fix(kernel): stop compaction self-deadlocking long runs on re-entrant artifact Mutex

JournalCompactionService and TierContextSummarizer wrapped their event emit
in artifactStore.flushBefore { }. But emit -> SqliteEventStore.append already
calls flushBefore internally, re-acquiring CasArtifactStore's non-reentrant
Mutex -> the coroutine parks forever (no CPU, no thread, no exception, no
terminal event). Only fires once the journal crosses the compaction threshold,
i.e. exactly on long runs.

Emit directly; append()'s own flushBefore still fsyncs artifacts before the
referencing event is persisted, so durability ordering is preserved. Adds a
regression test with a lock-holding fake store (the prior fake took no lock,
which is why the deadlock escaped tests).

Vikunja #244.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LG7sGEbVJQncHJtsbPFJZm

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

@@ -43,16 +43,18 @@ class JournalCompactionService(
         }
 
         val summaryArtifactId = artifactStore.put(summaryText.toByteArray(Charsets.UTF_8))
-        artifactStore.flushBefore {
-            emit(
-                JournalCompactedEvent(
-                    sessionId = sessionId,
-                    coversThroughSequence = throughSequence,
-                    summaryArtifactId = summaryArtifactId,
-                    lowSalienceOmittedCount = lowCount,
-                ),
-            )
-        }
+        // Emit directly, NOT inside flushBefore { }: append() already fsyncs artifacts before it
+        // persists the event, so wrapping the emit here re-acquires the (non-reentrant) artifact
+        // Mutex that flushBefore already holds → self-deadlock. Only surfaces on long runs, which
+        // are the ones that cross the compaction threshold.
+        emit(
+            JournalCompactedEvent(
+                sessionId = sessionId,
+                coversThroughSequence = throughSequence,
+                summaryArtifactId = summaryArtifactId,
+                lowSalienceOmittedCount = lowCount,
+            ),
+        )
         return true
     }
 }

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

@@ -48,17 +48,18 @@ class TierContextSummarizer(
         }
         val summaryText = summarize(prompt)
         val summaryArtifactId = artifactStore.put(summaryText.toByteArray(Charsets.UTF_8))
-        artifactStore.flushBefore {
-            emit(
-                ContextSummarizedEvent(
-                    sessionId = sessionId,
-                    coversThroughSequence = coversThroughSequence,
-                    summaryArtifactId = summaryArtifactId,
-                    tier = tier,
-                    entriesOmittedCount = freeformEntries.size,
-                ),
-            )
-        }
+        // Emit directly, NOT inside flushBefore { }: append() already fsyncs artifacts before it
+        // persists the event, so wrapping the emit here re-acquires the (non-reentrant) artifact
+        // Mutex that flushBefore already holds → self-deadlock (same bug as JournalCompactionService).
+        emit(
+            ContextSummarizedEvent(
+                sessionId = sessionId,
+                coversThroughSequence = coversThroughSequence,
+                summaryArtifactId = summaryArtifactId,
+                tier = tier,
+                entriesOmittedCount = freeformEntries.size,
+            ),
+        )
         return true
     }
 }

core/kernel/src/test/kotlin/com/correx/core/kernel/orchestration/JournalCompactionServiceTest.kt

@@ -9,6 +9,9 @@ import com.correx.core.journal.model.DecisionKind
 import com.correx.core.journal.model.DecisionRecord
 import com.correx.core.utils.TypeId
 import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withTimeout
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Assertions.assertFalse
 import org.junit.jupiter.api.Assertions.assertTrue
@@ -70,6 +73,30 @@ class JournalCompactionServiceTest {
         assertEquals(fixedArtifactId, event.summaryArtifactId)
     }
 
+    // Regression: append() flushes artifacts inside the SAME non-reentrant Mutex that flushBefore
+    // holds. If compaction wraps its emit in flushBefore, the emit->append->flushBefore re-acquires
+    // that Mutex and self-deadlocks. This store mirrors production locking so the deadlock is real;
+    // the fake above cannot catch it because its flushBefore takes no lock.
+    private fun reentrantHostileArtifactStore(): ArtifactStore = object : ArtifactStore {
+        val mutex = Mutex()
+        override suspend fun put(bytes: ByteArray) = fixedArtifactId
+        override suspend fun get(id: TypeId): ByteArray? = null
+        override suspend fun flushBefore(commit: suspend () -> Unit) = mutex.withLock { commit() }
+    }
+
+    @Test
+    fun `does not deadlock when emit re-enters the artifact store (as append does)`(): Unit = runBlocking {
+        val store = reentrantHostileArtifactStore()
+        val svc = JournalCompactionService(store, { "summary" }, tokenThreshold = { 100 })
+        val state = stateWithRecords(makeRecord(1, DecisionKind.INTENT))
+        // emit simulates SqliteEventStore.append: it flushes artifacts inside the store mutex.
+        withTimeout(2000) {
+            svc.compactIfNeeded(SessionId("s1"), state, renderedTokenEstimate = 500) {
+                store.flushBefore { /* persist event row */ }
+            }
+        }
+    }
+
     @Test
     fun `only HIGH-salience records are included in the summarize prompt`(): Unit = runBlocking {
         val capturedPrompts = mutableListOf<String>()