diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e9e75964..18481e37 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -73,7 +73,7 @@ jobs:
             ${{ runner.os }}-sbt-
 
       - name: Run tests with coverage
-        run: sbt clean coverage sharedData/test coverageReport
+        run: sbt clean coverage proto/compile proto/test sharedData/test coverageReport
 
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4
diff --git a/modules/proto/README.md b/modules/proto/README.md
new file mode 100644
index 00000000..6c8e5abb
--- /dev/null
+++ b/modules/proto/README.md
@@ -0,0 +1,145 @@
+# OttoChain Proto Module
+
+This module provides Protocol Buffer definitions and ScalaPB-generated Scala types for OttoChain data structures.
+
+## Build-Time Generation Strategy
+
+### ScalaPB Configuration
+
+The module uses **build-time generation** via sbt-protoc and ScalaPB:
+
+```scala
+Compile / PB.targets := Seq(
+  scalapb.gen(flatPackage = true) -> (Compile / sourceManaged).value / "scalapb",
+  scalapb.validate.gen() -> (Compile / sourceManaged).value / "scalapb"
+)
+```
+
+**Generated files location:** `target/scala-2.13/src_managed/main/scalapb/` (gitignored)
+
+**Benefits:**
+- Consistent with Tessellation's build strategy
+- Generated types available at compile time
+- No runtime protoc dependencies
+- IDE integration works seamlessly
+
+### DataUpdate Mixin Integration
+
+All OttoChain message types extend `io.constellationnetwork.currency.dataApplication.DataUpdate` via ScalaPB options:
+
+```protobuf
+message CreateStateMachine {
+  option (scalapb.message).extends = "io.constellationnetwork.currency.dataApplication.DataUpdate";
+  // ...
+}
+```
+
+This enables:
+- Direct submission to Tessellation's DataL1
+- Type-safe metagraph integration
+- Seamless ML0 processing
+
+## Type System Architecture
+
+### Proto vs. Scala Model Boundary
+
+**Key architectural decision:** Proto types and Scala domain models serve different purposes and coexist:
+
+- **Proto types** (`ottochain.v1.*`): Wire format, serialization, network transport
+- **Scala models** (`xyz.kd5ujc.models.*`): Domain logic, business rules, type safety
+
+### ProtoAdapters Migration Strategy
+
+The `ProtoAdapters.scala` module handles conversion between proto and domain types:
+
+```scala
+// Phase 1: Records conversion (outbound only)
+def toProto(record: FiberRecord): ottochain.v1.FiberRecord = ...
+
+// Phase 2: Message conversion (inbound + outbound) - after PR #89
+def fromProto(msg: ottochain.v1.OttochainMessage): models.Transaction = ...
+```
+
+**Current status:** Phase 1 complete, Phase 2 planned post-fiber-engine migration.
+
+### Sequenced Trait Structural Gap
+
+Generated proto types have structural differences from hand-written Scala types:
+
+- **Generated:** `fiberId: String`, `targetSequenceNumber: Option[proto.FiberOrdinal]`  
+- **Domain models:** `fiberId: UUID`, `sequenceNumber: models.FiberOrdinal`
+
+The `Sequenced` trait cannot be directly implemented by generated types. ProtoAdapters bridges this gap during conversion.
+
+## Testing Strategy
+
+### Integration Tests
+
+`ScalaPBIntegrationTest.scala` verifies:
+1. **Compilation:** Generated types compile successfully
+2. **Mixin verification:** All message types extend `DataUpdate`  
+3. **Type safety:** Constructor and field access work correctly
+4. **Union types:** `OttochainMessage` oneof functionality
+
+**Coverage:** 6 message types tested (CreateStateMachine, TransitionStateMachine, ArchiveStateMachine, CreateScript, InvokeScript, OttochainMessage)
+
+### CI Integration
+
+Proto module included in CI pipeline:
+```bash
+sbt proto/compile proto/test
+```
+
+This ensures:
+- Proto definitions compile successfully
+- Generated types satisfy type constraints
+- Mixin injection works correctly
+- No regressions in proto → Scala conversion
+
+## Proto Definitions
+
+### Core Messages
+
+| Message | Purpose | Key Fields |
+|---------|---------|------------|
+| `CreateStateMachine` | Create new fiber | `fiber_id`, `definition`, `initial_data` |
+| `TransitionStateMachine` | Trigger state transition | `fiber_id`, `event_name`, `payload` |
+| `ArchiveStateMachine` | Archive fiber | `fiber_id`, `target_sequence_number` |
+| `CreateScript` | Create script fiber | `fiber_id`, `script_program`, `access_control` |
+| `InvokeScript` | Execute script method | `fiber_id`, `method`, `args` |
+| `OttochainMessage` | Union of all messages | `oneof message` |
+
+### Validation Rules
+
+Proto definitions include validation via protoc-gen-validate:
+- `fiber_id`: minimum length 1
+- `event_name`: minimum length 1  
+- `method`: minimum length 1
+
+## Development Workflow
+
+### Adding New Message Types
+
+1. **Define proto message** in `src/main/protobuf/ottochain/v1/messages.proto`
+2. **Add DataUpdate mixin** via `scalapb.message.extends` option
+3. **Add to union** in `OttochainMessage.oneof`  
+4. **Write integration test** in `ScalaPBIntegrationTest.scala`
+5. **Update ProtoAdapters** (if domain model exists)
+
+### Proto Schema Evolution
+
+**Field numbering policy:** 
+- Reserve ranges 1-100 for core fields
+- Reserve 101-200 for extensions
+- Never reuse field numbers
+- Document breaking changes in migration guide
+
+### Generated Code Inspection
+
+Generated Scala files are in `target/scala-2.13/src_managed/main/scalapb/`. 
+
+**Useful for debugging:**
+- Verify mixin inheritance
+- Check constructor signatures
+- Inspect validation logic
+- Understand union type structure
\ No newline at end of file
diff --git a/modules/proto/src/test/scala/xyz/kd5ujc/proto/ScalaPBIntegrationTest.scala b/modules/proto/src/test/scala/xyz/kd5ujc/proto/ScalaPBIntegrationTest.scala
index ad252ec9..6d93dcd9 100644
--- a/modules/proto/src/test/scala/xyz/kd5ujc/proto/ScalaPBIntegrationTest.scala
+++ b/modules/proto/src/test/scala/xyz/kd5ujc/proto/ScalaPBIntegrationTest.scala
@@ -4,7 +4,7 @@ import cats.effect.IO
 
 import io.constellationnetwork.currency.dataApplication.DataUpdate
 
-import ottochain.v1.{CreateStateMachine, TransitionStateMachine}
+import ottochain.v1._
 import weaver.SimpleIOSuite
 
 object ScalaPBIntegrationTest extends SimpleIOSuite {
@@ -43,4 +43,80 @@ object ScalaPBIntegrationTest extends SimpleIOSuite {
       expect(dataUpdate.isInstanceOf[DataUpdate])
     }
   }
+
+  test("Generated ArchiveStateMachine extends DataUpdate") {
+    IO {
+      val archiveSM = ArchiveStateMachine(
+        fiberId = "test-archive-id",
+        targetSequenceNumber = Some(FiberOrdinal(value = 42))
+      )
+
+      // This should compile successfully if DataUpdate mixin works
+      val dataUpdate: DataUpdate = archiveSM
+
+      expect(archiveSM.fiberId == "test-archive-id") &&
+      expect(archiveSM.targetSequenceNumber.exists(_.value == 42)) &&
+      expect(dataUpdate.isInstanceOf[DataUpdate])
+    }
+  }
+
+  test("Generated CreateScript extends DataUpdate") {
+    IO {
+      val createScript = CreateScript(
+        fiberId = "test-script-id",
+        scriptProgram = None,
+        initialState = None,
+        accessControl = Some(AccessControlPolicy())
+      )
+
+      // This should compile successfully if DataUpdate mixin works
+      val dataUpdate: DataUpdate = createScript
+
+      expect(createScript.fiberId == "test-script-id") &&
+      expect(createScript.accessControl.isDefined) &&
+      expect(dataUpdate.isInstanceOf[DataUpdate])
+    }
+  }
+
+  test("Generated InvokeScript extends DataUpdate") {
+    IO {
+      val invokeScript = InvokeScript(
+        fiberId = "test-invoke-id",
+        method = "execute",
+        args = None,
+        targetSequenceNumber = Some(FiberOrdinal(value = 10))
+      )
+
+      // This should compile successfully if DataUpdate mixin works
+      val dataUpdate: DataUpdate = invokeScript
+
+      expect(invokeScript.fiberId == "test-invoke-id") &&
+      expect(invokeScript.method == "execute") &&
+      expect(invokeScript.targetSequenceNumber.exists(_.value == 10)) &&
+      expect(dataUpdate.isInstanceOf[DataUpdate])
+    }
+  }
+
+  test("Generated OttochainMessage union extends DataUpdate") {
+    IO {
+      // Test with CreateStateMachine variant
+      val createSM = CreateStateMachine(
+        fiberId = "union-test-id",
+        definition = None,
+        initialData = None,
+        parentFiberId = None
+      )
+
+      val ottochainMessage = OttochainMessage(
+        message = OttochainMessage.Message.CreateStateMachine(createSM)
+      )
+
+      // This should compile successfully if DataUpdate mixin works
+      val dataUpdate: DataUpdate = ottochainMessage
+
+      expect(ottochainMessage.message.isCreateStateMachine) &&
+      expect(ottochainMessage.message.createStateMachine.exists(_.fiberId == "union-test-id")) &&
+      expect(dataUpdate.isInstanceOf[DataUpdate])
+    }
+  }
 }