diff --git a/.github/scripts/codegen-check.sh b/.github/scripts/codegen-check.sh
new file mode 100755
index 0000000..0d15f3f
--- /dev/null
+++ b/.github/scripts/codegen-check.sh
@@ -0,0 +1,74 @@
+#!/usr/bin/env bash
+#
+# Renders tx3c's built-in `java-client` template against the canonical transfer
+# and complex fixtures, smoke-checks the generated surface, and compiles each
+# result against the SDK in this checkout.
+#
+# The template ships inside tx3c and pins the published `land.tx3:tx3-sdk`
+# version. Building against this checkout installed as a snapshot means an SDK
+# change that would break the client the current tx3c generates fails here,
+# before the SDK is released.
+#
+# Requires `tx3c` (0.25.0 or later, which ships the `java-client` template) on
+# PATH and a JDK 21; Maven comes from this checkout's wrapper.
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+work="$(mktemp -d)"
+trap 'rm -rf "$work"' EXIT
+m2="${CODEGEN_M2_REPO:-$work/m2}"
+snapshot="0.15.0-SNAPSHOT"
+mvnw="$repo_root/mvnw"
+
+"$mvnw" -B -ntp -f "$repo_root/pom.xml" -Drevision="$snapshot" \
+  -Dmaven.repo.local="$m2" -DskipTests install
+
+for fixture in transfer complex; do
+  gen="$work/$fixture"
+  tx3c codegen \
+    --tii "$repo_root/src/test/resources/fixtures/$fixture.tii" \
+    --template java-client \
+    --output "$gen"
+
+  test -f "$gen/pom.xml" || { echo "missing generated pom.xml ($fixture)"; exit 1; }
+  client="$(find "$gen/src/main/java/land/tx3/generated" -name '*Client.java' | head -n1)"
+  [[ -n "$client" ]] || { echo "missing generated *Client.java ($fixture)"; exit 1; }
+
+  # Public surface every generated client carries: protocol identity, the
+  # profile selector, and per-transaction TIR constants and Params records.
+  for pattern in \
+    'public static final String PROTOCOL_NAME' \
+    'public static final String PROTOCOL_VERSION' \
+    'public static final String TARGET_TII_VERSION = "v1beta0"' \
+    'public enum Profile' \
+    'Tx3ClientBuilder.fromParts('; do
+    grep -qF "$pattern" "$client" || { echo "generated $fixture client missing: $pattern"; exit 1; }
+  done
+  grep -qE 'public static final land\.tx3\.sdk\.TirEnvelope [A-Z0-9_]+_TIR' "$client" \
+    || { echo "generated $fixture client has no TIR constant"; exit 1; }
+  grep -qE 'public record [A-Za-z0-9]+Params\(' "$client" \
+    || { echo "generated $fixture client has no Params record"; exit 1; }
+
+  # Typed wrappers only: no generic party setter and no builder-only settings.
+  if grep -qE 'public [A-Za-z0-9]+Client with(Party|Profile|EnvValue|Header)\(' "$client"; then
+    echo "generated $fixture client exposes an untyped or builder-only setter"
+    exit 1
+  fi
+
+  echo "--- java-client/$fixture"
+  "$mvnw" -B -ntp -f "$gen/pom.xml" -Dmaven.repo.local="$m2" \
+    -Dtx3.sdk.version="$snapshot" verify
+done
+
+# The transfer fixture's typed surface, exactly.
+transfer_client="$(find "$work/transfer/src/main/java/land/tx3/generated" -name '*Client.java' | head -n1)"
+for pattern in \
+  'public record TransferParams(java.math.BigInteger quantity)' \
+  'PREPROD("preprod")' \
+  'TRANSFER_TIR' \
+  'Client withSender(land.tx3.sdk.Party party)' \
+  'Client withReceiver(land.tx3.sdk.Party party)' \
+  'Client withMiddleman(land.tx3.sdk.Party party)' \
+  'public land.tx3.sdk.TxBuilder transfer(TransferParams args)'; do
+  grep -qF "$pattern" "$transfer_client" || { echo "generated transfer client missing: $pattern"; exit 1; }
+done
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0fa53b1..309f76d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -112,29 +112,9 @@ jobs:
           distribution: temurin
           java-version: "21"
           cache: maven
-      - uses: dtolnay/rust-toolchain@1.91
-      - name: Install this checkout as the snapshot runtime
-        run: ./mvnw -B -ntp -Drevision=0.15.0-SNAPSHOT -Dmaven.repo.local="${RUNNER_TEMP}/codegen-m2" -DskipTests install
-      - name: Build pinned tx3c
-        uses: actions/checkout@v4
-        with:
-          repository: tx3-lang/tx3
-          ref: 456f68503a1306c865b17666a9ee1f1d801bd23b
-          path: .tx3c-source
-          persist-credentials: false
-      - run: cargo build -p tx3c --locked
-        working-directory: .tx3c-source
-      - name: Render and compile canonical fixtures
-        shell: bash
-        run: |
-          set -euo pipefail
-          for fixture in transfer complex; do
-            output="${RUNNER_TEMP}/generated-${fixture}"
-            .tx3c-source/target/debug/tx3c codegen \
-              --tii "src/test/resources/fixtures/${fixture}.tii" \
-              --template java-client \
-              --output "$output"
-            ./mvnw -B -ntp -f "$output/pom.xml" \
-              -Dmaven.repo.local="${RUNNER_TEMP}/codegen-m2" \
-              -Dtx3.sdk.version=0.15.0-SNAPSHOT verify
-          done
+      - name: Setup tx3 toolchain
+        uses: tx3-lang/actions/setup@v1
+      - name: Render, smoke-check, and compile the generated client
+        env:
+          CODEGEN_M2_REPO: ${{ runner.temp }}/codegen-m2
+        run: bash .github/scripts/codegen-check.sh