fix(runner, campaign): contain synthetic member panics like the real path (GREEN)

The #272 containment recipe (SilencedPanic + catch_unwind +
panic_message) is exposed from aura-campaign as catch_member_panic and
applied at the bare-member seam in the synthetic family builders:
blueprint_sweep_family contains per-point, resolves the lowest
enumeration index's fault after the sweep joins (thread-order-
independent, C1), and exits deliberately with the aura: warning:
class marker + exit 3 (C14) instead of the raw panic/exit-101 escape;
blueprint_sweep_over captures instead of exiting (it runs inside the
per-window walkforward parallel closure — an on-the-spot exit would
race across windows) and hands the resolved fault up. Fault prose
reuses member_fault_prose; the real path's containment is untouched.

Deliberate residue, both tracked: blueprint_mc_family's member call
site keeps the bare run (empirical probe of the reachable surface
follows this commit; a reachable escape goes the same RED-first way),
and the new eprintln+exit(3) site in aura-runner joins the #297
process::exit inventory (noted there) rather than fighting M4's
future RunnerError propagation now.

Both RED e2es green; workspace suite green via the mini-verify;
clippy -D warnings clean on the touched crates. refs #278

crates/aura-campaign/src/exec.rs

@@ -830,6 +830,19 @@ fn panic_message(payload: Box<dyn std::any::Any + Send>) -> String {
         .unwrap_or_else(|| "member panicked (non-string payload)".to_string())
 }
 
+/// The `SilencedPanic` + `catch_unwind` + `panic_message` recipe above
+/// (this module's three call sites), exposed for reuse by a member-run caller
+/// OUTSIDE this crate that drives a bare member run without going through
+/// `execute` (#278: the synthetic blueprint sweep/walk-forward family
+/// builders in `aura-runner`, which share this exact bare-member seam but
+/// carry no #272 fault boundary of their own). Returns the panic payload's
+/// best-effort message on containment; `AssertUnwindSafe` is the same
+/// judgement documented on `panic_message` above.
+pub fn catch_member_panic<R>(f: impl FnOnce() -> R) -> Result<R, String> {
+    let _silence = SilencedPanic::enter();
+    std::panic::catch_unwind(std::panic::AssertUnwindSafe(f)).map_err(panic_message)
+}
+
 /// Assemble the (CellOutcome, CellRealization) pair for a cell that failed at a
 /// stage (#272): the realized stage prefix survives in `stages`, `families`/
 /// `selections` carry whatever already-persisted stages produced (empty for a

crates/aura-campaign/src/lib.rs

@@ -13,7 +13,8 @@
 
 mod exec;
 pub use exec::{
-    execute, member_fault_prose, CampaignOutcome, CellOutcome, StageFamily, StageSelectionOut,
+    catch_member_panic, execute, member_fault_prose, CampaignOutcome, CellOutcome, StageFamily,
+    StageSelectionOut,
 };
 
 use std::collections::BTreeMap;