diff --git a/src/application/services/storage_usage_service.rs b/src/application/services/storage_usage_service.rs
index c7337093..36ab045b 100644
--- a/src/application/services/storage_usage_service.rs
+++ b/src/application/services/storage_usage_service.rs
@@ -608,11 +608,11 @@ impl JobHandler for StorageUsageService {
     async fn run(&self, _args: &JobRunArgs) -> JobOutcome {
         let drives = match self.update_all_drives_storage_usage().await {
             Ok(n) => n,
-            Err(e) => return JobOutcome::Err(format!("drive reconciliation failed: {e}")),
+            Err(e) => return JobOutcome::err(format!("drive reconciliation failed: {e}")),
         };
         let users = match self.update_all_users_storage_usage().await {
             Ok(n) => n,
-            Err(e) => return JobOutcome::Err(format!("user reconciliation failed: {e}")),
+            Err(e) => return JobOutcome::err(format!("user reconciliation failed: {e}")),
         };
         JobOutcome::ok_with(
             drives + users,
diff --git a/src/infrastructure/scheduler/engine.rs b/src/infrastructure/scheduler/engine.rs
index 1f0f4f2b..35255d55 100644
--- a/src/infrastructure/scheduler/engine.rs
+++ b/src/infrastructure/scheduler/engine.rs
@@ -178,7 +178,7 @@ pub(super) async fn dispatch(name: &str, entry: Arc<JobEntry>, args: &JobRunArgs
                 // yield points may run to completion in the background.
                 // We still record timeout and release the permit.
                 (
-                    JobOutcome::Err(format!("wall-clock timeout of {:?} exceeded", dur)),
+                    JobOutcome::err(format!("wall-clock timeout of {:?} exceeded", dur)),
                     Some(ErrCause::Timeout),
                 )
             }
@@ -249,12 +249,12 @@ fn translate_join(
                 "unknown panic payload".to_string()
             };
             (
-                JobOutcome::Err(format!("handler panicked: {msg}")),
+                JobOutcome::err(format!("handler panicked: {msg}")),
                 Some(ErrCause::Panicked),
             )
         }
         Err(join_err) => (
-            JobOutcome::Err(format!("task cancelled: {join_err}")),
+            JobOutcome::err(format!("task cancelled: {join_err}")),
             Some(ErrCause::Handler),
         ),
     }
@@ -278,7 +278,7 @@ fn log_outcome(name: &str, outcome: &JobOutcome, cause: Option<ErrCause>, elapse
                 name,
             );
         }
-        JobOutcome::Err(msg) => {
+        JobOutcome::Err { message: msg } => {
             tracing::warn!(
                 target: "oxicloud::scheduler",
                 event = "job.run",
@@ -342,7 +342,7 @@ mod tests {
         let (outcome, cause) = translate_join(join.await);
         assert!(!outcome.is_ok());
         assert_eq!(cause, Some(ErrCause::Panicked));
-        if let JobOutcome::Err(msg) = outcome {
+        if let JobOutcome::Err { message: msg } = outcome {
             assert!(msg.contains("panicked"), "expected panic marker in: {msg}");
         }
     }
diff --git a/src/infrastructure/scheduler/types.rs b/src/infrastructure/scheduler/types.rs
index 88c2fecb..ed56dac6 100644
--- a/src/infrastructure/scheduler/types.rs
+++ b/src/infrastructure/scheduler/types.rs
@@ -51,7 +51,12 @@ pub enum JobOutcome {
         #[serde(default, skip_serializing_if = "serde_json::Value::is_null")]
         extra: serde_json::Value,
     },
-    Err(String),
+    /// `Err` is a struct variant (not tuple-newtype) so it composes
+    /// with `#[serde(tag = "outcome")]`. Serde's internal tagging
+    /// refuses to serialise a tuple variant wrapping a bare String
+    /// — the tag has nowhere to live. The struct form `{ message }`
+    /// lets serde emit `{"outcome":"err","message":"..."}` cleanly.
+    Err { message: String },
 }
 
 impl JobOutcome {
@@ -69,11 +74,19 @@ impl JobOutcome {
         JobOutcome::Ok { count, extra }
     }
 
+    /// Convenience constructor for `Err` — call-site ergonomics
+    /// match the retired tuple form.
+    pub fn err(message: impl Into<String>) -> Self {
+        JobOutcome::Err {
+            message: message.into(),
+        }
+    }
+
     /// Terse discriminant for logs / metrics: `"ok"` | `"err"`.
     pub fn kind(&self) -> &'static str {
         match self {
             JobOutcome::Ok { .. } => "ok",
-            JobOutcome::Err(_) => "err",
+            JobOutcome::Err { .. } => "err",
         }
     }
 
@@ -125,7 +138,7 @@ mod tests {
     #[test]
     fn joboutcome_kind_label() {
         assert_eq!(JobOutcome::ok(0).kind(), "ok");
-        assert_eq!(JobOutcome::Err("boom".into()).kind(), "err");
+        assert_eq!(JobOutcome::err("boom").kind(), "err");
     }
 
     #[test]
diff --git a/src/infrastructure/services/dedup_service.rs b/src/infrastructure/services/dedup_service.rs
index 17183957..77bbf417 100644
--- a/src/infrastructure/services/dedup_service.rs
+++ b/src/infrastructure/services/dedup_service.rs
@@ -3170,7 +3170,7 @@ impl crate::infrastructure::scheduler::JobHandler for DedupService {
                 items,
                 serde_json::json!({ "bytes_reclaimed": bytes, "forced": args.force }),
             ),
-            Err(e) => JobOutcome::Err(format!("dedup GC failed: {e}")),
+            Err(e) => JobOutcome::err(format!("dedup GC failed: {e}")),
         }
     }
 }
diff --git a/src/infrastructure/services/grant_cleanup_service.rs b/src/infrastructure/services/grant_cleanup_service.rs
index ce938d76..7dcde2aa 100644
--- a/src/infrastructure/services/grant_cleanup_service.rs
+++ b/src/infrastructure/services/grant_cleanup_service.rs
@@ -132,7 +132,7 @@ impl JobHandler for GrantCleanupService {
                     "forced": args.force,
                 }),
             ),
-            Err(e) => JobOutcome::Err(format!("grant cleanup failed: {e}")),
+            Err(e) => JobOutcome::err(format!("grant cleanup failed: {e}")),
         }
     }
 }
diff --git a/src/infrastructure/services/trash_cleanup_service.rs b/src/infrastructure/services/trash_cleanup_service.rs
index e008efa5..035ba992 100644
--- a/src/infrastructure/services/trash_cleanup_service.rs
+++ b/src/infrastructure/services/trash_cleanup_service.rs
@@ -183,7 +183,7 @@ impl JobHandler for TrashCleanupService {
                     }),
                 )
             }
-            Err(e) => JobOutcome::Err(format!("trash cleanup failed: {e}")),
+            Err(e) => JobOutcome::err(format!("trash cleanup failed: {e}")),
         }
     }
 }