diff --git a/itk/pom.xml b/itk/pom.xml
index b2d11e5d4..ca46a76ae 100644
--- a/itk/pom.xml
+++ b/itk/pom.xml
@@ -98,8 +98,49 @@
         </dependency>
     </dependencies>
 
+    <properties>
+        <!--
+          Single-source location of the canonical .proto files. The a2a-itk
+          repository is fetched at the ref pinned by A2A_ITK_REVISION (see
+          run_itk.sh) into ${project.basedir}/a2a-itk. Override via
+          -Da2a.itk.proto.dir=... when building outside run_itk.sh.
+        -->
+        <a2a.itk.proto.dir>${project.basedir}/a2a-itk/protos</a2a.itk.proto.dir>
+    </properties>
+
     <build>
         <plugins>
+            <plugin>
+                <!--
+                  Generates Java classes from the canonical instruction.proto
+                  fetched from a2a-itk. Mirrors the baseline configuration used
+                  by a2a-itk/agents/java/v10 so generated code (package `itk`,
+                  outer class `InstructionOuterClass`) stays byte-identical
+                  across the two paths during the strangler migration.
+                  Version is pinned inline to match spec-grpc/pom.xml (same
+                  plugin, same version) rather than reusing the parent's
+                  protobuf-maven-plugin.version property, which resolves to
+                  the org.xolstice plugin's version scheme (0.6.x) used by
+                  compat-0.3/spec-grpc.
+                -->
+                <groupId>io.github.ascopes</groupId>
+                <artifactId>protobuf-maven-plugin</artifactId>
+                <version>4.1.2</version>
+                <configuration>
+                    <protoc>${protobuf-java.version}</protoc>
+                    <sourceDirectories>
+                        <sourceDirectory>${a2a.itk.proto.dir}</sourceDirectory>
+                    </sourceDirectories>
+                </configuration>
+                <executions>
+                    <execution>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>generate</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
             <plugin>
                 <groupId>io.quarkus</groupId>
                 <artifactId>quarkus-maven-plugin</artifactId>
diff --git a/itk/run_itk.sh b/itk/run_itk.sh
index 0ab793490..7e4104450 100755
--- a/itk/run_itk.sh
+++ b/itk/run_itk.sh
@@ -31,7 +31,10 @@ cleanup() {
 # Register cleanup function to run on script exit
 trap cleanup EXIT
 
-# 1. Pull a2a-itk and checkout revision
+# 1. Pull a2a-itk and checkout revision.
+#    The clone doubles as the single source of truth for instruction.proto:
+#    protobuf-maven-plugin in itk/pom.xml reads it directly from
+#    ${project.basedir}/a2a-itk/protos (see the `a2a.itk.proto.dir` property).
 : "${A2A_ITK_REVISION:?A2A_ITK_REVISION environment variable must be set}"
 
 if [ ! -d "a2a-itk" ]; then
@@ -47,17 +50,14 @@ if git symbolic-ref -q HEAD > /dev/null; then
 fi
 cd ..
 
-# 2. Copy latest instruction.proto from a2a-itk
-cp a2a-itk/protos/instruction.proto src/main/proto/instruction.proto
-
-# 3. Build itk_service container image from root of a2a-itk
+# 2. Build itk_service container image from root of a2a-itk
 CONTAINER_BUILD_ARGS=""
 if [ "$CONTAINER_RT" = "podman" ]; then
   CONTAINER_BUILD_ARGS="--format docker"
 fi
 $CONTAINER_RT build $CONTAINER_BUILD_ARGS -t itk_service a2a-itk
 
-# 4. Start container service with a single mount: the a2a-java repo
+# 3. Start container service with a single mount: the a2a-java repo
 A2A_JAVA_ROOT=$(cd .. && pwd)
 
 # Stop existing container if any
@@ -80,7 +80,7 @@ $CONTAINER_RT run -d --name itk-service \
   -p 8000:8000 \
   itk_service
 
-# 5. Verify service is up and send post request
+# 4. Verify service is up and send post request
 MAX_RETRIES=30
 echo "Waiting for ITK service to start on 127.0.0.1:8000..."
 set +e
diff --git a/itk/src/main/proto/instruction.proto b/itk/src/main/proto/instruction.proto
deleted file mode 100644
index c607567aa..000000000
--- a/itk/src/main/proto/instruction.proto
+++ /dev/null
@@ -1,60 +0,0 @@
-syntax = "proto3";
-
-package itk;
-
-
-message Instruction {
-  // what should the "agent" do
-  oneof step {
-    CallAgent call_agent = 1;
-    ReturnResponse return_response = 2;
-    SeriesOfSteps steps = 3;
-  }
-}
-
-// Behavior messages
-message SendMessageBehavior {}
-message PushNotificationBehavior {
-  string url = 1;
-}
-message ResubscribeBehavior {}
-
-// gets the agent card from a remote agent, calls it and returns the response
-message CallAgent {
-  // which transport use to get agent card and later call
-  string transport = 1;
-  // where to get the agent card from
-  string agent_card_uri = 2;
-  // instruction for the called agent
-  Instruction instruction = 3;
-  // whether to use streaming
-  bool streaming = 4;
-
-  // behavior mode
-  oneof behavior {
-    SendMessageBehavior send_message = 5;
-    PushNotificationBehavior push_notification = 6;
-    ResubscribeBehavior resubscribe = 7;
-  }
-}
-
-// this option just returns a response
-message ReturnResponse {
-  // what to return to the calling agent
-  string response = 1;
-  // whether to hold the task in WORKING state instead of completing it
-  bool hold_task = 2;
-}
-
-// executes step series and returns response based on response_generator
-message SeriesOfSteps {
-  repeated Instruction instructions = 1;
-
-  enum ResponseGenerator {
-    // default
-    RESPONSE_GENERATOR_UNSPECIFIED = 0;
-    RESPONSE_GENERATOR_CONCAT = 1;
-  }
-
-  ResponseGenerator response_generator = 2;
-}
diff --git a/pom.xml b/pom.xml
index d0e6dbd38..2c1958176 100644
--- a/pom.xml
+++ b/pom.xml
@@ -599,8 +599,13 @@
         <module>transport/grpc</module>
         <module>transport/rest</module>
 
-        <!-- ITK (Integration Test Kit) agent -->
-        <module>itk</module>
+        <!--
+            ITK (Integration Test Kit) agent is intentionally NOT in the
+            default reactor because it consumes instruction.proto directly
+            from a sibling clone of a2a-itk that only exists at ITK test
+            time (fetched by itk/run_itk.sh). Enable via -Pitk when running
+            the ITK workflow.
+        -->
 
         <!-- A2A Protocol v0.3 backward compatibility layer -->
         <module>compat-0.3</module>
@@ -648,6 +653,19 @@
                 </plugins>
             </build>
         </profile>
+        <profile>
+            <!--
+                Adds the ITK (Integration Test Kit) agent module to the reactor.
+                Enabled by itk/run_itk.sh (via test_suite/current.py) which
+                fetches a2a-itk into itk/a2a-itk, providing the .proto sources
+                the module needs at generate-sources time. Off by default so
+                the standard reactor build works without an a2a-itk checkout.
+            -->
+            <id>itk</id>
+            <modules>
+                <module>itk</module>
+            </modules>
+        </profile>
         <profile>
             <!--
                 This profile gis required for old JDK that don't support reading type use annotations from bytecodes.