Update token reporting threshold (#970)

## Motivation


## Solution

.changeset/dry-turtles-sleep.md

@@ -0,0 +1,5 @@
+---
+"ccip": patch
+---
+
+#updated token price reporting observation threshold to improve safety duringphased rollout

core/services/ocr2/plugins/ccip/ccipcommit/ocr2.go

@@ -452,10 +452,10 @@ func extractObservationData(lggr logger.Logger, f int, observations []ccip.Commi
 
 	tokenPrices = make(map[cciptypes.Address][]*big.Int)
 	for token, tokenPriceObservations := range tokenPriceObservations {
-		// Token price is dropped if there are not enough valid observations. Depending on rollout status of job specs,
-		// it is possible for different nodes in the DON to observe different tokens. We can conclude a token should indeed
-		// be observed if there are at least f+1 valid observations.
-		if len(tokenPriceObservations) <= f {
+		// Token price is dropped if there are not enough valid observations. With a threshold of 2*(f-1) + 1, we achieve a balance between safety and liveness.
+		// During phased-rollout where some honest nodes may not have started observing the token yet, it requires 5 malicious node with 1 being the leader to successfully alter price.
+		// During regular operation, it requires 3 malicious nodes with 1 being the leader to temporarily delay price update for the token.
+		if len(tokenPriceObservations) < (2*(f-1) + 1) {
 			lggr.Warnf("Skipping token %s due to not enough valid observations: #obs=%d, f=%d", string(token), len(tokenPriceObservations), f)
 			continue
 		}

core/services/ocr2/plugins/ccip/ccipcommit/ocr2_test.go

@@ -730,9 +730,9 @@ func TestCommitReportingPlugin_extractObservationData(t *testing.T) {
 			expError: false,
 		},
 		{
-			name:               "tolerate 1 unsupported token with f=1",
+			name:               "tolerate 1 unsupported token with f=2",
 			commitObservations: []ccip.CommitObservation{ob1, ob2, obWithUnsupportedToken},
-			f:                  1,
+			f:                  2,
 			expIntervals:       []cciptypes.CommitStoreInterval{validInterval, validInterval, zeroInterval},
 			expGasPriceObs:     []*big.Int{ob1.SourceGasPriceUSD, ob2.SourceGasPriceUSD, obWithUnsupportedToken.SourceGasPriceUSD},
 			expTokenPriceObs: map[cciptypes.Address][]*big.Int{
@@ -753,22 +753,22 @@ func TestCommitReportingPlugin_extractObservationData(t *testing.T) {
 			expError: false,
 		},
 		{
-			name:               "tolerate mis-matched token observations with f=1",
-			commitObservations: []ccip.CommitObservation{ob1, obWithNilTokenPrice, obEmpty},
-			f:                  1,
+			name:               "tolerate mis-matched token observations with f=2",
+			commitObservations: []ccip.CommitObservation{ob1, obWithNilTokenPrice, obWithNilTokenPrice},
+			f:                  2,
 			expIntervals:       []cciptypes.CommitStoreInterval{validInterval, zeroInterval, zeroInterval},
-			expGasPriceObs:     []*big.Int{ob1.SourceGasPriceUSD, obWithNilTokenPrice.SourceGasPriceUSD},
+			expGasPriceObs:     []*big.Int{ob1.SourceGasPriceUSD, obWithNilTokenPrice.SourceGasPriceUSD, obWithNilTokenPrice.SourceGasPriceUSD},
 			expTokenPriceObs: map[cciptypes.Address][]*big.Int{
-				token1: {token1Price, token1Price},
+				token1: {token1Price, token1Price, token1Price},
 			},
 			expError: false,
 		},
 		{
-			name:               "tolerate all tokens filtered out with f=1",
-			commitObservations: []ccip.CommitObservation{ob1, obMissingTokenPrices},
-			f:                  1,
-			expIntervals:       []cciptypes.CommitStoreInterval{validInterval, zeroInterval},
-			expGasPriceObs:     []*big.Int{ob1.SourceGasPriceUSD, obMissingTokenPrices.SourceGasPriceUSD},
+			name:               "tolerate all tokens filtered out with f=2",
+			commitObservations: []ccip.CommitObservation{ob1, obMissingTokenPrices, obMissingTokenPrices},
+			f:                  2,
+			expIntervals:       []cciptypes.CommitStoreInterval{validInterval, zeroInterval, zeroInterval},
+			expGasPriceObs:     []*big.Int{ob1.SourceGasPriceUSD, obMissingTokenPrices.SourceGasPriceUSD, obMissingTokenPrices.SourceGasPriceUSD},
 			expTokenPriceObs:   map[cciptypes.Address][]*big.Int{},
 			expError:           false,
 		},