fix: complete all P2 audit findings — dead code, NPE guard, hygiene

P2-1: Guard SessionId NPE with safe-call in SessionsReducer
P2-2: Remove 16 dead event classes + reducer branches; replace with live orchestration events in tests
P2-3: Standardize ChatInput divergences — guard CancelSession, single-arg ProtocolError
P2-4: Remove dead TuiToolRecord.diff and ToolDisplayStatus.REQUESTED
P2-5: Remove dead streamLive from SessionEventBridge
P2-6: Extract SessionsReducerContext data class for 6+ param method
P2-7: Replace StageId("none") sentinel with TypeId.NONE
P2-9: Add TypeId.random() factory on all type-alias IDs
P2-10: Add KDoc on schemaVersion documenting reserved-for-migration
P2-8: Verified RouterReducer string-template already correct (TypeId value class toString)

core/artifacts/src/main/kotlin/com/correx/core/artifacts/ArtifactReducer.kt

@@ -1,11 +1,7 @@
 package com.correx.core.artifacts
 
 import com.correx.core.artifacts.model.ArtifactRelationship
-import com.correx.core.events.events.ArtifactArchivedEvent
 import com.correx.core.events.events.ArtifactCreatedEvent
-import com.correx.core.events.events.ArtifactRejectedEvent
-import com.correx.core.events.events.ArtifactRelationshipAddedEvent
-import com.correx.core.events.events.ArtifactSupersededEvent
 import com.correx.core.events.events.ArtifactValidatedEvent
 import com.correx.core.events.events.ArtifactValidatingEvent
 import com.correx.core.events.events.StoredEvent
@@ -25,23 +21,6 @@ class DefaultArtifactReducer : ArtifactReducer {
                 transition(state, ArtifactLifecyclePhase.VALIDATING, ArtifactLifecyclePhase.CREATED)
             is ArtifactValidatedEvent ->
                 transition(state, ArtifactLifecyclePhase.VALIDATED, ArtifactLifecyclePhase.VALIDATING)
-            is ArtifactRejectedEvent ->
-                transition(state, ArtifactLifecyclePhase.REJECTED, ArtifactLifecyclePhase.VALIDATING)
-            is ArtifactSupersededEvent ->
-                transition(state, ArtifactLifecyclePhase.SUPERSEDED, ArtifactLifecyclePhase.VALIDATED)
-            is ArtifactArchivedEvent ->
-                transitionFromAny(
-                    state,
-                    ArtifactLifecyclePhase.ARCHIVED,
-                    ArtifactLifecyclePhase.VALIDATED,
-                    ArtifactLifecyclePhase.REJECTED,
-                )
-            is ArtifactRelationshipAddedEvent -> {
-                val rel = ArtifactRelationship(p.sourceId, p.targetId, p.relationshipType)
-                Result.success(
-                    state.copy(lineage = state.lineage.copy(relationships = state.lineage.relationships + rel))
-                )
-            }
             else -> Result.success(state)
         }
 
@@ -59,19 +38,4 @@ class DefaultArtifactReducer : ArtifactReducer {
                 )
             )
         }
-
-    private fun transitionFromAny(
-        state: ArtifactState,
-        to: ArtifactLifecyclePhase,
-        vararg validFrom: ArtifactLifecyclePhase,
-    ): Result<ArtifactState> =
-        if (state.phase in validFrom) {
-            Result.success(state.copy(phase = to))
-        } else {
-            Result.failure(
-                IllegalStateException(
-                    "Invalid artifact transition: ${state.phase} → $to (expected one of ${validFrom.toList()})"
-                )
-            )
-        }
 }

core/context/src/main/kotlin/com/correx/core/context/DefaultContextReducer.kt

@@ -1,23 +1,8 @@
 package com.correx.core.context
 
 import com.correx.core.context.state.ContextState
-import com.correx.core.events.events.ContextBuildingFailedEvent
-import com.correx.core.events.events.ContextBuildingInterruptedEvent
-import com.correx.core.events.events.ContextBuildingStartedEvent
-import com.correx.core.events.events.ContextPackBuiltEvent
 import com.correx.core.events.events.StoredEvent
 
 class DefaultContextReducer : ContextReducer {
-    override fun reduce(state: ContextState, event: StoredEvent): ContextState =
-        when (val p = event.payload) {
-            is ContextBuildingStartedEvent -> state.copy(buildingInProgress = true, interrupted = false)
-            is ContextPackBuiltEvent -> state.copy(
-                buildingInProgress = false,
-                interrupted = false,
-                builtPackIds = state.builtPackIds + p.contextPackId,
-            )
-            is ContextBuildingFailedEvent -> state.copy(buildingInProgress = false, interrupted = false)
-            is ContextBuildingInterruptedEvent -> state.copy(buildingInProgress = false, interrupted = true)
-            else -> state
-        }
+    override fun reduce(state: ContextState, event: StoredEvent): ContextState = state
 }

core/events/src/main/kotlin/com/correx/core/events/events/ArtifactEvents.kt

@@ -1,7 +1,6 @@
 package com.correx.core.events.events
 
 import com.correx.core.events.types.ArtifactId
-import com.correx.core.events.types.ArtifactRelationshipType
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
 import kotlinx.serialization.SerialName
@@ -23,33 +22,6 @@ data class ArtifactValidatedEvent(
     val stageId: StageId,
 ) : EventPayload
 
-@Serializable
-@SerialName("ArtifactSuperseded")
-data class ArtifactSupersededEvent(
-    val artifactId: ArtifactId,
-    val supersededById: ArtifactId,
-    val sessionId: SessionId,
-    val stageId: StageId,
-) : EventPayload
-
-@Serializable
-@SerialName("ArtifactRelationshipAdded")
-data class ArtifactRelationshipAddedEvent(
-    val sourceId: ArtifactId,
-    val targetId: ArtifactId,
-    val relationshipType: ArtifactRelationshipType,
-    val sessionId: SessionId,
-) : EventPayload
-
-@Serializable
-@SerialName("ArtifactRejected")
-data class ArtifactRejectedEvent(
-    val artifactId: ArtifactId,
-    val sessionId: SessionId,
-    val stageId: StageId,
-    val reason: String,
-) : EventPayload
-
 @Serializable
 @SerialName("ArtifactCreated")
 data class ArtifactCreatedEvent(
@@ -58,11 +30,3 @@ data class ArtifactCreatedEvent(
     val stageId: StageId,
     val schemaVersion: Int,
 ) : EventPayload
-
-@Serializable
-@SerialName("ArtifactArchived")
-data class ArtifactArchivedEvent(
-    val artifactId: ArtifactId,
-    val sessionId: SessionId,
-    val stageId: StageId,
-) : EventPayload

core/events/src/main/kotlin/com/correx/core/events/events/ContextEvents.kt

@@ -1,62 +1,10 @@
 package com.correx.core.events.events
 
-import com.correx.core.events.types.ContextPackId
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
-@Serializable
-@SerialName("LayerTruncated")
-data class LayerTruncatedEvent(
-    val contextPackId: ContextPackId,
-    val layer: String,
-    val entriesDropped: Int,
-    val reason: String,
-) : EventPayload
-
-@Serializable
-@SerialName("ContextBuildingStarted")
-data class ContextBuildingStartedEvent(
-    val sessionId: SessionId,
-    val stageId: StageId,
-) : EventPayload
-
-@Serializable
-@SerialName("ContextBuildingFailed")
-data class ContextBuildingFailedEvent(
-    val sessionId: SessionId,
-    val stageId: StageId,
-    val reason: String,
-) : EventPayload
-
-// Emitted during replay when a session ended with buildingInProgress=true and no completion/failure event followed.
-@Serializable
-@SerialName("ContextBuildingInterrupted")
-data class ContextBuildingInterruptedEvent(
-    val sessionId: SessionId,
-    val stageId: StageId,
-) : EventPayload
-
-@Serializable
-@SerialName("CompressionApplied")
-data class CompressionAppliedEvent(
-    val contextPackId: ContextPackId,
-    val layer: String,
-    val entriesRemoved: Int,
-    val strategyApplied: String,
-) : EventPayload
-
-@Serializable
-@SerialName("ContextPackBuilt")
-data class ContextPackBuiltEvent(
-    val contextPackId: ContextPackId,
-    val sessionId: SessionId,
-    val stageId: StageId,
-    val budgetUsed: Int,
-    val budgetLimit: Int,
-) : EventPayload
-
 @Serializable
 @SerialName("SteeringNoteAdded")
 data class SteeringNoteAddedEvent(

core/events/src/main/kotlin/com/correx/core/events/events/EventMetadata.kt

@@ -12,6 +12,11 @@ data class EventMetadata(
     val eventId: EventId,
     val sessionId: SessionId,
     val timestamp: Instant,
+    /**
+     * Reserved for future event schema migration. Currently always hardcoded to `1`.
+     * No version-dispatch logic exists yet; this field is persisted for forward compatibility.
+     * When migration is needed, wire a version-aware deserialization path before bumping.
+     */
     val schemaVersion: Int,
     val causationId: CausationId?,
     val correlationId: CorrelationId?

core/events/src/main/kotlin/com/correx/core/events/events/SessionEvents.kt

@@ -4,41 +4,6 @@ import com.correx.core.events.types.SessionId
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
-@Serializable
-@SerialName("SessionStarted")
-data class SessionStartedEvent(
-    val sessionId: SessionId,
-    val initialContextId: String? = null
-) : EventPayload
-
-@Serializable
-@SerialName("SessionPaused")
-data class SessionPausedEvent(
-    val sessionId: SessionId,
-    val reason: String? = null
-) : EventPayload
-
-@Serializable
-@SerialName("SessionResumed")
-data class SessionResumedEvent(
-    val sessionId: SessionId,
-) : EventPayload
-
-@Serializable
-@SerialName("SessionCompleted")
-data class SessionCompletedEvent(
-    val sessionId: SessionId,
-    val summary: String? = null
-) : EventPayload
-
-@Serializable
-@SerialName("SessionFailed")
-data class SessionFailedEvent(
-    val sessionId: SessionId,
-    val errorCode: String? = null,
-    val errorMessage: String? = null
-) : EventPayload
-
 @Serializable
 @SerialName("ChatSessionStarted")
 data class ChatSessionStartedEvent(

core/events/src/main/kotlin/com/correx/core/events/events/StageEvents.kt

@@ -6,14 +6,6 @@ import com.correx.core.events.types.TransitionId
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
-@Serializable
-@SerialName("StageStarted")
-data class StageStartedEvent(
-    val sessionId: SessionId,
-    val stageId: StageId,
-    val transitionId: TransitionId
-) : EventPayload
-
 @Serializable
 @SerialName("StageCompleted")
 data class StageCompletedEvent(

core/events/src/main/kotlin/com/correx/core/events/serialization/Serialization.kt

@@ -4,39 +4,23 @@ import com.correx.core.events.events.ApprovalDecisionResolvedEvent
 import com.correx.core.events.events.ApprovalGrantCreatedEvent
 import com.correx.core.events.events.ApprovalGrantExpiredEvent
 import com.correx.core.events.events.ApprovalRequestedEvent
-import com.correx.core.events.events.ArtifactArchivedEvent
 import com.correx.core.events.events.ArtifactCreatedEvent
-import com.correx.core.events.events.ArtifactRejectedEvent
-import com.correx.core.events.events.ArtifactRelationshipAddedEvent
-import com.correx.core.events.events.ArtifactSupersededEvent
 import com.correx.core.events.events.ArtifactValidatedEvent
 import com.correx.core.events.events.ArtifactValidatingEvent
-import com.correx.core.events.events.CompressionAppliedEvent
-import com.correx.core.events.events.ContextBuildingFailedEvent
-import com.correx.core.events.events.ContextBuildingInterruptedEvent
-import com.correx.core.events.events.ContextBuildingStartedEvent
-import com.correx.core.events.events.ContextPackBuiltEvent
+import com.correx.core.events.events.ChatSessionStartedEvent
 import com.correx.core.events.events.EventPayload
 import com.correx.core.events.events.InferenceCompletedEvent
 import com.correx.core.events.events.InferenceFailedEvent
 import com.correx.core.events.events.InferenceStartedEvent
 import com.correx.core.events.events.InferenceTimeoutEvent
-import com.correx.core.events.events.LayerTruncatedEvent
 import com.correx.core.events.events.ModelLoadedEvent
 import com.correx.core.events.events.ModelUnloadedEvent
 import com.correx.core.events.events.OrchestrationPausedEvent
 import com.correx.core.events.events.OrchestrationResumedEvent
 import com.correx.core.events.events.RetryAttemptedEvent
 import com.correx.core.events.events.RiskAssessedEvent
-import com.correx.core.events.events.SessionCompletedEvent
-import com.correx.core.events.events.SessionFailedEvent
-import com.correx.core.events.events.ChatSessionStartedEvent
-import com.correx.core.events.events.SessionPausedEvent
-import com.correx.core.events.events.SessionResumedEvent
-import com.correx.core.events.events.SessionStartedEvent
 import com.correx.core.events.events.StageCompletedEvent
 import com.correx.core.events.events.StageFailedEvent
-import com.correx.core.events.events.StageStartedEvent
 import com.correx.core.events.events.SteeringNoteAddedEvent
 import com.correx.core.events.events.ToolExecutionCompletedEvent
 import com.correx.core.events.events.ToolExecutionFailedEvent
@@ -62,13 +46,7 @@ val eventModule = SerializersModule {
         subclass(ToolExecutionCompletedEvent::class)
         subclass(ToolExecutionFailedEvent::class)
         subclass(ToolExecutionRejectedEvent::class)
-        subclass(SessionStartedEvent::class)
-        subclass(SessionPausedEvent::class)
-        subclass(SessionResumedEvent::class)
-        subclass(SessionCompletedEvent::class)
-        subclass(SessionFailedEvent::class)
         subclass(SteeringNoteAddedEvent::class)
-        subclass(StageStartedEvent::class)
         subclass(StageFailedEvent::class)
         subclass(StageCompletedEvent::class)
         subclass(TransitionExecutedEvent::class)
@@ -76,19 +54,9 @@ val eventModule = SerializersModule {
         subclass(ApprovalDecisionResolvedEvent::class)
         subclass(ApprovalGrantCreatedEvent::class)
         subclass(ApprovalGrantExpiredEvent::class)
-        subclass(ContextBuildingStartedEvent::class)
-        subclass(ContextPackBuiltEvent::class)
-        subclass(CompressionAppliedEvent::class)
-        subclass(LayerTruncatedEvent::class)
-        subclass(ContextBuildingFailedEvent::class)
-        subclass(ContextBuildingInterruptedEvent::class)
         subclass(ArtifactCreatedEvent::class)
         subclass(ArtifactValidatingEvent::class)
         subclass(ArtifactValidatedEvent::class)
-        subclass(ArtifactRejectedEvent::class)
-        subclass(ArtifactSupersededEvent::class)
-        subclass(ArtifactArchivedEvent::class)
-        subclass(ArtifactRelationshipAddedEvent::class)
         subclass(InferenceFailedEvent::class)
         subclass(InferenceCompletedEvent::class)
         subclass(InferenceStartedEvent::class)

core/events/src/main/kotlin/com/correx/core/utils/TypeId.kt

@@ -1,6 +1,7 @@
 package com.correx.core.utils
 
 import kotlinx.serialization.Serializable
+import java.util.UUID
 
 @JvmInline
 @Serializable
@@ -11,4 +12,12 @@ value class TypeId(val value: String) {
     }
 
     override fun toString(): String = value
+
+    companion object {
+        /** Sentinel value used when no real stage/entity is available. */
+        val NONE = TypeId("none")
+
+        /** Create a new random ID using a UUID string. */
+        fun random(): TypeId = TypeId(UUID.randomUUID().toString())
+    }
 }

core/events/src/test/kotlin/com/correx/core/events/EventSerializationHardeningTest.kt

@@ -2,21 +2,20 @@ package com.correx.core.events
 
 import com.correx.core.approvals.ApprovalOutcome
 import com.correx.core.approvals.ApprovalStatus
-import com.correx.core.approvals.GrantScope
 import com.correx.core.approvals.Tier
 import com.correx.core.events.events.ApprovalDecisionResolvedEvent
-import com.correx.core.events.events.ContextPackBuiltEvent
 import com.correx.core.events.events.EventPayload
 import com.correx.core.events.events.OrchestrationPausedEvent
 import com.correx.core.events.events.RiskAssessedEvent
-import com.correx.core.events.events.SessionStartedEvent
+import com.correx.core.events.events.SteeringNoteAddedEvent
 import com.correx.core.events.events.ToolExecutionFailedEvent
+import com.correx.core.events.events.WorkflowCompletedEvent
+import com.correx.core.events.events.WorkflowStartedEvent
 import com.correx.core.events.risk.RiskAction
 import com.correx.core.events.risk.RiskLevel
 import com.correx.core.events.serialization.eventJson
 import com.correx.core.events.types.ApprovalDecisionId
 import com.correx.core.events.types.ApprovalRequestId
-import com.correx.core.events.types.ContextPackId
 import com.correx.core.events.types.RiskSummaryId
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
@@ -35,7 +34,6 @@ class EventSerializationHardeningTest {
     private val ts = Instant.parse("2026-01-01T00:00:00Z")
 
     private val payloads: List<Pair<String, EventPayload>> = listOf(
-        "SessionStarted" to SessionStartedEvent(sessionId = sessionId),
         "ToolExecutionFailed" to ToolExecutionFailedEvent(
             invocationId = ToolInvocationId("inv-1"),
             sessionId = sessionId,
@@ -51,12 +49,10 @@ class EventSerializationHardeningTest {
             resolutionTimestamp = ts,
             reason = null
         ),
-        "ContextPackBuilt" to ContextPackBuiltEvent(
-            contextPackId = ContextPackId("cp-1"),
+        "SteeringNoteAdded" to SteeringNoteAddedEvent(
             sessionId = sessionId,
+            content = "test steering note",
             stageId = stageId,
-            budgetUsed = 100,
-            budgetLimit = 4096
         ),
         "OrchestrationPaused" to OrchestrationPausedEvent(
             sessionId = sessionId,
@@ -69,7 +65,17 @@ class EventSerializationHardeningTest {
             riskSummaryId = RiskSummaryId("rs-1"),
             level = RiskLevel.MEDIUM,
             action = RiskAction.PROCEED
-        )
+        ),
+        "WorkflowStarted" to WorkflowStartedEvent(
+            sessionId = sessionId,
+            workflowId = "test-wf",
+            startStageId = stageId,
+        ),
+        "WorkflowCompleted" to WorkflowCompletedEvent(
+            sessionId = sessionId,
+            terminalStageId = stageId,
+            totalStages = 1,
+        ),
     )
 
     @Test
@@ -97,7 +103,7 @@ class EventSerializationHardeningTest {
 
     @Test
     fun `unknown fields in JSON are tolerated (ignoreUnknownKeys=true)`() {
-        val event = SessionStartedEvent(sessionId = sessionId)
+        val event = WorkflowStartedEvent(sessionId = sessionId, workflowId = "twf", startStageId = stageId)
         val json = eventJson.encodeToString(EventPayload.serializer(), event)
         val withExtra = json.replace("{", "{\"bogusField\":123,")
         assertDoesNotThrow {

core/router/src/main/kotlin/com/correx/core/router/RouterContextBuilder.kt

@@ -103,7 +103,7 @@ class DefaultRouterContextBuilder(
         return ContextPack(
             id = ContextPackId("${state.sessionId?.value ?: "unknown"}-router-pack"),
             sessionId = state.sessionId ?: SessionId("unknown"),
-            stageId = state.currentStageId ?: StageId("none"),
+            stageId = state.currentStageId ?: StageId.NONE,
             layers = layers,
             budgetUsed = budgetUsed,
             budgetLimit = budget.limit,

core/router/src/main/kotlin/com/correx/core/router/RouterFacade.kt

@@ -46,7 +46,7 @@ class DefaultRouterFacade(
         history.add(RouterTurn(role = TurnRole.USER, content = input, timestamp = Clock.System.now()))
 
         val stateWithHistory = state.copy(conversationHistory = history.toList())
-        val effectiveStageId = state.currentStageId ?: StageId("none")
+        val effectiveStageId = state.currentStageId ?: StageId.NONE
 
         val contextPack = routerContextBuilder.build(stateWithHistory, config.tokenBudget)
         val provider = inferenceRouter.route(effectiveStageId, setOf(ModelCapability.General))

core/sessions/src/main/kotlin/com/correx/core/sessions/DefaultSessionReducer.kt

@@ -1,13 +1,7 @@
 package com.correx.core.sessions
 
-import com.correx.core.events.events.SessionCompletedEvent
-import com.correx.core.events.events.SessionFailedEvent
-import com.correx.core.events.events.SessionPausedEvent
-import com.correx.core.events.events.SessionResumedEvent
-import com.correx.core.events.events.SessionStartedEvent
 import com.correx.core.events.events.StageCompletedEvent
 import com.correx.core.events.events.StageFailedEvent
-import com.correx.core.events.events.StageStartedEvent
 import com.correx.core.events.events.StoredEvent
 import com.correx.core.events.events.TransitionExecutedEvent
 
@@ -21,24 +15,9 @@ class DefaultSessionReducer : SessionReducer {
         val payload = event.payload
 
         val newStatus = when (payload) {
-
-            is SessionStartedEvent ->
-                SessionStatus.ACTIVE
-
-            is SessionPausedEvent ->
-                SessionStatus.PAUSED
-
-            is SessionResumedEvent ->
-                SessionStatus.ACTIVE
-
-            is SessionCompletedEvent ->
-                SessionStatus.COMPLETED
-
-            is SessionFailedEvent,
             is StageFailedEvent ->
                 SessionStatus.FAILED
 
-            is StageStartedEvent,
             is StageCompletedEvent,
             is TransitionExecutedEvent ->
                 SessionStatus.ACTIVE