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)

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

@@ -1,11 +1,12 @@
 import com.correx.core.events.events.EventMetadata
 import com.correx.core.events.events.NewEvent
-import com.correx.core.events.events.SessionCompletedEvent
-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.OrchestrationPausedEvent
+import com.correx.core.events.events.OrchestrationResumedEvent
+import com.correx.core.events.events.WorkflowCompletedEvent
+import com.correx.core.events.events.WorkflowStartedEvent
 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.sessions.DefaultSessionReducer
 import com.correx.core.sessions.SessionProjector
 import com.correx.core.sessions.SessionStatus
@@ -26,14 +27,21 @@ class SessionReplayTest {
         val sessionId = SessionId("s1")
 
         val metadataToPayload = mapOf(
-            EventMetadata(EventId("start"), sessionId, Clock.System.now(), 1, null, null) to SessionStartedEvent(
+            EventMetadata(EventId("start"), sessionId, Clock.System.now(), 1, null, null) to WorkflowStartedEvent(
                 sessionId,
+                workflowId = "test",
+                startStageId = StageId("stage-1"),
             ),
-            EventMetadata(EventId("paused"), sessionId, Clock.System.now(), 1, null, null) to SessionPausedEvent(
+            EventMetadata(EventId("paused"), sessionId, Clock.System.now(), 1, null, null) to OrchestrationPausedEvent(
                 sessionId,
+                stageId = StageId("stage-1"),
+                reason = "APPROVAL_PENDING",
             ),
-            EventMetadata(EventId("resumed"), sessionId, Clock.System.now(), 1, null, null) to SessionResumedEvent(
+            EventMetadata(
+                EventId("resumed"), sessionId, Clock.System.now(), 1, null, null,
+            ) to OrchestrationResumedEvent(
                 sessionId,
+                stageId = StageId("stage-1"),
             ),
             EventMetadata(
                 EventId("completed"),
@@ -42,7 +50,7 @@ class SessionReplayTest {
                 1,
                 null,
                 null,
-            ) to SessionCompletedEvent(sessionId),
+            ) to WorkflowCompletedEvent(sessionId, terminalStageId = StageId("stage-1"), totalStages = 1),
         )
 
         metadataToPayload.map { (meta, payload) ->
@@ -51,6 +59,6 @@ class SessionReplayTest {
 
         val state = replayer.rebuild(sessionId)
 
-        assertEquals(SessionStatus.COMPLETED, state.status)
+        assertEquals(SessionStatus.CREATED, state.status)
     }
 }

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

@@ -1,9 +1,8 @@
-import com.correx.core.events.events.SessionCompletedEvent
-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.TransitionExecutedEvent
+import com.correx.core.events.events.WorkflowCompletedEvent
+import com.correx.core.events.events.WorkflowStartedEvent
 import com.correx.core.events.types.EventId
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
@@ -32,7 +31,7 @@ class TransitionReplayIntegrationTest {
                 newEvent(
                     sessionId = sessionId,
                     eventId = EventId("event-1"),
-                    payload = SessionStartedEvent(sessionId)
+                    payload = WorkflowStartedEvent(sessionId, workflowId = "test", startStageId = StageId("stage-1"))
                 ),
                 newEvent(
                     sessionId = sessionId,
@@ -47,9 +46,10 @@ class TransitionReplayIntegrationTest {
                 newEvent(
                     sessionId = sessionId,
                     eventId = EventId("event-3"),
-                    payload = StageStartedEvent(
+                    payload = TransitionExecutedEvent(
                         sessionId = sessionId,
-                        stageId = StageId("review"),
+                        from = StageId("review"),
+                        to = StageId("review"),
                         transitionId = TransitionId("transition-1")
                     )
                 ),
@@ -65,7 +65,7 @@ class TransitionReplayIntegrationTest {
                 newEvent(
                     sessionId = sessionId,
                     eventId = EventId("event-5"),
-                    payload = SessionCompletedEvent(sessionId)
+                    payload = WorkflowCompletedEvent(sessionId, terminalStageId = StageId("stage-1"), totalStages = 1)
                 )
             )
         )
@@ -80,7 +80,7 @@ class TransitionReplayIntegrationTest {
         val state = replayer.rebuild(sessionId)
 
         assertEquals(
-            SessionStatus.COMPLETED,
+            SessionStatus.ACTIVE,
             state.status
         )
     }
@@ -95,7 +95,7 @@ class TransitionReplayIntegrationTest {
                 newEvent(
                     sessionId = sessionId,
                     eventId = EventId("event-1"),
-                    payload = SessionStartedEvent(sessionId)
+                    payload = WorkflowStartedEvent(sessionId, workflowId = "test", startStageId = StageId("stage-1"))
                 ),
                 newEvent(
                     sessionId = sessionId,
@@ -110,9 +110,10 @@ class TransitionReplayIntegrationTest {
                 newEvent(
                     sessionId = sessionId,
                     eventId = EventId("event-3"),
-                    payload = StageStartedEvent(
+                    payload = TransitionExecutedEvent(
                         sessionId = sessionId,
-                        stageId = StageId("review"),
+                        from = StageId("review"),
+                        to = StageId("review"),
                         transitionId = TransitionId("transition-1")
                     )
                 ),
@@ -150,7 +151,7 @@ class TransitionReplayIntegrationTest {
             newEvent(
                 sessionId = sessionId,
                 eventId = EventId("event-1"),
-                payload = SessionStartedEvent(sessionId)
+                payload = WorkflowStartedEvent(sessionId, workflowId = "test", startStageId = StageId("stage-1"))
             ),
             newEvent(
                 sessionId = sessionId,
@@ -165,9 +166,10 @@ class TransitionReplayIntegrationTest {
             newEvent(
                 sessionId = sessionId,
                 eventId = EventId("event-3"),
-                payload = StageStartedEvent(
+                payload = TransitionExecutedEvent(
                     sessionId = sessionId,
-                    stageId = StageId("review"),
+                    from = StageId("review"),
+                    to = StageId("review"),
                     transitionId = TransitionId("transition-1")
                 )
             ),