feat(research): dedicated SourceFetched + LowQualityExtraction events (D)

- promote research fetch quality + content_sha256 from ToolExecutionCompletedEvent
  metadata to first-class SourceFetchedEvent / LowQualityExtractionEvent (registered
  + serialization test); existing metadata write kept intact (additive)
- emitted from SandboxedToolExecutor on research-fetch tool completion, guarded on
  the url/content_sha256/quality markers; reuses the extractor's LOW_QUALITY marker

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

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

@@ -0,0 +1,41 @@
+package com.correx.core.events.events
+
+import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.StageId
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * A research T2 fetch completed and produced content at [contentSha256] (research-workflow-spec §3/§5).
+ *
+ * Promotes the fetch-quality + content-hash that previously lived only inside
+ * [ToolExecutionCompletedEvent] metadata into a first-class event, so "what sources were fetched"
+ * is queryable and renderable directly from the journal. Additive: the metadata write is retained
+ * for existing consumers. [quality] mirrors the extractor's quality marker as recorded in metadata.
+ */
+@Serializable
+@SerialName("SourceFetched")
+data class SourceFetchedEvent(
+    val sessionId: SessionId,
+    val stageId: StageId,
+    val url: String,
+    val contentSha256: String,
+    val quality: String,
+    val byteCount: Int = 0,
+) : EventPayload
+
+/**
+ * An extraction was retained but flagged low-quality — below the quality bar (research-workflow-spec §5)
+ * — for operator visibility. Emitted alongside [SourceFetchedEvent] when the fetch cleared rejection
+ * but fell under the minimum-content threshold (JS-rendered SPA, paywall); the content is still kept,
+ * the operator is simply warned that synthesis may want to route around it.
+ */
+@Serializable
+@SerialName("LowQualityExtraction")
+data class LowQualityExtractionEvent(
+    val sessionId: SessionId,
+    val stageId: StageId,
+    val url: String,
+    val contentSha256: String,
+    val reason: String,
+) : EventPayload

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

@@ -31,6 +31,7 @@ import com.correx.core.events.events.IdeaDiscardedEvent
 import com.correx.core.events.events.JournalCompactedEvent
 import com.correx.core.events.events.FileWrittenEvent
 import com.correx.core.events.events.L3MemoryRetrievedEvent
+import com.correx.core.events.events.LowQualityExtractionEvent
 import com.correx.core.events.events.InferenceCompletedEvent
 import com.correx.core.events.events.InitialIntentEvent
 import com.correx.core.events.events.InferenceFailedEvent
@@ -46,6 +47,7 @@ import com.correx.core.events.events.RepoMapComputedEvent
 import com.correx.core.events.events.RetryAttemptedEvent
 import com.correx.core.events.events.WorkspaceStateObservedEvent
 import com.correx.core.events.events.RiskAssessedEvent
+import com.correx.core.events.events.SourceFetchedEvent
 import com.correx.core.events.events.StageCheckpointFailedEvent
 import com.correx.core.events.events.StageCheckpointPassedEvent
 import com.correx.core.events.events.StageCompletedEvent
@@ -137,6 +139,8 @@ val eventModule = SerializersModule {
         subclass(StageCheckpointPassedEvent::class)
         subclass(StageCheckpointFailedEvent::class)
         subclass(PossibleContradictionFlaggedEvent::class)
+        subclass(SourceFetchedEvent::class)
+        subclass(LowQualityExtractionEvent::class)
     }
 }
 

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

@@ -0,0 +1,47 @@
+package com.correx.core.events.serialization
+
+import com.correx.core.events.events.EventPayload
+import com.correx.core.events.events.LowQualityExtractionEvent
+import com.correx.core.events.events.SourceFetchedEvent
+import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.StageId
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class ResearchSourceEventSerializationTest {
+
+    private val sessionId = SessionId("s")
+    private val stageId = StageId("st")
+
+    @Test
+    fun `SourceFetchedEvent round-trips as polymorphic EventPayload`() {
+        val sample: EventPayload = SourceFetchedEvent(
+            sessionId = sessionId,
+            stageId = stageId,
+            url = "https://example.com/a",
+            contentSha256 = "abc123",
+            quality = "OK",
+            byteCount = 4096,
+        )
+        val encoded = eventJson.encodeToString(EventPayload.serializer(), sample)
+        assertTrue(encoded.contains("\"type\":\"SourceFetched\""), "SerialName must be present: $encoded")
+        val decoded = eventJson.decodeFromString(EventPayload.serializer(), encoded)
+        assertEquals(sample, decoded)
+    }
+
+    @Test
+    fun `LowQualityExtractionEvent round-trips as polymorphic EventPayload`() {
+        val sample: EventPayload = LowQualityExtractionEvent(
+            sessionId = sessionId,
+            stageId = stageId,
+            url = "https://example.com/spa",
+            contentSha256 = "def456",
+            reason = "extracted 12 chars, below minimum 200",
+        )
+        val encoded = eventJson.encodeToString(EventPayload.serializer(), sample)
+        assertTrue(encoded.contains("\"type\":\"LowQualityExtraction\""), "SerialName must be present: $encoded")
+        val decoded = eventJson.decodeFromString(EventPayload.serializer(), encoded)
+        assertEquals(sample, decoded)
+    }
+}