diff --git a/backend/src/routes/sessions.ts b/backend/src/routes/sessions.ts
index 7f1299a8..0602cf1f 100644
--- a/backend/src/routes/sessions.ts
+++ b/backend/src/routes/sessions.ts
@@ -142,7 +142,11 @@ export function sessionRoutes(
         info(id, "Starting model");
         if (d.mgr.get(id) !== rt) return;
         start();
-      } catch {
+      } catch (error) {
+        // The client only ever sees the generic BOOTSTRAP_FAILURE_MESSAGE; log the real
+        // cause server-side so failures (e.g. an unreachable DWH/vector host behind a
+        // dropped VPN) are diagnosable from the backend console instead of silent.
+        console.error(`[pi:${id}] bootstrap failed:`, error instanceof Error ? error.message : error);
         void withSessionLifecycle(id, async () => {
           // A bootstrap continuation can settle after Close/Delete or after a replacement was
           // installed. Claim only the runtime identity that actually failed; holding the same