feat(toolintent): record the session's active task as a session-local fact

Claiming a task now emits SessionWorkingTaskEvent{taskId, affectedPaths} into the
session's own stream (via a SessionFactRecorder port + event-store adapter), and
SessionContextProjection folds it into SessionContext.activeTask. So a gate learns
"which task is this session working, and its scope" by reading the session stream
— no cross-stream scan, no kernel->tasks dependency. Re-emitted on an affected_paths
edit by the claimant, so the snapshot scope stays current; latest wins on replay.

This is the data source the write-scope gate needs (next).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -1,6 +1,7 @@
 package com.correx.core.events.events
 
 import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.TaskId
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
@@ -10,6 +11,20 @@ data class ChatSessionStartedEvent(
     val sessionId: SessionId,
 ) : EventPayload
 
+/**
+ * Records, in the session's own stream, that this run claimed [taskId] and is working it with the
+ * declared [affectedPaths] write scope — a session-local fact so the gates know the active task
+ * without scanning task streams. Re-emitted when the claimant edits affected_paths, so the folded
+ * scope stays current; SessionContextProjection takes the most recent.
+ */
+@Serializable
+@SerialName("SessionWorkingTask")
+data class SessionWorkingTaskEvent(
+    val sessionId: SessionId,
+    val taskId: TaskId,
+    val affectedPaths: List<String> = emptyList(),
+) : EventPayload
+
 @Serializable
 @SerialName("SessionWorkspaceBound")
 data class SessionWorkspaceBoundEvent(

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

@@ -12,6 +12,7 @@ import com.correx.core.events.events.ArtifactValidatingEvent
 import com.correx.core.events.events.BriefEchoMismatchEvent
 import com.correx.core.events.events.BriefGroundingCheckedEvent
 import com.correx.core.events.events.ChatSessionStartedEvent
+import com.correx.core.events.events.SessionWorkingTaskEvent
 import com.correx.core.events.events.ClarificationAnsweredEvent
 import com.correx.core.events.events.ClarificationRequestedEvent
 import com.correx.core.events.events.ChatTurnEvent
@@ -139,6 +140,7 @@ val eventModule = SerializersModule {
         subclass(BriefEchoMismatchEvent::class)
         subclass(RiskAssessedEvent::class)
         subclass(ChatSessionStartedEvent::class)
+        subclass(SessionWorkingTaskEvent::class)
         subclass(ChatTurnEvent::class)
         subclass(RouterNarrationEvent::class)
         subclass(SessionWorkspaceBoundEvent::class)