproducible infrastructure behavior rather than polished end-user product surfaces. Some services, such as `creditservice`, are intentionally minimal reference implementations that prove integration points rather than full products.
+
+Host-level NixOS rollout validation is also expected to stay reproducible: the `deployer-vm-smoke` VM test now proves that `nix-agent` can activate a prebuilt target system closure directly, without recompiling the stack inside the guest.
diff --git a/deployer/crates/deployer-ctl/src/chainfire.rs b/deployer/crates/deployer-ctl/src/chainfire.rs
index 7126737..fdc5878 100644
--- a/deployer/crates/deployer-ctl/src/chainfire.rs
+++ b/deployer/crates/deployer-ctl/src/chainfire.rs
@@ -236,7 +236,7 @@ fn desired_system_from_spec(node: &NodeSpec) -> Option<DesiredSystemSpec> {
     if desired.drain_before_apply.is_none() {
         desired.drain_before_apply = Some(false);
     }
-    if desired.nixos_configuration.is_some() {
+    if desired.nixos_configuration.is_some() || desired.target_system.is_some() {
         Some(desired)
     } else {
         None
@@ -882,7 +882,9 @@ pub async fn inspect_node(
                 if let Some(observed_system) = observed_system {
                     println!(
                         "observed_status={}",
-                        observed_system.status.unwrap_or_else(|| "unknown".to_string())
+                        observed_system
+                            .status
+                            .unwrap_or_else(|| "unknown".to_string())
                     );
                 }
             }
@@ -1090,7 +1092,8 @@ pub async fn set_host_deployment_paused(
         let deployment_name = deployment_name.to_string();
         async move {
             let mut client = Client::connect(endpoint).await?;
-            let spec_key = key_host_deployment_spec(&cluster_namespace, &cluster_id, &deployment_name);
+            let spec_key =
+                key_host_deployment_spec(&cluster_namespace, &cluster_id, &deployment_name);
             if client.get(&spec_key).await?.is_none() {
                 return Err(anyhow::anyhow!(
                     "host deployment {} not found",
@@ -1116,7 +1119,9 @@ pub async fn set_host_deployment_paused(
                 "resumed by operator".to_string()
             });
             status.updated_at = Some(Utc::now());
-            client.put(&status_key, &serde_json::to_vec(&status)?).await?;
+            client
+                .put(&status_key, &serde_json::to_vec(&status)?)
+                .await?;
             println!("{}", serde_json::to_string_pretty(&status)?);
             Ok(())
         }
@@ -1138,7 +1143,8 @@ pub async fn abort_host_deployment(
         let deployment_name = deployment_name.to_string();
         async move {
             let mut client = Client::connect(endpoint).await?;
-            let spec_key = key_host_deployment_spec(&cluster_namespace, &cluster_id, &deployment_name);
+            let spec_key =
+                key_host_deployment_spec(&cluster_namespace, &cluster_id, &deployment_name);
             if client.get(&spec_key).await?.is_none() {
                 return Err(anyhow::anyhow!(
                     "host deployment {} not found",
@@ -1512,6 +1518,7 @@ mod tests {
             node_id: String::new(),
             deployment_id: None,
             nixos_configuration: Some("node01-next".to_string()),
+            target_system: Some("/nix/store/node01-next".to_string()),
             flake_ref: Some("github:centra/cloud".to_string()),
             switch_action: Some("boot".to_string()),
             health_check_command: vec!["true".to_string()],
@@ -1523,6 +1530,10 @@ mod tests {
         let desired = desired_system_from_spec(&resolved[0]).expect("desired system should exist");
         assert_eq!(desired.node_id, "node01");
         assert_eq!(desired.nixos_configuration.as_deref(), Some("node01-next"));
+        assert_eq!(
+            desired.target_system.as_deref(),
+            Some("/nix/store/node01-next")
+        );
         assert_eq!(desired.flake_ref.as_deref(), Some("github:centra/cloud"));
         assert_eq!(desired.switch_action.as_deref(), Some("boot"));
         assert_eq!(desired.health_check_command, vec!["true".to_string()]);
diff --git a/deployer/crates/deployer-types/src/lib.rs b/deployer/crates/deployer-types/src/lib.rs
index 2704f60..ee4ca4c 100644
--- a/deployer/crates/deployer-types/src/lib.rs
+++ b/deployer/crates/deployer-types/src/lib.rs
@@ -605,6 +605,9 @@ pub struct DesiredSystemSpec {
     pub deployment_id: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub nixos_configuration: Option<String>,
+    /// Optional prebuilt NixOS system closure path to activate directly.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub target_system: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub flake_ref: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -756,6 +759,9 @@ pub struct HostDeploymentSpec {
     pub selector: HostDeploymentSelector,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub nixos_configuration: Option<String>,
+    /// Optional prebuilt NixOS system closure path handed directly to nix-agent.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub target_system: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub flake_ref: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -1238,6 +1244,7 @@ mod tests {
             node_id: "node01".to_string(),
             deployment_id: Some("worker-rollout".to_string()),
             nixos_configuration: Some("node01".to_string()),
+            target_system: Some("/nix/store/system-node01".to_string()),
             flake_ref: Some("/opt/plasmacloud-src".to_string()),
             switch_action: Some("switch".to_string()),
             health_check_command: vec!["systemctl".to_string(), "is-system-running".to_string()],
@@ -1250,6 +1257,10 @@ mod tests {
         assert_eq!(decoded.node_id, "node01");
         assert_eq!(decoded.deployment_id.as_deref(), Some("worker-rollout"));
         assert_eq!(decoded.nixos_configuration.as_deref(), Some("node01"));
+        assert_eq!(
+            decoded.target_system.as_deref(),
+            Some("/nix/store/system-node01")
+        );
         assert_eq!(decoded.health_check_command.len(), 2);
         assert_eq!(decoded.rollback_on_failure, Some(true));
         assert_eq!(decoded.drain_before_apply, Some(true));
@@ -1267,6 +1278,7 @@ mod tests {
                 match_labels: HashMap::from([("tier".to_string(), "general".to_string())]),
             },
             nixos_configuration: Some("worker-golden".to_string()),
+            target_system: Some("/nix/store/worker-golden".to_string()),
             flake_ref: Some("/opt/plasmacloud-src".to_string()),
             batch_size: Some(1),
             max_unavailable: Some(1),
@@ -1283,9 +1295,17 @@ mod tests {
         assert_eq!(decoded.name, "worker-rollout");
         assert_eq!(decoded.batch_size, Some(1));
         assert_eq!(decoded.max_unavailable, Some(1));
+        assert_eq!(
+            decoded.target_system.as_deref(),
+            Some("/nix/store/worker-golden")
+        );
         assert_eq!(decoded.selector.roles, vec!["worker".to_string()]);
         assert_eq!(
-            decoded.selector.match_labels.get("tier").map(String::as_str),
+            decoded
+                .selector
+                .match_labels
+                .get("tier")
+                .map(String::as_str),
             Some("general")
         );
         assert_eq!(decoded.drain_before_apply, Some(true));
@@ -1318,10 +1338,16 @@ mod tests {
 
         let json = serde_json::to_string(&node).unwrap();
         let decoded: ClusterNodeRecord = serde_json::from_str(&json).unwrap();
-        assert_eq!(decoded.commission_state, Some(CommissionState::Commissioned));
+        assert_eq!(
+            decoded.commission_state,
+            Some(CommissionState::Commissioned)
+        );
         assert_eq!(decoded.install_state, Some(InstallState::Installed));
         assert_eq!(decoded.power_state, Some(PowerState::On));
-        assert_eq!(decoded.bmc_ref.as_deref(), Some("redfish://lab-rack-a/node01"));
+        assert_eq!(
+            decoded.bmc_ref.as_deref(),
+            Some("redfish://lab-rack-a/node01")
+        );
     }
 
     #[test]
diff --git a/deployer/crates/nix-agent/src/main.rs b/deployer/crates/nix-agent/src/main.rs
index e375eec..abca814 100644
--- a/deployer/crates/nix-agent/src/main.rs
+++ b/deployer/crates/nix-agent/src/main.rs
@@ -97,7 +97,8 @@ struct Agent {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct ResolvedDesiredSystem {
-    nixos_configuration: String,
+    nixos_configuration: Option<String>,
+    target_system: Option<String>,
     flake_ref: String,
     switch_action: String,
     health_check_command: Vec<String>,
@@ -298,8 +299,7 @@ impl Agent {
             Some("draining")
                 if !desired
                     .map(|spec| {
-                        spec.deployment_id.is_some()
-                            && spec.drain_before_apply.unwrap_or(false)
+                        spec.deployment_id.is_some() && spec.drain_before_apply.unwrap_or(false)
                     })
                     .unwrap_or(false) =>
             {
@@ -321,7 +321,8 @@ impl Agent {
             return Ok(());
         };
         info!(
-            nixos_configuration = %desired.nixos_configuration,
+            nixos_configuration = desired.nixos_configuration.as_deref().unwrap_or(""),
+            target_system = desired.target_system.as_deref().unwrap_or(""),
             flake_ref = %desired.flake_ref,
             switch_action = %desired.switch_action,
             rollback_on_failure = desired.rollback_on_failure,
@@ -329,7 +330,7 @@ impl Agent {
             "resolved desired system"
         );
 
-        observed.nixos_configuration = Some(desired.nixos_configuration.clone());
+        observed.nixos_configuration = desired.nixos_configuration.clone();
         observed.flake_root = Some(desired.flake_ref.clone());
         observed.switch_action = Some(desired.switch_action.clone());
 
@@ -341,17 +342,25 @@ impl Agent {
             previous_system = previous_system.as_deref().unwrap_or(""),
             "selected rollback baseline"
         );
-        let target_system = self
-            .build_target_system(&desired.flake_ref, &desired.nixos_configuration)
-            .await
-            .with_context(|| {
-                format!(
-                    "failed to build target system for {}",
-                    desired.nixos_configuration
-                )
-            })?;
+        let target_system = match desired.target_system.as_deref() {
+            Some(target_system) => {
+                info!(target_system, "using prebuilt target system");
+                target_system.to_string()
+            }
+            None => {
+                let configuration = desired
+                    .nixos_configuration
+                    .as_deref()
+                    .ok_or_else(|| anyhow!("desired system did not specify nixos_configuration"))?;
+                self.build_target_system(&desired.flake_ref, configuration)
+                    .await
+                    .with_context(|| {
+                        format!("failed to build target system for {}", configuration)
+                    })?
+            }
+        };
         observed.target_system = Some(target_system.clone());
-        info!(target_system = %target_system, "built target system");
+        info!(target_system = %target_system, "resolved target system");
 
         if observed.current_system.as_deref() == Some(target_system.as_str()) {
             info!("target system already active");
@@ -575,10 +584,16 @@ fn resolve_desired_system(
             node.install_plan
                 .as_ref()
                 .and_then(|plan| plan.nixos_configuration.clone())
-        })?;
+        });
+    let target_system = desired.and_then(|spec| spec.target_system.clone());
+
+    if nixos_configuration.is_none() && target_system.is_none() {
+        return None;
+    }
 
     Some(ResolvedDesiredSystem {
         nixos_configuration,
+        target_system,
         flake_ref: desired
             .and_then(|spec| spec.flake_ref.clone())
             .unwrap_or_else(|| local_flake_root.to_string()),
@@ -787,7 +802,8 @@ mod tests {
             true,
         )
         .expect("desired system should resolve");
-        assert_eq!(resolved.nixos_configuration, "node01");
+        assert_eq!(resolved.nixos_configuration.as_deref(), Some("node01"));
+        assert_eq!(resolved.target_system, None);
         assert_eq!(resolved.flake_ref, "/opt/plasmacloud-src");
         assert_eq!(resolved.switch_action, "switch");
         assert!(resolved.rollback_on_failure);
@@ -799,6 +815,7 @@ mod tests {
             node_id: "node01".to_string(),
             deployment_id: None,
             nixos_configuration: Some("node01-next".to_string()),
+            target_system: None,
             flake_ref: Some("github:centra/cloud".to_string()),
             switch_action: Some("boot".to_string()),
             health_check_command: vec!["true".to_string()],
@@ -815,19 +832,52 @@ mod tests {
             false,
         )
         .expect("desired system should resolve");
-        assert_eq!(resolved.nixos_configuration, "node01-next");
+        assert_eq!(resolved.nixos_configuration.as_deref(), Some("node01-next"));
         assert_eq!(resolved.flake_ref, "github:centra/cloud");
         assert_eq!(resolved.switch_action, "boot");
         assert_eq!(resolved.health_check_command, vec!["true".to_string()]);
         assert!(resolved.rollback_on_failure);
     }
 
+    #[test]
+    fn resolve_desired_system_accepts_prebuilt_target_system() {
+        let desired = DesiredSystemSpec {
+            node_id: "node01".to_string(),
+            deployment_id: None,
+            nixos_configuration: Some("node01-next".to_string()),
+            target_system: Some("/nix/store/node01-next".to_string()),
+            flake_ref: None,
+            switch_action: Some("switch".to_string()),
+            health_check_command: Vec::new(),
+            rollback_on_failure: Some(true),
+            drain_before_apply: Some(false),
+        };
+
+        let resolved = resolve_desired_system(
+            &test_node(),
+            Some(&desired),
+            "/opt/plasmacloud-src",
+            "switch",
+            &[],
+            true,
+        )
+        .expect("desired system should resolve");
+
+        assert_eq!(resolved.nixos_configuration.as_deref(), Some("node01-next"));
+        assert_eq!(
+            resolved.target_system.as_deref(),
+            Some("/nix/store/node01-next")
+        );
+        assert_eq!(resolved.flake_ref, "/opt/plasmacloud-src");
+    }
+
     #[test]
     fn resolve_desired_system_uses_local_health_check_defaults_when_spec_omits_them() {
         let desired = DesiredSystemSpec {
             node_id: "node01".to_string(),
             deployment_id: None,
             nixos_configuration: Some("node01-next".to_string()),
+            target_system: None,
             flake_ref: None,
             switch_action: None,
             health_check_command: Vec::new(),
@@ -873,7 +923,8 @@ mod tests {
     #[test]
     fn post_boot_health_check_is_requested_for_matching_staged_target() {
         let desired = ResolvedDesiredSystem {
-            nixos_configuration: "node01".to_string(),
+            nixos_configuration: Some("node01".to_string()),
+            target_system: None,
             flake_ref: "/opt/plasmacloud-src".to_string(),
             switch_action: "boot".to_string(),
             health_check_command: vec!["true".to_string()],
@@ -895,7 +946,8 @@ mod tests {
     #[test]
     fn post_boot_health_check_is_skipped_for_non_matching_state() {
         let desired = ResolvedDesiredSystem {
-            nixos_configuration: "node01".to_string(),
+            nixos_configuration: Some("node01".to_string()),
+            target_system: None,
             flake_ref: "/opt/plasmacloud-src".to_string(),
             switch_action: "boot".to_string(),
             health_check_command: vec!["true".to_string()],
diff --git a/deployer/crates/plasmacloud-reconciler/src/hosts.rs b/deployer/crates/plasmacloud-reconciler/src/hosts.rs
index 9afe4ec..a17803e 100644
--- a/deployer/crates/plasmacloud-reconciler/src/hosts.rs
+++ b/deployer/crates/plasmacloud-reconciler/src/hosts.rs
@@ -4,7 +4,8 @@ use chrono::Utc;
 use clap::Args;
 use deployer_types::{
     ClusterNodeRecord, CommissionState, DesiredSystemSpec, HostDeploymentSelector,
-    HostDeploymentSpec, HostDeploymentStatus, InstallState, ObservedSystemState, ServiceInstanceSpec,
+    HostDeploymentSpec, HostDeploymentStatus, InstallState, ObservedSystemState,
+    ServiceInstanceSpec,
 };
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::time::Duration;
@@ -286,7 +287,9 @@ impl HostDeploymentController {
             let key = String::from_utf8_lossy(&key);
             match serde_json::from_slice::<ServiceInstanceSpec>(&value) {
                 Ok(instance) => instances.push(instance),
-                Err(error) => warn!(error = %error, key = %key, "failed to decode service instance"),
+                Err(error) => {
+                    warn!(error = %error, key = %key, "failed to decode service instance")
+                }
             }
         }
 
@@ -336,7 +339,9 @@ impl HostDeploymentController {
                 Ok(status) => {
                     statuses.insert(status.name.clone(), status);
                 }
-                Err(error) => warn!(error = %error, key = %key, "failed to decode host deployment status"),
+                Err(error) => {
+                    warn!(error = %error, key = %key, "failed to decode host deployment status")
+                }
             }
         }
 
@@ -393,17 +398,28 @@ fn plan_host_deployment(
     for node in &selector_matches {
         let desired = desired_systems.get(&node.node_id);
         let observed = observed_systems.get(&node.node_id);
-        let is_completed =
-            is_node_completed(deployment, node, desired, observed, target_configuration.as_deref());
+        let is_completed = is_node_completed(
+            deployment,
+            node,
+            desired,
+            observed,
+            target_configuration.as_deref(),
+        );
         let is_failed = is_node_failed(deployment, desired, observed);
-        let is_in_progress = is_node_in_progress(deployment, desired, observed, is_completed, is_failed)
-            || (deployment.drain_before_apply == Some(true)
-                && node.state.as_deref() == Some("draining")
-                && instance_counts.get(&node.node_id).copied().unwrap_or_default() > 0);
+        let is_in_progress =
+            is_node_in_progress(deployment, desired, observed, is_completed, is_failed)
+                || (deployment.drain_before_apply == Some(true)
+                    && node.state.as_deref() == Some("draining")
+                    && instance_counts
+                        .get(&node.node_id)
+                        .copied()
+                        .unwrap_or_default()
+                        > 0);
 
         if is_completed {
             completed.push(node.node_id.clone());
-            if deployment.drain_before_apply == Some(true) && node.state.as_deref() == Some("draining")
+            if deployment.drain_before_apply == Some(true)
+                && node.state.as_deref() == Some("draining")
             {
                 let mut updated = (*node).clone();
                 updated.state = Some("active".to_string());
@@ -431,11 +447,12 @@ fn plan_host_deployment(
     let paused = operator_paused || spec_paused || !failed.is_empty();
     let remaining_unavailable_budget = max_unavailable.saturating_sub(unavailable);
     let remaining_batch_budget = batch_size.saturating_sub(in_progress.len());
-    let max_starts = if deployment.nixos_configuration.is_some() {
-        remaining_unavailable_budget.min(remaining_batch_budget)
-    } else {
-        0
-    };
+    let max_starts =
+        if deployment.nixos_configuration.is_some() || deployment.target_system.is_some() {
+            remaining_unavailable_budget.min(remaining_batch_budget)
+        } else {
+            0
+        };
     let mut planned = 0usize;
     let mut newly_started = Vec::new();
 
@@ -445,7 +462,10 @@ fn plan_host_deployment(
                 break;
             }
 
-            let remaining_instances = instance_counts.get(&node.node_id).copied().unwrap_or_default();
+            let remaining_instances = instance_counts
+                .get(&node.node_id)
+                .copied()
+                .unwrap_or_default();
             if deployment.drain_before_apply == Some(true) && remaining_instances > 0 {
                 let mut updated = node.clone();
                 updated.state = Some("draining".to_string());
@@ -460,8 +480,12 @@ fn plan_host_deployment(
                 node_id: node.node_id.clone(),
                 deployment_id: Some(deployment.name.clone()),
                 nixos_configuration: deployment.nixos_configuration.clone(),
+                target_system: deployment.target_system.clone(),
                 flake_ref: deployment.flake_ref.clone(),
-                switch_action: deployment.switch_action.clone().or_else(|| Some("switch".to_string())),
+                switch_action: deployment
+                    .switch_action
+                    .clone()
+                    .or_else(|| Some("switch".to_string())),
                 health_check_command: deployment.health_check_command.clone(),
                 rollback_on_failure: Some(deployment.rollback_on_failure.unwrap_or(true)),
                 drain_before_apply: Some(deployment.drain_before_apply.unwrap_or(false)),
@@ -469,7 +493,8 @@ fn plan_host_deployment(
             newly_started.push(node.node_id.clone());
             in_progress.push(node.node_id.clone());
             planned += 1;
-            if deployment.drain_before_apply == Some(true) && node.state.as_deref() != Some("draining")
+            if deployment.drain_before_apply == Some(true)
+                && node.state.as_deref() != Some("draining")
             {
                 let mut updated = node.clone();
                 updated.state = Some("draining".to_string());
@@ -481,26 +506,31 @@ fn plan_host_deployment(
 
     let mut status = existing_status.cloned().unwrap_or_default();
     status.name = deployment.name.clone();
-    status.selected_nodes = selector_matches.iter().map(|node| node.node_id.clone()).collect();
+    status.selected_nodes = selector_matches
+        .iter()
+        .map(|node| node.node_id.clone())
+        .collect();
     status.completed_nodes = dedup_sorted(completed);
     status.in_progress_nodes = dedup_sorted(in_progress);
     status.failed_nodes = dedup_sorted(failed);
     status.paused_by_operator = operator_paused;
     status.paused = paused;
-    status.phase = Some(if status.selected_nodes.is_empty() {
-        "idle"
-    } else if deployment.nixos_configuration.is_none() {
-        "invalid"
-    } else if status.paused {
-        "paused"
-    } else if status.completed_nodes.len() == status.selected_nodes.len() {
-        "completed"
-    } else if !newly_started.is_empty() || !status.in_progress_nodes.is_empty() {
-        "running"
-    } else {
-        "ready"
-    }
-    .to_string());
+    status.phase = Some(
+        if status.selected_nodes.is_empty() {
+            "idle"
+        } else if deployment.nixos_configuration.is_none() && deployment.target_system.is_none() {
+            "invalid"
+        } else if status.paused {
+            "paused"
+        } else if status.completed_nodes.len() == status.selected_nodes.len() {
+            "completed"
+        } else if !newly_started.is_empty() || !status.in_progress_nodes.is_empty() {
+            "running"
+        } else {
+            "ready"
+        }
+        .to_string(),
+    );
     status.message = Some(format!(
         "selected={} completed={} in_progress={} failed={} newly_started={}",
         status.selected_nodes.len(),
@@ -585,9 +615,7 @@ fn node_is_rollout_candidate(node: &ClusterNodeRecord, heartbeat_timeout_secs: u
     }
     if matches!(
         node.install_state,
-        Some(
-            InstallState::Installing | InstallState::Failed | InstallState::ReinstallRequested
-        )
+        Some(InstallState::Installing | InstallState::Failed | InstallState::ReinstallRequested)
     ) {
         return false;
     }
@@ -612,9 +640,17 @@ fn is_node_completed(
 ) -> bool {
     observed
         .filter(|observed| observed.status.as_deref() == Some("active"))
-        .and_then(|observed| observed.nixos_configuration.as_deref())
-        .zip(target_configuration)
-        .map(|(observed_configuration, target)| observed_configuration == target)
+        .map(|observed| {
+            target_configuration
+                .map(|target| observed.nixos_configuration.as_deref() == Some(target))
+                .or_else(|| {
+                    deployment
+                        .target_system
+                        .as_deref()
+                        .map(|target| observed.target_system.as_deref() == Some(target))
+                })
+                .unwrap_or(false)
+        })
         .unwrap_or(false)
         && desired
             .and_then(|desired| desired.deployment_id.as_deref())
@@ -653,7 +689,12 @@ fn is_node_in_progress(
         .unwrap_or(false)
         || observed
             .and_then(|observed| observed.status.as_deref())
-            .map(|status| matches!(status, "planning" | "pending" | "reconciling" | "verifying" | "staged"))
+            .map(|status| {
+                matches!(
+                    status,
+                    "planning" | "pending" | "reconciling" | "verifying" | "staged"
+                )
+            })
             .unwrap_or(false)
 }
 
@@ -706,6 +747,7 @@ mod tests {
                 match_labels: HashMap::from([("tier".to_string(), "general".to_string())]),
             },
             nixos_configuration: Some("worker-golden".to_string()),
+            target_system: Some("/nix/store/worker-golden".to_string()),
             flake_ref: Some("/opt/plasmacloud-src".to_string()),
             batch_size: Some(1),
             max_unavailable: Some(1),
@@ -733,6 +775,10 @@ mod tests {
         );
 
         assert_eq!(plan.desired_upserts.len(), 1);
+        assert_eq!(
+            plan.desired_upserts[0].target_system.as_deref(),
+            Some("/nix/store/worker-golden")
+        );
         assert_eq!(plan.status.in_progress_nodes, vec!["node01".to_string()]);
         assert_eq!(plan.status.phase.as_deref(), Some("running"));
     }
@@ -747,6 +793,7 @@ mod tests {
                 node_id: "node01".to_string(),
                 deployment_id: Some("worker-rollout".to_string()),
                 nixos_configuration: Some("worker-golden".to_string()),
+                target_system: Some("/nix/store/worker-golden".to_string()),
                 flake_ref: None,
                 switch_action: Some("switch".to_string()),
                 health_check_command: Vec::new(),
@@ -764,15 +811,7 @@ mod tests {
             },
         )]);
 
-        let plan = plan_host_deployment(
-            &deployment,
-            None,
-            &nodes,
-            &desired,
-            &observed,
-            &[],
-            300,
-        );
+        let plan = plan_host_deployment(&deployment, None, &nodes, &desired, &observed, &[], 300);
 
         assert!(plan.desired_upserts.is_empty());
         assert!(plan.status.paused);
diff --git a/docs/testing.md b/docs/testing.md
index c8ec165..4d820ea 100644
--- a/docs/testing.md
+++ b/docs/testing.md
@@ -21,6 +21,7 @@ This flow:
 nix run ./nix/test-cluster#cluster -- fresh-smoke
 nix run ./nix/test-cluster#cluster -- fresh-matrix
 nix run ./nix/test-cluster#cluster -- fresh-bench-storage
+nix build .#checks.x86_64-linux.deployer-vm-smoke
 ```
 
 Use these three commands as the release-facing local proof set:
@@ -28,6 +29,7 @@ Use these three commands as the release-facing local proof set:
 - `fresh-smoke`: whole-cluster readiness, core behavior, and fault injection
 - `fresh-matrix`: composed service scenarios such as `prismnet + flashdns + fiberlb` and PrismNet-backed VM hosting bundles with `plasmavmc + coronafs + lightningstor`
 - `fresh-bench-storage`: CoronaFS local-vs-shared-volume throughput, cross-worker volume visibility, and LightningStor large/small-object throughput capture
+- `deployer-vm-smoke`: prebuilt NixOS system closure handoff into `nix-agent`, proving host rollout can activate a host-built target without guest-side compilation
 
 ## Operational Commands
 
diff --git a/nix/modules/cluster-config-lib.nix b/nix/modules/cluster-config-lib.nix
index 5702d0a..3a98fab 100644
--- a/nix/modules/cluster-config-lib.nix
+++ b/nix/modules/cluster-config-lib.nix
@@ -45,6 +45,12 @@ let
         description = "Name of the nixosConfigurations output to activate";
       };
 
+      targetSystem = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = "Optional prebuilt NixOS system closure path activated directly by nix-agent";
+      };
+
       flakeRef = mkOption {
         type = types.nullOr types.str;
         default = null;
@@ -128,6 +134,12 @@ let
           description = "Name of the nixosConfigurations output to roll out";
         };
 
+        targetSystem = mkOption {
+          type = types.nullOr types.str;
+          default = null;
+          description = "Optional prebuilt NixOS system closure path handed directly to nix-agent";
+        };
+
         flakeRef = mkOption {
           type = types.nullOr types.str;
           default = null;
@@ -963,6 +975,9 @@ let
         // optionalAttrs (desiredSystem != null && desiredSystem.nixosConfiguration != null) {
           nixos_configuration = desiredSystem.nixosConfiguration;
         }
+        // optionalAttrs (desiredSystem != null && desiredSystem.targetSystem != null) {
+          target_system = desiredSystem.targetSystem;
+        }
         // optionalAttrs (desiredSystem != null && desiredSystem.flakeRef != null) {
           flake_ref = desiredSystem.flakeRef;
         }
@@ -1000,6 +1015,9 @@ let
     // optionalAttrs (deployment.nixosConfiguration != null) {
       nixos_configuration = deployment.nixosConfiguration;
     }
+    // optionalAttrs (deployment.targetSystem != null) {
+      target_system = deployment.targetSystem;
+    }
     // optionalAttrs (deployment.flakeRef != null) {
       flake_ref = deployment.flakeRef;
     }
diff --git a/nix/tests/deployer-vm-smoke.nix b/nix/tests/deployer-vm-smoke.nix
index 0e19420..df7a6d1 100644
--- a/nix/tests/deployer-vm-smoke.nix
+++ b/nix/tests/deployer-vm-smoke.nix
@@ -103,6 +103,7 @@ in
     import time
 
     desired_system_overrides = json.loads("""${desiredSystemOverridesJson}""")
+    smoke_target_system = "${smokeTargetToplevel}"
 
     def write_remote_json(machine, path, payload):
         machine.succeed(
@@ -151,6 +152,7 @@ in
                     },
                     "desired_system": {
                         "nixos_configuration": "vm-smoke-target",
+                        "target_system": smoke_target_system,
                         **desired_system_overrides,
                     },
                     "state": "pending",
@@ -387,7 +389,7 @@ in
         assert observed["status"] == "${expectedStatus}", observed
         assert observed["nixos_configuration"] == "vm-smoke-target"
         assert observed["flake_root"] == "/var/lib/photon-src"
-        assert observed["target_system"].startswith("/nix/store/")
+        assert observed["target_system"] == smoke_target_system
         current_system = worker.succeed("readlink -f /run/current-system").strip()
         print("worker_current_system=", current_system)
         if ${if expectCurrentSystemMatchesTarget then "True" else "False"}: