Migrate archive/unarchive to local ThreadStore (#17892)

# Summary
- implement local ThreadStore archive/unarchive operations
- implement local ThreadStore read_thread operation
- break up the various ThreadStore local method implementations into
separate files
- migrate app-server archive/unarchive and core archive fixture to use
ThreadStore (but not all read operations yet!)
- use the ThreadStore's read operation as a proxy check for thread
persistence/existence in the app server code
- move all other filesystem operations related to archive (path
validation etc) into the local thread store.

# Tests
- add dedicated local store archive/unarchive tests

codex-rs/core/src/agent/control_tests.rs

@@ -7,7 +7,6 @@ use crate::config::Config;
 use crate::config::ConfigBuilder;
 use crate::contextual_user_message::SUBAGENT_NOTIFICATION_OPEN_TAG;
 use assert_matches::assert_matches;
-use chrono::Utc;
 use codex_features::Feature;
 use codex_login::CodexAuth;
 use codex_protocol::AgentPath;
@@ -24,6 +23,9 @@ use codex_protocol::protocol::TurnAbortReason;
 use codex_protocol::protocol::TurnAbortedEvent;
 use codex_protocol::protocol::TurnCompleteEvent;
 use codex_protocol::protocol::TurnStartedEvent;
+use codex_thread_store::ArchiveThreadParams;
+use codex_thread_store::LocalThreadStore;
+use codex_thread_store::ThreadStore;
 use pretty_assertions::assert_eq;
 use tempfile::TempDir;
 use tokio::time::Duration;
@@ -1658,38 +1660,18 @@ async fn resume_agent_from_rollout_reads_archived_rollout_path() {
         .await
         .expect("child thread should exist");
     persist_thread_for_tree_resume(&child_thread, "persist before archiving").await;
-    let rollout_path = child_thread
-        .rollout_path()
-        .expect("thread should have rollout path");
-    let state_db = child_thread
-        .state_db()
-        .expect("thread should have state db handle");
-
     let _ = harness
         .control
         .shutdown_live_agent(child_thread_id)
         .await
         .expect("child shutdown should succeed");
-
-    let archived_root = harness
-        .config
-        .codex_home
-        .join(crate::ARCHIVED_SESSIONS_SUBDIR);
-    tokio::fs::create_dir_all(&archived_root)
+    let store = LocalThreadStore::new(codex_rollout::RolloutConfig::from_view(&harness.config));
+    store
+        .archive_thread(ArchiveThreadParams {
+            thread_id: child_thread_id,
+        })
         .await
-        .expect("archived root should exist");
-    let archived_rollout_path = archived_root.join(
-        rollout_path
-            .file_name()
-            .expect("rollout file name should be present"),
-    );
-    tokio::fs::rename(&rollout_path, &archived_rollout_path)
-        .await
-        .expect("rollout should move to archived path");
-    state_db
-        .mark_archived(child_thread_id, archived_rollout_path.as_path(), Utc::now())
-        .await
-        .expect("state db archive update should succeed");
+        .expect("child thread should archive");
 
     let resumed_thread_id = harness
         .control