feat(validation): artifact-emission repair ladder + empty-schema fix

Deterministic repair pipeline (extraction, classification, policy, gated
LLM-repair rung) with ArtifactRepairAttempted/Failed events. Also fix
JsonSchemaValidator: a schema with no declared properties describes 'any
object' — unknown-property enforcement now only applies against a declared
shape (empty-properties schemas were rejecting every real artifact).

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

@@ -50,3 +50,40 @@ data class ArtifactContentStoredEvent(
     val sessionId: SessionId,
     val stageId: StageId,
 ) : EventPayload
+
+/**
+ * A near-miss producer output was routed through the artifact-emission repair ladder. Only the
+ * nondeterministic rung (`rung = "LLM"`) is replay-relevant — the deterministic rungs recompute —
+ * but both are recorded for observability. See docs/specs/2026-07-04-artifact-emission-pipeline.md.
+ */
+@Serializable
+@SerialName("ArtifactRepairAttempted")
+data class ArtifactRepairAttemptedEvent(
+    val artifactId: ArtifactId,
+    val classification: String, // ArtifactFailure name
+    val rung: String,           // "DETERMINISTIC" | "LLM"
+    val sessionId: SessionId,
+    val stageId: StageId,
+) : EventPayload
+
+/** The repair ladder produced a schema-valid artifact. [contentHash] feeds the normal store path. */
+@Serializable
+@SerialName("ArtifactRepairResolved")
+data class ArtifactRepairResolvedEvent(
+    val artifactId: ArtifactId,
+    val contentHash: ArtifactId,
+    val sessionId: SessionId,
+    val stageId: StageId,
+) : EventPayload
+
+/** The repair ladder gave up; [decision] records the policy dispatch (retry/regenerate/abort/escalate). */
+@Serializable
+@SerialName("ArtifactRepairFailed")
+data class ArtifactRepairFailedEvent(
+    val artifactId: ArtifactId,
+    val classification: String,
+    val decision: String,
+    val reason: String,
+    val sessionId: SessionId,
+    val stageId: StageId,
+) : EventPayload

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

@@ -7,6 +7,9 @@ import com.correx.core.events.events.ApprovalGrantExpiredEvent
 import com.correx.core.events.events.ApprovalRequestedEvent
 import com.correx.core.events.events.ArtifactContentStoredEvent
 import com.correx.core.events.events.ArtifactCreatedEvent
+import com.correx.core.events.events.ArtifactRepairAttemptedEvent
+import com.correx.core.events.events.ArtifactRepairFailedEvent
+import com.correx.core.events.events.ArtifactRepairResolvedEvent
 import com.correx.core.events.events.ArtifactValidatedEvent
 import com.correx.core.events.events.ArtifactValidatingEvent
 import com.correx.core.events.events.BriefEchoMismatchEvent
@@ -120,6 +123,9 @@ val eventModule = SerializersModule {
         subclass(ApprovalGrantCreatedEvent::class)
         subclass(ApprovalGrantExpiredEvent::class)
         subclass(ArtifactContentStoredEvent::class)
+        subclass(ArtifactRepairAttemptedEvent::class)
+        subclass(ArtifactRepairResolvedEvent::class)
+        subclass(ArtifactRepairFailedEvent::class)
         subclass(ArtifactCreatedEvent::class)
         subclass(ArtifactValidatingEvent::class)
         subclass(ArtifactValidatedEvent::class)

core/events/src/test/kotlin/com/correx/core/events/serialization/ArtifactRepairEventSerializationTest.kt

@@ -0,0 +1,33 @@
+package com.correx.core.events.serialization
+
+import com.correx.core.events.events.ArtifactRepairAttemptedEvent
+import com.correx.core.events.events.ArtifactRepairFailedEvent
+import com.correx.core.events.events.ArtifactRepairResolvedEvent
+import com.correx.core.events.events.EventPayload
+import com.correx.core.events.types.ArtifactId
+import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.StageId
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ArtifactRepairEventSerializationTest {
+
+    private fun roundTrip(sample: EventPayload) =
+        assertEquals(sample, eventJson.decodeFromString(EventPayload.serializer(),
+            eventJson.encodeToString(EventPayload.serializer(), sample)))
+
+    @Test
+    fun `ArtifactRepairAttempted round-trips`() {
+        roundTrip(ArtifactRepairAttemptedEvent(ArtifactId("a"), "SCHEMA", "LLM", SessionId("s"), StageId("st")))
+    }
+
+    @Test
+    fun `ArtifactRepairResolved round-trips`() {
+        roundTrip(ArtifactRepairResolvedEvent(ArtifactId("a"), ArtifactId("hash"), SessionId("s"), StageId("st")))
+    }
+
+    @Test
+    fun `ArtifactRepairFailed round-trips`() {
+        roundTrip(ArtifactRepairFailedEvent(ArtifactId("a"), "UNSAFE", "Abort", "path escapes", SessionId("s"), StageId("st")))
+    }
+}