feat(router): enrich L2 decision points with steering and failure reason

Fix broken stage-summary interpolation ($payload.stageId rendered the event's toString()). RouterL2Entry gains reason + steeringNotes; the reducer folds SteeringNoteAddedEvent into pendingSteeringNotes and harvests them into the completing stage's L2 entry, then clears (adr-0003 §4, pure field extraction, zero inference). RouterContextBuilder renders summary + reason + steering.

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

@@ -214,7 +214,14 @@ class DefaultRouterContextBuilder(
     }
 
     private fun buildL2Content(l2Entry: RouterL2Entry): String {
-        return "Stage ${l2Entry.stageId.value} (${l2Entry.outcome}): ${l2Entry.summary}"
+        val base = "Stage ${l2Entry.stageId.value} (${l2Entry.outcome}): ${l2Entry.summary}"
+        val reason = l2Entry.reason?.let { " — reason: $it" }.orEmpty()
+        val steering = if (l2Entry.steeringNotes.isNotEmpty()) {
+            " | steering: " + l2Entry.steeringNotes.joinToString("; ")
+        } else {
+            ""
+        }
+        return base + reason + steering
     }
 
     private suspend fun buildContextEntry(

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

@@ -6,6 +6,7 @@ import com.correx.core.events.events.OrchestrationPausedEvent
 import com.correx.core.events.events.OrchestrationResumedEvent
 import com.correx.core.events.events.StageCompletedEvent
 import com.correx.core.events.events.StageFailedEvent
+import com.correx.core.events.events.SteeringNoteAddedEvent
 import com.correx.core.events.events.StoredEvent
 import com.correx.core.events.events.WorkflowCompletedEvent
 import com.correx.core.events.events.WorkflowFailedEvent
@@ -42,6 +43,7 @@ class DefaultRouterReducer : RouterReducer {
             is OrchestrationResumedEvent -> handleOrchestrationResumed(state)
             is StageCompletedEvent -> handleStageCompleted(state, event)
             is StageFailedEvent -> handleStageFailed(state, event)
+            is SteeringNoteAddedEvent -> handleSteeringNote(state, payload)
             is ChatTurnEvent -> handleChatTurn(state, event)
             is L3MemoryRetrievedEvent -> state.copy(lastRetrievedMemory = payload.hits)
             else -> state
@@ -87,12 +89,14 @@ class DefaultRouterReducer : RouterReducer {
         val payload = event.payload as StageCompletedEvent
         val entry = RouterL2Entry(
             stageId = payload.stageId,
-            summary = "Stage $payload.stageId completed",
+            summary = "Stage ${payload.stageId.value} completed",
             outcome = StageOutcomeKind.SUCCESS,
             timestamp = event.metadata.timestamp,
+            steeringNotes = state.pendingSteeringNotes,
         )
         return state.copy(
-            l2Memory = state.l2Memory + entry
+            l2Memory = state.l2Memory + entry,
+            pendingSteeringNotes = emptyList(),
         )
     }
 
@@ -100,16 +104,25 @@ class DefaultRouterReducer : RouterReducer {
         val payload = event.payload as StageFailedEvent
         val entry = RouterL2Entry(
             stageId = payload.stageId,
-            summary = "Stage $payload.stageId failed: ${payload.reason}",
+            summary = "Stage ${payload.stageId.value} failed",
             outcome = StageOutcomeKind.FAILURE,
             timestamp = event.metadata.timestamp,
+            reason = payload.reason,
+            steeringNotes = state.pendingSteeringNotes,
         )
         return state.copy(
             l2Memory = state.l2Memory + entry,
-            currentStageId = null
+            currentStageId = null,
+            pendingSteeringNotes = emptyList(),
         )
     }
 
+    // adr-0003 §4: harvest user steering into the current stage's decision point.
+    // Accumulate here; handleStageCompleted/Failed attach and clear. Pure field
+    // extraction from the event stream — no inference.
+    private fun handleSteeringNote(state: RouterState, payload: SteeringNoteAddedEvent): RouterState =
+        state.copy(pendingSteeringNotes = state.pendingSteeringNotes + payload.content)
+
     private fun handleChatTurn(state: RouterState, event: StoredEvent): RouterState {
         val payload = event.payload as ChatTurnEvent
         val turnRole = when (payload.role) {

core/router/src/main/kotlin/com/correx/core/router/model/RouterState.kt

@@ -34,6 +34,10 @@ data class RouterL2Entry(
     val summary: String,
     val outcome: StageOutcomeKind,
     val timestamp: Instant,
+    /** Failure reason, when [outcome] is FAILURE. */
+    val reason: String? = null,
+    /** User steering notes issued during this stage (adr-0003 §4 decision-point harvest). */
+    val steeringNotes: List<String> = emptyList(),
 )
 
 @Serializable
@@ -52,4 +56,9 @@ data class RouterState(
     val l2Memory: List<RouterL2Entry> = emptyList(),
     val conversationHistory: List<RouterTurn> = emptyList(),
     val lastRetrievedMemory: List<L3RetrievedHit> = emptyList(),
+    /**
+     * Steering notes accumulated during the current stage, harvested into the
+     * stage's [RouterL2Entry] when it completes or fails, then cleared.
+     */
+    val pendingSteeringNotes: List<String> = emptyList(),
 )