diff --git a/.github/workflows/taiko-client--test.yml b/.github/workflows/taiko-client--test.yml
index d827c943bbd..4c7d4338c1d 100644
--- a/.github/workflows/taiko-client--test.yml
+++ b/.github/workflows/taiko-client--test.yml
@@ -5,10 +5,16 @@ on:
     branches: [main]
     paths:
       - "packages/taiko-client/**"
+      - "packages/protocol/contracts/**"
+      - "packages/protocol/script/layer1/core/**"
   pull_request:
     types: [opened, synchronize, reopened, ready_for_review]
     paths:
       - "packages/taiko-client/**"
+      # The integration tests deploy these through `DeployProtocolOnL1`, so a change
+      # to them can break the client without touching a single client file.
+      - "packages/protocol/contracts/**"
+      - "packages/protocol/script/layer1/core/**"
       - "go.mod"
       - "go.sum"
       - "!**/*.md"
@@ -85,7 +91,6 @@ jobs:
     timeout-minutes: 30
     env:
       CGO_ENABLED: 1
-      PROTOCOL_FORK_DIR: protocol-taiko-mono
 
     strategy:
       fail-fast: false
@@ -100,13 +105,6 @@ jobs:
 
       - uses: actions/checkout@v7
 
-      - name: Checkout protocol for testing
-        uses: actions/checkout@v7
-        with:
-          repository: taikoxyz/taiko-mono
-          path: ${{ env.PROTOCOL_FORK_DIR }}
-          ref: main
-
       - name: Install Foundry
         uses: foundry-rs/foundry-toolchain@v1
 
@@ -159,14 +157,18 @@ jobs:
         with:
           cache-dependency-path: pnpm-lock.yaml
 
+      # Deploy the PR's own protocol contracts: a second checkout pinned to `main`
+      # would test different contracts on every re-run and never exercise a PR
+      # that changes protocol and client together.
       - name: Install pnpm dependencies for protocol
-        run: cd ./${{ env.PROTOCOL_FORK_DIR }}/packages/protocol && pnpm install
+        working-directory: packages/protocol
+        run: pnpm install
 
       - name: Run Tests on ${{ matrix.execution_node }} execution engine
         working-directory: packages/taiko-client
         env:
           L2_NODE: ${{ matrix.execution_node }}
-          PROTOCOL_DIR: ${{ github.workspace }}/${{ env.PROTOCOL_FORK_DIR }}/packages/protocol
+          PROTOCOL_DIR: ${{ github.workspace }}/packages/protocol
         run: make test
 
       - name: Codecov.io
diff --git a/.github/workflows/taiko-client-rs--test.yml b/.github/workflows/taiko-client-rs--test.yml
index 6db5a4b0f93..41afa484773 100644
--- a/.github/workflows/taiko-client-rs--test.yml
+++ b/.github/workflows/taiko-client-rs--test.yml
@@ -7,10 +7,16 @@ on:
     branches: [main]
     paths:
       - "packages/taiko-client-rs/**"
+      - "packages/protocol/contracts/**"
+      - "packages/protocol/script/layer1/core/**"
   pull_request:
     types: [opened, synchronize, reopened, ready_for_review]
     paths:
       - "packages/taiko-client-rs/**"
+      # The integration tests deploy these through `DeployProtocolOnL1`, so a change
+      # to them can break the client without touching a single client file.
+      - "packages/protocol/contracts/**"
+      - "packages/protocol/script/layer1/core/**"
       - "!**/*.md"
 
 concurrency:
diff --git a/packages/taiko-client/bindings/encoding/input_test.go b/packages/taiko-client/bindings/encoding/input_test.go
new file mode 100644
index 00000000000..aa933935954
--- /dev/null
+++ b/packages/taiko-client/bindings/encoding/input_test.go
@@ -0,0 +1,65 @@
+package encoding
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/stretchr/testify/require"
+)
+
+// basefeeSharingPctgRange covers every value the inbox accepts, both ends included:
+// `LibInboxSetup.validateConfig` requires `basefeeSharingPctg <= 100`, and taiko-geth
+// splits a transaction's basefee as `gasUsed * baseFee * pctg / 100` to the coinbase
+// with the remainder to the treasury. At 0 the coinbase is paid nothing, at 100 the
+// treasury is.
+var basefeeSharingPctgRange = []uint8{0, 1, 25, 75, 99, 100}
+
+// TestEncodeShastaExtraDataBasefeeSharingPctg round-trips the percentage byte through
+// the decoder both clients rely on, so a change to either end of the range shows up here
+// rather than as a block the drivers re-derive with different extraData.
+func TestEncodeShastaExtraDataBasefeeSharingPctg(t *testing.T) {
+	for _, pctg := range basefeeSharingPctgRange {
+		extraData, err := EncodeShastaExtraData(pctg, big.NewInt(1))
+		require.Nil(t, err)
+		require.Len(t, extraData, params.ShastaExtraDataLen)
+		require.Equal(t, pctg, core.DecodeShastaBasefeeSharingPctg(extraData))
+	}
+}
+
+// TestEncodeShastaExtraDataIndependentFields asserts the percentage and the proposal ID
+// never read each other's bytes, including when one of them is zero.
+func TestEncodeShastaExtraDataIndependentFields(t *testing.T) {
+	maxProposalID := new(big.Int).Sub(
+		new(big.Int).Lsh(big.NewInt(1), uint(params.ShastaExtraDataProposalIDLength*8)),
+		big.NewInt(1),
+	)
+
+	for _, pctg := range basefeeSharingPctgRange {
+		for _, proposalID := range []*big.Int{big.NewInt(0), big.NewInt(1), big.NewInt(1337), maxProposalID} {
+			extraData, err := EncodeShastaExtraData(pctg, proposalID)
+			require.Nil(t, err)
+
+			require.Equal(t, pctg, core.DecodeShastaBasefeeSharingPctg(extraData))
+
+			decodedID, err := core.DecodeShastaProposalID(extraData)
+			require.Nil(t, err)
+			require.Zero(t, proposalID.Cmp(decodedID))
+		}
+	}
+}
+
+// TestEncodeShastaExtraDataRejectsInvalidProposalID pins the three cases the encoder
+// refuses, so an out-of-range proposal ID never silently truncates into the percentage byte.
+func TestEncodeShastaExtraDataRejectsInvalidProposalID(t *testing.T) {
+	_, err := EncodeShastaExtraData(100, nil)
+	require.ErrorContains(t, err, "proposal ID is nil")
+
+	_, err = EncodeShastaExtraData(100, big.NewInt(-1))
+	require.ErrorContains(t, err, "proposal ID is negative")
+
+	tooLarge := new(big.Int).Lsh(big.NewInt(1), uint(params.ShastaExtraDataProposalIDLength*8))
+	_, err = EncodeShastaExtraData(100, tooLarge)
+	require.ErrorContains(t, err, "proposal ID too large")
+}