Limit archive rollout reads to requested threads (#43494)

## Why

Archiving threads reads metadata from every active rollout, including unrelated compressed files.

## What changed

Add `RolloutReferenceIndex::scan_unarchived_threads` and use it when archiving. Filter canonical filenames by the requested thread IDs before reading contents, while retaining metadata-based ownership checks.

## Testing

Add tests covering reverted rollouts, requested descendants, compressed rollouts, exclusion of archived and unrelated files, and candidate ownership checks.

GitOrigin-RevId: a64f7fa25e5493ed20312f1d8216422752272bae

codex-rs/thread-store/src/local/archive_thread.rs

@@ -39,12 +39,15 @@ pub(super) async fn archive_threads(
         }
     }
     let _writer_guards = store.acquire_writer_locks(&lock_thread_ids).await?;
-    // Already-archived rollouts need no move. Avoid reading the entire archive on every request.
-    let reference_index = RolloutReferenceIndex::scan_unarchived(store.config.codex_home.as_path())
-        .await
-        .map_err(|err| ThreadStoreError::Internal {
-            message: format!("failed to scan thread rollout files: {err}"),
-        })?;
+    // Only inspect active files whose names belong to the threads being archived.
+    let reference_index = RolloutReferenceIndex::scan_unarchived_threads(
+        store.config.codex_home.as_path(),
+        &thread_ids,
+    )
+    .await
+    .map_err(|err| ThreadStoreError::Internal {
+        message: format!("failed to scan thread rollout files: {err}"),
+    })?;
 
     let parent_thread_id = thread_ids[0];
     let mut archived_thread_ids = Vec::new();