fix(config): tighten Fiber pending cap to 10 to bound submitter memory

ApplyFiberDefaults set MaxPendingHeadersAndData=50, but each pending
data item under Fiber is up to MaxBlobSize (~100 MiB raw). With
3-FSP fan-out and per-attempt retry buffers in flight, 50 items × 3
× retries crossed 64 GiB on c6in.8xlarge under sustained txsim load
and the kernel OOM-killed evnode 30 s into the run.

10 keeps the in-flight footprint bounded while still letting healthy
uploads pipeline against the actual Fibre RPC latency. Verified by
heap profiling: pending pause at ~ 10 × 100 MiB plus fan-out keeps
RSS below ~10 GiB, evnode runs indefinitely.

Author: walldiss

pkg/config/config.go

@@ -367,7 +367,12 @@ func (c *Config) ApplyFiberDefaults() {
 	}
 
 	c.DA.BlockTime = DurationWrapper{Duration: 1 * time.Second}
-	c.Node.MaxPendingHeadersAndData = 50
+	// Tighter pending cap (was 50). At 50, a Fibre upload stall lets the
+	// submitter accumulate 50 × ~32 MiB blob copies + their per-validator
+	// retry buffers; under load that exceeded c6in.8xlarge's 64 GiB and
+	// OOM-killed evnode at 63.8 GiB. 10 keeps the in-flight footprint
+	// bounded while still letting healthy uploads pipeline.
+	c.Node.MaxPendingHeadersAndData = 10
 }
 
 // GetNamespace returns the namespace for header submissions.