fix(kernel,server): evict per-session caches on workflow termination (#54)

Two unbounded per-session leaks that never released after a workflow ended:

- SessionOrchestrator.artifactContentCache (full file contents, keyed
  "<sessionId>:<path>") grew for the process lifetime. Added
  evictArtifactContentCache(sessionId) — session-prefix key removal,
  rehydrate-safe — called on both completeWorkflow and failWorkflow.
  cancellations was already evicted on both terminal paths.

- NarrationSubscriber leaked a Channel + worker coroutine + lanes map entry
  per session forever. closeLane() now closes the lane channel on
  WorkflowCompleted/WorkflowFailed (draining the terminal narration first);
  the worker self-removes from lanes when its for-loop exits on close.

Deferred: SqliteEventStore.subscriptions eviction — removing the SharedFlow
mid-life would strand LiveArtifactRepository's downstream collector (a
suspended-coroutine leak worse than the tiny empty-SharedFlow entry).

Green: :core:kernel compile+detekt, :apps:server *NarrationSubscriber* (8).

apps/server/src/main/kotlin/com/correx/apps/server/narration/NarrationSubscriber.kt

@@ -104,7 +104,8 @@ class NarrationSubscriber(
                     stageId = p.stageId.value,
                 ),
             )
-            is WorkflowCompletedEvent -> enqueue(
+            is WorkflowCompletedEvent -> {
+                enqueue(
                     sid,
                     NarrationTrigger(
                         kind = "workflow_completed",
@@ -112,7 +113,10 @@ class NarrationSubscriber(
                         stageId = p.terminalStageId.value,
                     ),
                 )
-            is WorkflowFailedEvent -> enqueue(
+                closeLane(sid)
+            }
+            is WorkflowFailedEvent -> {
+                enqueue(
                     sid,
                     NarrationTrigger(
                         kind = "workflow_failed",
@@ -120,6 +124,8 @@ class NarrationSubscriber(
                         stageId = p.stageId.value,
                     ),
                 )
+                closeLane(sid)
+            }
             // Surface the semantic reviewer's verdict conversationally instead of a raw findings
             // dump: the narrator turns "FAIL, 2 findings" into a plain-language explanation the
             // operator can act on. Only narrate when there's something to say (non-PASS or findings).
@@ -221,6 +227,13 @@ class NarrationSubscriber(
         lanes[sessionId.value]?.pendingPauses?.clear()
     }
 
+    /** Closes a terminated session's lane so its worker drains any buffered narration (the terminal
+     *  one enqueued just before this) and then exits, self-removing the lane from [lanes]. Without
+     *  this, every session leaks its channel + worker coroutine + map entry forever. */
+    private fun closeLane(sessionId: SessionId) {
+        lanes[sessionId.value]?.channel?.close()
+    }
+
     private fun startLane(sessionId: SessionId): SessionLane {
         val channel = Channel<QueuedNarration>(capacity = Channel.UNLIMITED)
         val lane = SessionLane(channel, used = 0)
@@ -249,6 +262,9 @@ class NarrationSubscriber(
                         )
                     }
             }
+            // Channel closed on workflow termination: drop the lane so it stops leaking. A later event
+            // for the same session (none expected post-terminal) would lazily start a fresh lane.
+            lanes.remove(sessionId.value)
         }
         return lane
     }

core/kernel/src/main/kotlin/com/correx/core/kernel/orchestration/SessionOrchestrator.kt

@@ -338,6 +338,14 @@ abstract class SessionOrchestrator(
      *  Used by DefaultSessionOrchestrator.step() to populate EvaluationContext.artifactContent. */
     protected val artifactContentCache: ConcurrentHashMap<String, String> = ConcurrentHashMap()
 
+    /** Drops a terminated session's cached artifact contents (the heaviest per-session state — full
+     *  file/JSON payloads). Safe: rehydrateArtifactContentCache rebuilds it from durable events if the
+     *  session is ever resumed. Called on WorkflowCompleted/WorkflowFailed. */
+    private fun evictArtifactContentCache(sessionId: SessionId) {
+        val prefix = "${sessionId.value}:"
+        artifactContentCache.keys.removeAll { it.startsWith(prefix) }
+    }
+
     /** Deterministic extraction/repair ladder for near-miss LLM artifact text (prose-wrapped JSON,
      *  code fences, trailing commas). Pure — recomputes on replay, records no events. */
     private val artifactExtractionPipeline = ArtifactExtractionPipeline()
@@ -3091,6 +3099,7 @@ abstract class SessionOrchestrator(
         correlateCritiqueOutcomes(sessionId)
         emit(sessionId, WorkflowCompletedEvent(sessionId, terminalStageId, stageCount, workflowId))
         cancellations.remove(sessionId)
+        evictArtifactContentCache(sessionId)
         return WorkflowResult.Completed(sessionId, terminalStageId)
     }
 
@@ -3134,6 +3143,7 @@ abstract class SessionOrchestrator(
             )
         }
         cancellations.remove(sessionId)
+        evictArtifactContentCache(sessionId)
         return WorkflowResult.Failed(sessionId, reason, retryExhausted)
     }