feat(context): overlay sibling-stage writes onto repo retrieval

Files written by earlier stages this session aren't in the session-start
repo map and were never embedded, so semantic retrieval is structurally
blind to them. Overlay each stage's FileWrittenEvent post-images as
deterministic hits (score 1.0) leading the semantic hits, deduped by path
— no reindex, no embed. Descriptors derive via the comment-free
sourcedesc describe() so agent-written content can't inject prose.

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

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

@@ -10,6 +10,7 @@ import com.correx.core.context.model.TokenBudget
 import com.correx.core.context.model.EntryRole
 import com.correx.core.events.events.ArtifactContentStoredEvent
 import com.correx.core.events.events.FileWrittenEvent
+import com.correx.core.events.events.RepoKnowledgeHit
 import com.correx.core.events.events.ArtifactCreatedEvent
 import com.correx.core.events.events.ArtifactRepairAttemptedEvent
 import com.correx.core.events.events.ArtifactRepairFailedEvent
@@ -227,6 +228,40 @@ internal suspend fun SessionOrchestrator.fileWrittenManifest(sessionId: SessionI
     }.trimEnd()
 }
 
+/**
+ * Files written earlier THIS session by OTHER stages, projected as deterministic retrieval hits so
+ * a successor stage discovers sibling output that the session-start repo map (a snapshot) can never
+ * contain and the embedder can't rank (it was never indexed). Latest post-image per path, capped,
+ * most-recent first; each carries the comment-free [describe] descriptor over its recorded CAS bytes
+ * (untrusted navigation; CAS hash authoritative). Score 1.0 — this is deterministic grounding, not
+ * cosine similarity — so it survives the retriever's floor and the useful-hit filter. The current
+ * stage's own writes are excluded (retry-repair state and the file-written manifest cover those).
+ * Pure projection over recorded events + CAS, replay-safe.
+ */
+internal suspend fun SessionOrchestrator.sessionWrittenHits(
+    sessionId: SessionId,
+    currentStageId: StageId,
+): List<RepoKnowledgeHit> {
+    val events = eventStore.read(sessionId)
+    val invToStage = events.mapNotNull { it.payload as? ToolInvocationRequestedEvent }
+        .associate { it.invocationId to it.stageId }
+    val latestWrites = events.mapNotNull { it.payload as? FileWrittenEvent }
+        .filter { it.postImageHash != null && invToStage[it.invocationId].let { s -> s != null && s != currentStageId } }
+        .groupBy { it.path }
+        .mapValues { (_, writes) -> writes.last() }
+    if (latestWrites.isEmpty()) return emptyList()
+    return latestWrites.values
+        .sortedByDescending { it.timestampMs }
+        .take(tuning.repoMapInjectTopK)
+        .mapNotNull { write ->
+            val hash = write.postImageHash ?: return@mapNotNull null
+            val descriptor = artifactStore.get(ArtifactId(hash))?.let { describe(write.path, it).render() }
+                ?.takeIf { it.isNotBlank() }
+            val text = if (descriptor != null) "${write.path}: $descriptor" else write.path
+            RepoKnowledgeHit(path = write.path, text = text, score = 1.0f)
+        }
+}
+
 internal suspend fun SessionOrchestrator.emitStageCheckpoint(
     sessionId: SessionId,
     stageId: StageId,

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

@@ -320,14 +320,23 @@ internal suspend fun SessionOrchestrator.buildContextualRepoEntries(
         return repoEntriesOrMapFloor(sessionId, recorded.hits, stagePrompt) + buildDocsCatalogEntry(sessionId)
     }
 
+    // Sibling-stage output written earlier this session isn't in the session-start repo map and was
+    // never embedded, so semantic retrieval is structurally blind to it. Overlay it as deterministic
+    // hits (score 1.0) that lead the semantic hits, deduped by path — no reindex, no embed.
+    val writtenHits = sessionWrittenHits(sessionId, stageId)
     val retriever = repoKnowledgeRetriever
-        ?: return buildRepoMapEntries(sessionId, stagePrompt) + buildDocsCatalogEntry(sessionId)
-    val hits = runCatching { retriever.retrieve(sessionId, stagePrompt, tuning.repoMapInjectTopK) }
-        .getOrElse { e ->
-            if (e is CancellationException) throw e
-            log.warn("repo-knowledge retrieval failed for stage {}: {}", stageId.value, e.message)
-            emptyList()
-        }
+    val semanticHits = if (retriever == null) {
+        emptyList()
+    } else {
+        runCatching { retriever.retrieve(sessionId, stagePrompt, tuning.repoMapInjectTopK) }
+            .getOrElse { e ->
+                if (e is CancellationException) throw e
+                log.warn("repo-knowledge retrieval failed for stage {}: {}", stageId.value, e.message)
+                emptyList()
+            }
+    }
+    val writtenPaths = writtenHits.mapTo(mutableSetOf()) { it.path }
+    val hits = writtenHits + semanticHits.filterNot { it.path in writtenPaths }
     // Record the raw retrieval for audit (a degenerate all-zero result is itself the signal that
     // the embedder is noop / the index is empty), but only useful hits ever reach the agent.
     if (hits.isNotEmpty()) emit(sessionId, RepoKnowledgeRetrievedEvent(sessionId, stageId, stagePrompt, hits))

testing/integration/src/test/kotlin/NeedsArtifactInjectionTest.kt

@@ -48,9 +48,18 @@ import com.correx.testing.fixtures.cyclePolicyMissingValidator
 import com.correx.testing.fixtures.inference.MockInferenceProvider
 import com.correx.testing.fixtures.transitions.TransitionFixtures
 import com.correx.testing.kernel.MockSessionEventReplayer
+import com.correx.core.approvals.Tier
 import com.correx.core.events.events.ArtifactCreatedEvent
 import com.correx.core.events.events.ArtifactValidatedEvent
+import com.correx.core.events.events.EventMetadata
+import com.correx.core.events.events.FileWrittenEvent
+import com.correx.core.events.events.NewEvent
+import com.correx.core.events.events.ToolInvocationRequestedEvent
+import com.correx.core.events.events.ToolRequest
+import com.correx.core.events.types.EventId
+import com.correx.core.events.types.ToolInvocationId
 import kotlinx.coroutines.runBlocking
+import kotlinx.datetime.Clock
 import org.junit.jupiter.api.Assertions.assertFalse
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
@@ -197,6 +206,67 @@ class NeedsArtifactInjectionTest {
         )
     }
 
+    /**
+     * Slice 6: a file written by an EARLIER stage this session must surface to a later stage as a
+     * deterministic retrieval hit (a "relevantFiles" entry naming the path), even with no embedder —
+     * the session-start repo map can't contain it and semantic retrieval never indexed it.
+     */
+    @Test
+    fun `file written by an earlier stage surfaces to a later stage as a relevant file`(): Unit = runBlocking {
+        val sessionId = SessionId("write-overlay-1")
+        val stageA = StageId("A")
+        val stageB = StageId("B")
+        val inv = ToolInvocationId("inv-A-1")
+        val siblingPath = "src/Sibling.kt"
+
+        // Seed stage A's write into the log before the run; sessionWrittenHits projects it for stage B.
+        listOf(
+            ToolInvocationRequestedEvent(
+                invocationId = inv, sessionId = sessionId, stageId = stageA,
+                toolName = "file_write", tier = Tier.T2,
+                request = ToolRequest(
+                    invocationId = inv, sessionId = sessionId, stageId = stageA,
+                    toolName = "file_write", parameters = mapOf("path" to siblingPath),
+                ),
+            ),
+            FileWrittenEvent(
+                invocationId = inv, sessionId = sessionId, path = siblingPath,
+                postImageHash = "deadbeef", preExisted = false, timestampMs = 1,
+            ),
+        ).forEach { payload ->
+            eventStore.append(
+                NewEvent(
+                    metadata = EventMetadata(
+                        eventId = EventId(java.util.UUID.randomUUID().toString()),
+                        sessionId = sessionId, timestamp = Clock.System.now(),
+                        schemaVersion = 1, causationId = null, correlationId = null,
+                    ),
+                    payload = payload,
+                ),
+            )
+        }
+
+        // stageC makes stageB non-terminal so stageB actually gets a context pack built (terminal
+        // stages are entered as end-markers without assembling context).
+        val stageC = StageId("C")
+        val graph = WorkflowGraph(
+            id = "write-overlay-graph",
+            stages = mapOf(stageA to StageConfig(), stageB to StageConfig(), stageC to StageConfig()),
+            transitions = setOf(
+                TransitionEdge(id = TransitionId("t1"), from = stageA, to = stageB, condition = { true }),
+                TransitionEdge(id = TransitionId("t2"), from = stageB, to = stageC, condition = { true }),
+            ),
+            start = stageA,
+        )
+        buildOrchestrator(InferenceFixtures.fixedRouter()).run(sessionId, graph, defaultConfig)
+
+        val relevant = capturedEntries.filter { it.sourceType == "relevantFiles" }
+        assertTrue(
+            relevant.any { it.content.contains(siblingPath) },
+            "Expected a relevantFiles entry naming $siblingPath, got: ${relevant.map { it.content }}",
+        )
+    }
+
     @Test
     fun `stage with empty needs adds no neededArtifact entries`(): Unit = runBlocking {
         val sessionId = SessionId("needs-test-2")