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

infrastructure/src/main/kotlin/com/correx/infrastructure/InfrastructureModule.kt

@@ -53,8 +53,10 @@ import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
 import com.correx.infrastructure.router.turbovec.TurboVecL3MemoryStore
 import com.correx.infrastructure.router.turbovec.TurboVecSidecarConfig
+import com.correx.core.context.observation.ObservationStore
 import com.correx.infrastructure.persistence.SqliteEventStore
 import com.correx.infrastructure.persistence.artifact.LiveArtifactRepository
+import com.correx.infrastructure.persistence.observation.SqliteObservationStore
 import com.correx.infrastructure.tools.DefaultToolRegistry
 import com.correx.infrastructure.tools.DispatchingToolExecutor
 import com.correx.infrastructure.tools.SandboxedToolExecutor
@@ -106,6 +108,12 @@ object InfrastructureModule {
         )
     }
 
+    fun createObservationStore(dbPath: String = defaultDbPath): ObservationStore {
+        val dir = java.io.File(dbPath).parentFile
+        if (!dir.exists()) dir.mkdirs()
+        return SqliteObservationStore(DriverManager.getConnection("jdbc:sqlite:$dbPath"))
+    }
+
     fun createArtifactStore(rootDir: Path = Paths.get(defaultArtifactsRoot)): ArtifactStore {
         Files.createDirectories(rootDir)
         val index = SqliteArtifactIndex(rootDir.resolve("index.sqlite"))