feat(acr): ACR Store 1 — content-hash observation cache for repo-file descriptors (#305)

Adds ObservationStore (core:context) keyed on (repoRoot, path), an in-memory default and
a durable SqliteObservationStore (infrastructure:persistence), and wires it into the two
SessionOrchestratorArtifacts call sites that re-derive a SourceDescriptor from CAS bytes
on every call — a hit on matching content hash skips both the CAS read and the regex
extraction. First slice of docs/plans/2026-07-21-acr-knowledge-accretion.md (build order:
observations before fixes/plan-shapes).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HMbPmZZjcXhR2crU82zZ8S

core/context/build.gradle

@@ -8,6 +8,8 @@ dependencies {
     implementation(project(":core:events"))
     implementation(project(":core:artifacts"))
     implementation(project(":core:sessions"))
+    testImplementation "org.jetbrains.kotlin:kotlin-test"
+    testImplementation "org.junit.jupiter:junit-jupiter"
 }
 
 tasks.named("koverVerify").configure { enabled = false }

core/context/src/main/kotlin/com/correx/core/context/observation/ObservationStore.kt

@@ -0,0 +1,36 @@
+package com.correx.core.context.observation
+
+import java.util.concurrent.ConcurrentHashMap
+
+/**
+ * ACR Store 1 (docs/plans/2026-07-21-acr-knowledge-accretion.md): a fact about a repo file,
+ * keyed on (repoRoot, path) — task-agnostic, any future run benefits. [contentHash] is the
+ * staleness check: a caller re-validates by hash before trusting [descriptorRender], per
+ * invariant #9 (never re-derive from a re-observed environment when the prior observation still
+ * holds). [descriptorRender] is [com.correx.core.sourcedesc.SourceDescriptor.render] output — the
+ * only thing every current call site actually consumes, so that's what's stored, not the object.
+ */
+data class Observation(
+    val repoRoot: String,
+    val path: String,
+    val contentHash: String,
+    val descriptorRender: String?,
+    val observedAtMs: Long,
+)
+
+interface ObservationStore {
+    suspend fun get(repoRoot: String, path: String): Observation?
+    suspend fun put(observation: Observation)
+}
+
+/** Default/test backend — process-lifetime only. Production wiring swaps in a durable store. */
+class InMemoryObservationStore : ObservationStore {
+    private val entries = ConcurrentHashMap<Pair<String, String>, Observation>()
+
+    override suspend fun get(repoRoot: String, path: String): Observation? =
+        entries[repoRoot to path]
+
+    override suspend fun put(observation: Observation) {
+        entries[observation.repoRoot to observation.path] = observation
+    }
+}

core/context/src/test/kotlin/com/correx/core/context/observation/InMemoryObservationStoreTest.kt

@@ -0,0 +1,43 @@
+package com.correx.core.context.observation
+
+import kotlinx.coroutines.runBlocking
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class InMemoryObservationStoreTest {
+
+    @Test
+    fun `put then get returns the stored observation`(): Unit = runBlocking {
+        val store = InMemoryObservationStore()
+        val obs = Observation("repoA", "src/Foo.kt", "hash1", "module=foo", 100L)
+
+        store.put(obs)
+
+        assertEquals(obs, store.get("repoA", "src/Foo.kt"))
+    }
+
+    @Test
+    fun `same path in different repos does not collide`(): Unit = runBlocking {
+        val store = InMemoryObservationStore()
+        store.put(Observation("repoA", "src/Foo.kt", "hashA", "a", 1L))
+        store.put(Observation("repoB", "src/Foo.kt", "hashB", "b", 2L))
+
+        assertEquals("hashA", store.get("repoA", "src/Foo.kt")?.contentHash)
+        assertEquals("hashB", store.get("repoB", "src/Foo.kt")?.contentHash)
+    }
+
+    @Test
+    fun `put overwrites the prior observation for the same key`(): Unit = runBlocking {
+        val store = InMemoryObservationStore()
+        store.put(Observation("repoA", "src/Foo.kt", "hash1", "old", 1L))
+        store.put(Observation("repoA", "src/Foo.kt", "hash2", "new", 2L))
+
+        assertEquals("hash2", store.get("repoA", "src/Foo.kt")?.contentHash)
+    }
+
+    @Test
+    fun `unknown key returns null`(): Unit = runBlocking {
+        assertNull(InMemoryObservationStore().get("repoA", "nope"))
+    }
+}

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

@@ -7,6 +7,7 @@ import com.correx.core.inference.Tokenizer
 import com.correx.core.journal.DefaultDecisionJournalRepository
 import com.correx.core.artifacts.kind.ArtifactKindRegistry
 import com.correx.core.artifactstore.ArtifactStore
+import com.correx.core.context.observation.ObservationStore
 import com.correx.core.events.events.ApprovalDecisionResolvedEvent
 import com.correx.core.events.events.ArtifactContentStoredEvent
 import com.correx.core.events.events.ClarificationAnswer
@@ -111,7 +112,8 @@ class DefaultSessionOrchestrator(
     readyTaskCounter: ReadyTaskCounter? = null,
     taskClaimCoordinator: TaskClaimCoordinator? = null,
     tuning: OrchestrationTuning = OrchestrationTuning(),
-) : SessionOrchestrator(repositories, engines, artifactStore, decisionJournalRepository, artifactKindRegistry = artifactKindRegistry, repoKnowledgeRetriever = repoKnowledgeRetriever, readyTaskCounter = readyTaskCounter, taskClaimCoordinator = taskClaimCoordinator, tuning = tuning), ApprovalGateway {
+    observationStore: ObservationStore? = null,
+) : SessionOrchestrator(repositories, engines, artifactStore, decisionJournalRepository, artifactKindRegistry = artifactKindRegistry, repoKnowledgeRetriever = repoKnowledgeRetriever, readyTaskCounter = readyTaskCounter, taskClaimCoordinator = taskClaimCoordinator, tuning = tuning, observationStore = observationStore), ApprovalGateway {
     override val tokenizer: Tokenizer? = tokenizer
     override val cancellations: ConcurrentHashMap<SessionId, AtomicBoolean> =
         ConcurrentHashMap<SessionId, AtomicBoolean>()

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

@@ -8,6 +8,7 @@ import com.correx.core.artifacts.kind.KindInference
 import com.correx.core.artifactstore.ArtifactStore
 import com.correx.core.context.builder.ContextPackBuilder
 import com.correx.core.context.model.ContextPack
+import com.correx.core.context.observation.ObservationStore
 import com.correx.core.events.events.ClarificationAnswer
 import com.correx.core.events.events.ClarificationAnsweredEvent
 import com.correx.core.events.events.ClarificationRequestedEvent
@@ -202,6 +203,7 @@ abstract class SessionOrchestrator(
     internal val readyTaskCounter: ReadyTaskCounter? = null,
     internal val taskClaimCoordinator: TaskClaimCoordinator? = null,
     internal val tuning: OrchestrationTuning = OrchestrationTuning(),
+    internal val observationStore: ObservationStore? = null,
 ) {
     internal val log = LoggerFactory.getLogger(this::class.java)
     internal val eventStore: EventStore = repositories.eventStore

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

@@ -207,6 +207,7 @@ internal suspend fun SessionOrchestrator.fileWrittenManifest(sessionId: SessionI
         .groupBy { it.path }
         .mapValues { (_, writes) -> writes.last() }
     if (latestWrites.isEmpty()) return null
+    val repoRoot = workspacePolicy?.workspaceRoot?.toString().orEmpty()
     return buildString {
         appendLine(
             "Files written by the producing stage. Each line gives the authoritative CAS image and a " +
@@ -215,9 +216,7 @@ internal suspend fun SessionOrchestrator.fileWrittenManifest(sessionId: SessionI
         )
         latestWrites.toSortedMap().forEach { (path, write) ->
             val hash = write.postImageHash ?: return@forEach
-            val descriptor = artifactStore.get(ArtifactId(hash))
-                ?.let { describe(path, it).render() }
-                ?.takeIf { it.isNotBlank() }
+            val descriptor = describeCached(repoRoot, path, hash)
             val stage = invToStage[write.invocationId]?.value
             append("- $path")
             stage?.let { append(" [by $it]") }
@@ -250,13 +249,13 @@ internal suspend fun SessionOrchestrator.sessionWrittenHits(
         .groupBy { it.path }
         .mapValues { (_, writes) -> writes.last() }
     if (latestWrites.isEmpty()) return emptyList()
+    val repoRoot = workspacePolicy?.workspaceRoot?.toString().orEmpty()
     return latestWrites.values
         .sortedByDescending { it.timestampMs }
         .take(tuning.repoMapInjectTopK)
         .mapNotNull { write ->
             val hash = write.postImageHash ?: return@mapNotNull null
-            val descriptor = artifactStore.get(ArtifactId(hash))?.let { describe(write.path, it).render() }
-                ?.takeIf { it.isNotBlank() }
+            val descriptor = describeCached(repoRoot, write.path, hash)
             val text = if (descriptor != null) "${write.path}: $descriptor" else write.path
             RepoKnowledgeHit(path = write.path, text = text, score = 1.0f)
         }

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

@@ -0,0 +1,35 @@
+package com.correx.core.kernel.orchestration
+
+import com.correx.core.context.observation.Observation
+import com.correx.core.events.types.ArtifactId
+import com.correx.core.sourcedesc.describe
+
+/**
+ * [describe]-and-render a written file's CAS bytes, short-circuited by ACR Store 1
+ * (docs/plans/2026-07-21-acr-knowledge-accretion.md) when a prior observation for this
+ * (repoRoot, path) already carries this exact content hash — skips both the CAS read and the
+ * regex extraction. Falls back to a fresh [describe] + records the result for next time. No-op
+ * (always fresh, never recorded) when no [SessionOrchestrator.observationStore] is wired.
+ */
+internal suspend fun SessionOrchestrator.describeCached(
+    repoRoot: String,
+    path: String,
+    hash: String,
+): String? {
+    val store = observationStore
+    val cached = store?.get(repoRoot, path)
+    if (cached != null && cached.contentHash == hash) return cached.descriptorRender
+    val rendered = artifactStore.get(ArtifactId(hash))
+        ?.let { describe(path, it).render() }
+        ?.takeIf { it.isNotBlank() }
+    store?.put(
+        Observation(
+            repoRoot = repoRoot,
+            path = path,
+            contentHash = hash,
+            descriptorRender = rendered,
+            observedAtMs = System.currentTimeMillis(),
+        ),
+    )
+    return rendered
+}