feat(kernel): inject decision journal into stage context + wire repository

testing/replay/build.gradle

@@ -6,6 +6,7 @@ plugins {
 
 dependencies {
     testImplementation(project(":core:events"))
+    testImplementation(project(":core:journal"))
     testImplementation(project(":core:sessions"))
     testImplementation(project(":core:transitions"))
     testImplementation(project(":core:validation"))

testing/replay/src/test/kotlin/DecisionJournalReplayTest.kt

@@ -0,0 +1,50 @@
+import com.correx.core.events.events.EventMetadata
+import com.correx.core.events.events.NewEvent
+import com.correx.core.events.events.SteeringNoteAddedEvent
+import com.correx.core.events.events.TransitionExecutedEvent
+import com.correx.core.events.types.EventId
+import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.StageId
+import com.correx.core.events.types.TransitionId
+import com.correx.core.journal.DecisionJournalProjector
+import com.correx.core.journal.DecisionJournalRenderer
+import com.correx.core.journal.DefaultDecisionJournalReducer
+import com.correx.core.journal.DefaultDecisionJournalRepository
+import com.correx.core.sessions.projections.replay.DefaultEventReplayer
+import com.correx.infrastructure.persistence.InMemoryEventStore
+import kotlinx.coroutines.runBlocking
+import kotlinx.datetime.Clock
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+
+class DecisionJournalReplayTest {
+
+    private fun meta(sessionId: SessionId, id: String) =
+        EventMetadata(EventId(id), sessionId, Clock.System.now(), 1, null, null)
+
+    @Test
+    fun `journal replay is deterministic`(): Unit = runBlocking {
+        val sessionId = SessionId("s")
+        val store = InMemoryEventStore()
+        store.append(NewEvent(meta(sessionId, "steer"), SteeringNoteAddedEvent(sessionId, "use jwt")))
+        store.append(
+            NewEvent(
+                meta(sessionId, "trans"),
+                TransitionExecutedEvent(sessionId, StageId("a"), StageId("b"), TransitionId("t")),
+            ),
+        )
+
+        val repo = DefaultDecisionJournalRepository(
+            DefaultEventReplayer(store, DecisionJournalProjector(DefaultDecisionJournalReducer())),
+        )
+        val renderer = DecisionJournalRenderer()
+
+        val a = renderer.render(repo.getJournal(sessionId))
+        val b = renderer.render(repo.getJournal(sessionId))
+
+        assertEquals(a, b)
+        assertTrue(a.contains("use jwt"))
+        assertTrue(a.contains("a → b"))
+    }
+}