feat(cli): stderr class markers — diag module, campaign/verb-sugar retags

Iteration stderr-markers-1, tasks 1-2 of the stderr-class-markers plan
(spec signed via grounding-check PASS, decisions logged on #278).

The two stderr diagnostic classes become machine-separable (refs #278):
a new crate-internal diag module owns the grammar as note!/warning!
macros (`aura: note: <text>` benign continuing-run diagnostic,
`aura: warning: <text>` recorded fault the run survives); the four
undifferentiated sites are retagged — gate-emptied cell -> note,
failed cell / walkforward cell / mc cell -> warning — and the four
scaffold literals migrate onto the shared macro (output bytes
unchanged). The always-on record summary line gains the bare `aura: `
namespace it was missing; bare-prefix stays the vocabulary for error
lines accompanying a non-zero exit (C14 partition) and plain info
lines. Exit codes unchanged throughout.

Verification: RED->GREEN warning pin on the per-cell-fault e2e; new
gate-emptied e2e (impossible n_trades threshold) pins the note marker,
exit 0, and the summary-line prefix; scaffold e2es and the full
workspace suite green; clippy -D warnings clean on aura-cli. The C28
shell-module roster test gained the diag.rs entry.

Known residue for the next slices: aura-runner literals (stale-dylib
warning, three tap/no-nominee notes) and the #313 zero-trade notice
follow in tasks 3-5. The verb_sugar warning call sites remain e2e-
uncovered (a hostless walkforward fault fixture is structurally
unreachable — single-instrument validation refuses before the cell
loop); their grammar is pinned via the shared macro and the campaign
warning e2e.

refs #278

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 {

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};

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;

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)"
         );
     }
 }

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);
     }