diff --git a/packages/scripts/src/lib/seed-perf-fixture.ts b/packages/scripts/src/lib/seed-perf-fixture.ts
index 3d882a4eb..a2c5e7966 100644
--- a/packages/scripts/src/lib/seed-perf-fixture.ts
+++ b/packages/scripts/src/lib/seed-perf-fixture.ts
@@ -528,7 +528,11 @@ function buildThreadEvents(args: ThreadEventBuildArgs): void {
               cwd: "",
               status: "completed",
               approvalStatus: null,
-              aggregatedOutput: makeOutput(rng, rng.int(10, 120)),
+              aggregatedOutput: makeOutput(
+                rng,
+                rng.int(10, 120) *
+                  (Number(process.env.BB_SEED_OUTPUT_LINE_SCALE ?? 1) || 1),
+              ),
             },
           },
         });
@@ -872,6 +876,11 @@ export function seedPerfFixture(
     options.threadCount,
     options.eventCount,
   );
+  // Issue #1131 repro: allow one giant thread (reporter: 44,246 events).
+  const giantThreadEvents = Number(process.env.BB_SEED_GIANT_THREAD_EVENTS ?? 0);
+  if (Number.isInteger(giantThreadEvents) && giantThreadEvents > 0) {
+    eventTargets[0] = giantThreadEvents;
+  }
 
   interface SeededThread {
     row: ThreadInsert;