test(f3): fix test flakes

1. Reduce GPBFT delta to blockdelay/5 to match the expected mainnet
config and avoid timing out tests.
2. Make waiting for rebootstrap work in the presence of null tipsets.

itests/f3_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/filecoin-project/go-f3/manifest"
 	"github.com/filecoin-project/go-state-types/abi"
 
+	"github.com/filecoin-project/lotus/chain/types"
 	"github.com/filecoin-project/lotus/itests/kit"
 	"github.com/filecoin-project/lotus/node"
 	"github.com/filecoin-project/lotus/node/modules"
@@ -107,10 +108,17 @@ func (e *testEnv) waitTillF3Rebootstrap(timeout time.Duration) {
 		if err != nil || cert == nil {
 			return false
 		}
-		e.t.Log("here")
 		m, err := n.F3GetManifest(e.testCtx)
 		require.NoError(e.t, err)
-		e.t.Log("got manifest", cert.ECChain.Base().Epoch, m.BootstrapEpoch-m.EC.Finality)
+
+		// Find the first non-null block at or before the target height, that's the bootstrap block.
+		targetEpoch := m.BootstrapEpoch - m.EC.Finality
+		ts, err := n.ChainGetTipSetByHeight(e.testCtx, abi.ChainEpoch(targetEpoch), types.EmptyTSK)
+		if err != nil {
+			return false
+		}
+
+		e.t.Log("got manifest", cert.ECChain.Base().Epoch, int64(ts.Height()))
 		return cert.ECChain.Base().Epoch == m.BootstrapEpoch-m.EC.Finality
 	}, timeout)
 }

itests/kit/node_opts.go

@@ -220,6 +220,7 @@ func F3Enabled(bootstrapEpoch abi.ChainEpoch, blockDelay time.Duration, finality
 			c := lf3.NewConfig(manifestProvider, true, cid.Undef)(nn)
 			c.InitialManifest.Pause = false
 			c.InitialManifest.EC.Period = blockDelay
+			c.InitialManifest.Gpbft.Delta = blockDelay / 5
 			c.InitialManifest.EC.Finality = int64(finality)
 			c.InitialManifest.BootstrapEpoch = int64(bootstrapEpoch)
 			c.InitialManifest.EC.HeadLookback = 0