diff --git a/crates/aura-cli/src/campaign_run.rs b/crates/aura-cli/src/campaign_run.rs
index eb4040b..2a8aa99 100644
--- a/crates/aura-cli/src/campaign_run.rs
+++ b/crates/aura-cli/src/campaign_run.rs
@@ -315,8 +315,8 @@ fn present_campaign(
     for cell in &outcome.record.cells {
         for (stage_ix, st) in cell.stages.iter().enumerate() {
             if matches!(&st.survivor_ordinals, Some(v) if v.is_empty()) {
-                eprintln!(
-                    "aura: cell {}/{}/[{}, {}]: gate at stage {stage_ix} left no \
+                crate::diag::note!(
+                    "cell {}/{}/[{}, {}]: gate at stage {stage_ix} left no \
                      survivors; cell realization truncated",
                     cell.strategy, cell.instrument, cell.window_ms.0, cell.window_ms.1
                 );
@@ -333,8 +333,8 @@ fn present_campaign(
         if let Some(f) = &cell.fault {
             failed += 1;
             fail_labels.push(format!("{}: {}", cell.instrument, cell_fault_kind_label(f.kind)));
-            eprintln!(
-                "aura: cell ({}, {}, [{}, {}]) failed at stage {}: {} — recorded, campaign continues",
+            crate::diag::warning!(
+                "cell ({}, {}, [{}, {}]) failed at stage {}: {} — recorded, campaign continues",
                 cell.strategy, cell.instrument, cell.window_ms.0, cell.window_ms.1, f.stage, f.detail
             );
         }
@@ -388,7 +388,7 @@ fn present_campaign(
                 .expect("campaign run record serializes")
         );
         eprintln!(
-            "campaign run {} recorded: {} cells{}",
+            "aura: campaign run {} recorded: {} cells{}",
             outcome.record.run,
             outcome.record.cells.len(),
             if failed == 0 {
diff --git a/crates/aura-cli/src/diag.rs b/crates/aura-cli/src/diag.rs
new file mode 100644
index 0000000..3f9a36e
--- /dev/null
+++ b/crates/aura-cli/src/diag.rs
@@ -0,0 +1,20 @@
+//! Stable stderr class markers (C14): `aura: note: <text>` for benign
+//! diagnostics on a continuing run (exit code unaffected),
+//! `aura: warning: <text>` for recorded faults the run survives.
+//! Error lines that accompany a non-zero exit — and plain info lines
+//! such as the run-record summary — keep the bare `aura:` prefix; for
+//! errors, the exit-code partition is the machine contract.
+
+macro_rules! note {
+    ($($arg:tt)*) => {
+        eprintln!("aura: note: {}", format_args!($($arg)*))
+    };
+}
+
+macro_rules! warning {
+    ($($arg:tt)*) => {
+        eprintln!("aura: warning: {}", format_args!($($arg)*))
+    };
+}
+
+pub(crate) use {note, warning};
diff --git a/crates/aura-cli/src/main.rs b/crates/aura-cli/src/main.rs
index 1d243c8..57010f4 100644
--- a/crates/aura-cli/src/main.rs
+++ b/crates/aura-cli/src/main.rs
@@ -3,6 +3,7 @@
 //! (or the `--strategy r-sma` sugar) and print canonical JSON metrics/manifests;
 //! this binary authors no built-in harness.
 
+mod diag;
 mod render;
 mod graph_construct;
 mod campaign_run;
diff --git a/crates/aura-cli/src/scaffold.rs b/crates/aura-cli/src/scaffold.rs
index 7cedbda..8d705de 100644
--- a/crates/aura-cli/src/scaffold.rs
+++ b/crates/aura-cli/src/scaffold.rs
@@ -283,7 +283,7 @@ pub fn scaffold_project(spec: &ProjectScaffoldSpec) -> Result<(), String> {
         Ok(o) if o.status.success() => {
             commit_all(&spec.target_dir, "aura new scaffold");
         }
-        _ => eprintln!("aura: warning: git init failed (project created without a repo)"),
+        _ => crate::diag::warning!("git init failed (project created without a repo)"),
     }
     Ok(())
 }
@@ -324,7 +324,7 @@ pub fn scaffold_node_crate(spec: &ScaffoldSpec) -> Result<(), String> {
         Ok(o) if o.status.success() => {
             commit_all(&spec.target_dir, "aura nodes new scaffold");
         }
-        _ => eprintln!("aura: warning: git init failed (node crate created without a repo)"),
+        _ => crate::diag::warning!("git init failed (node crate created without a repo)"),
     }
     Ok(())
 }
@@ -357,7 +357,7 @@ fn commit_all(dir: &std::path::Path, message: &str) {
         .current_dir(dir)
         .output();
     if !matches!(add, Ok(o) if o.status.success()) {
-        eprintln!("aura: warning: git add failed (scaffold created without an initial commit)");
+        crate::diag::warning!("git add failed (scaffold created without an initial commit)");
         return;
     }
     let commit = std::process::Command::new("git")
@@ -374,8 +374,8 @@ fn commit_all(dir: &std::path::Path, message: &str) {
         .current_dir(dir)
         .output();
     if !matches!(commit, Ok(o) if o.status.success()) {
-        eprintln!(
-            "aura: warning: git commit failed (scaffold created without an initial commit)"
+        crate::diag::warning!(
+            "git commit failed (scaffold created without an initial commit)"
         );
     }
 }
diff --git a/crates/aura-cli/src/verb_sugar.rs b/crates/aura-cli/src/verb_sugar.rs
index dc2b964..a270f58 100644
--- a/crates/aura-cli/src/verb_sugar.rs
+++ b/crates/aura-cli/src/verb_sugar.rs
@@ -526,7 +526,7 @@ pub(crate) fn run_walkforward_sugar(
     )?;
 
     if let Some(f) = run.outcome.record.cells.iter().find_map(|c| c.fault.as_ref()) {
-        eprintln!("aura: walkforward cell failed at stage {}: {}", f.stage, f.detail);
+        crate::diag::warning!("walkforward cell failed at stage {}: {}", f.stage, f.detail);
         return Ok(1);
     }
 
@@ -690,7 +690,7 @@ pub(crate) fn run_mc_sugar(
     )?;
 
     if let Some(f) = run.outcome.record.cells.iter().find_map(|c| c.fault.as_ref()) {
-        eprintln!("aura: mc cell failed at stage {}: {}", f.stage, f.detail);
+        crate::diag::warning!("mc cell failed at stage {}: {}", f.stage, f.detail);
         return Ok(1);
     }
 
diff --git a/crates/aura-cli/tests/research_docs.rs b/crates/aura-cli/tests/research_docs.rs
index a251532..04c0b94 100644
--- a/crates/aura-cli/tests/research_docs.rs
+++ b/crates/aura-cli/tests/research_docs.rs
@@ -1452,6 +1452,19 @@ const SWEEP_ONLY_PROCESS_DOC: &str = r#"{
   "pipeline": [ { "block": "std::sweep", "metric": "sqn_normalized", "select": "argmax" } ]
 }"#;
 
+/// A gate no realized sweep member can ever satisfy (`n_trades ge 999999`) —
+/// deterministically empties `survivor_ordinals` regardless of the fixture's
+/// actual trade counts, driving the #278 zero-survivor NOTE marker.
+const GATE_EMPTIES_PROCESS_DOC: &str = r#"{
+  "format_version": 1,
+  "kind": "process",
+  "name": "gate-empties",
+  "pipeline": [
+    { "block": "std::sweep", "metric": "sqn_normalized", "select": "argmax" },
+    { "block": "std::gate", "all": [ { "metric": "n_trades", "cmp": "ge", "value": 999999.0 } ] }
+  ]
+}"#;
+
 /// The full annotated shape for the gated e2e: sweep -> gate -> walk_forward
 /// -> monte_carlo. The gate (`n_trades ge 0`) passes every member, so
 /// walk-forward always has survivors; the mc annotator bootstraps the pooled
@@ -1978,6 +1991,57 @@ fn campaign_run_synthetic_e2e_parallel_instruments_contains_a_real_per_cell_faul
     assert_eq!(cells[1]["instrument"].as_str(), Some("SYMB"), "doc order preserved: {line}");
     assert!(cells[0]["fault"].is_null(), "SYMA has data in January, its cell succeeds: {line}");
     assert!(!cells[1]["fault"].is_null(), "SYMB has no January data, its cell is faulted: {line}");
+    assert!(
+        out.contains("aura: warning: cell ("),
+        "the failed-cell line carries the warning class marker (#278): {out}"
+    );
+}
+
+/// #278 sibling of the warning-class pin above: a gate that empties a cell's
+/// survivors (never a fault, #198 decision 8) emits the NOTE class marker,
+/// not the bare `aura:` prefix nor `warning:`. `GATE_EMPTIES_PROCESS_DOC`'s
+/// impossible threshold guarantees zero survivors regardless of the
+/// fixture's actual sweep-member trade counts. Second property pinned on the
+/// same invocation: the run's terminal "recorded" summary line — previously
+/// printed with NO `aura:` prefix at all — now carries it too, so every
+/// stderr line this command emits (per-cell class markers AND the run-level
+/// summary) shares the one `aura:`-rooted vocabulary; a regression that
+/// reverted just this one un-tagged `eprintln!` back to a bare line would
+/// not be caught by the note-marker assertion above.
+#[test]
+fn campaign_run_synthetic_e2e_gate_emptied_cell_carries_the_note_marker() {
+    let (dir, _fixture) = fresh_project_with_data();
+    let runs_dir = dir.join("runs");
+    std::fs::remove_dir_all(&runs_dir).ok();
+    let _cleanup = ScratchGuard(vec![
+        ScratchPath::Dir(runs_dir.clone()),
+        ScratchPath::File(dir.join("gateempty.process.json")),
+        ScratchPath::File(dir.join("gateempty.campaign.json")),
+    ]);
+    let bp_id = seed_blueprint(&dir, "campaign-run-gateempty-seed");
+    let proc_id =
+        register_process_doc(&dir, "gateempty.process.json", GATE_EMPTIES_PROCESS_DOC);
+    let doc = campaign_doc_json_for(
+        "SYMA",
+        &bp_id,
+        &proc_id,
+        (1704844800000, 1705708800000),
+        "",
+        "",
+    );
+    write_doc(&dir, "gateempty.campaign.json", &doc);
+
+    let (out, code) =
+        run_code_in(&dir, &["campaign", "run", "gateempty.campaign.json"]);
+    assert_eq!(code, Some(0), "a zero-survivor cell is a valid result, not a fault: {out}");
+    assert!(
+        out.contains("aura: note: cell "),
+        "the gate-emptied cell line carries the note class marker (#278): {out}"
+    );
+    assert!(
+        out.contains("aura: campaign run "),
+        "the run-level recorded summary line also carries the aura: prefix (#278): {out}"
+    );
 }
 
 /// The v2 boundary, campaign side: a generalize-bearing process is an
diff --git a/crates/aura-vocabulary/tests/c28_layering.rs b/crates/aura-vocabulary/tests/c28_layering.rs
index 8c12005..7da26e5 100644
--- a/crates/aura-vocabulary/tests/c28_layering.rs
+++ b/crates/aura-vocabulary/tests/c28_layering.rs
@@ -179,6 +179,7 @@ fn the_shell_defines_no_domain_modules_and_no_lib_target() {
         modules,
         [
             "campaign_run.rs",
+            "diag.rs",
             "graph_construct.rs",
             "main.rs",
             "render.rs",