Include shared histories in rollout compression (#42039)

## What changed

- Make `local_thread_store_compression` compress cold rollout files across shared and forked histories without a separate compression mode.
- Retire `local_thread_store_shared_compression` while continuing to accept it in strict configuration without changing compression behavior.
- Read rollout files through the compressed-rollout reader when `codex exec resume` determines the latest turn's working directory.

## Testing

- Cover compression and restoration of an archived fork chain.
- Cover cwd-based resume selection when only the compressed rollout remains.
- Cover the removed compatibility key in strict configuration.

GitOrigin-RevId: 8edebf61eccc1f79cabb8e641f8982c76f337bf1

codex-rs/core/src/thread_manager.rs

@@ -67,7 +67,6 @@ use codex_protocol::protocol::TurnAbortReason;
 use codex_protocol::protocol::TurnAbortedEvent;
 use codex_protocol::protocol::TurnEnvironmentSelection;
 use codex_protocol::protocol::W3cTraceContext;
-use codex_rollout::RolloutCompressionMode;
 use codex_rollout::state_db::StateDbHandle;
 use codex_skills_extension::HostSkillsService;
 use codex_thread_store::InMemoryThreadStore;
@@ -385,14 +384,6 @@ pub fn thread_store_from_config(
             let compression_enabled = config
                 .features
                 .enabled(Feature::LocalThreadStoreCompression);
-            let compression_mode = if config
-                .features
-                .enabled(Feature::LocalThreadStoreSharedCompression)
-            {
-                RolloutCompressionMode::IncludeShared
-            } else {
-                RolloutCompressionMode::Standalone
-            };
             let background_migration_enabled = config
                 .features
                 .enabled(Feature::BackgroundPaginatedRolloutMigration);
@@ -409,17 +400,11 @@ pub fn thread_store_from_config(
                         warn!("failed to migrate legacy rollouts on startup: {err}");
                     }
                     if compression_enabled {
-                        codex_rollout::spawn_rollout_compression_worker(
-                            codex_home,
-                            compression_mode,
-                        );
+                        codex_rollout::spawn_rollout_compression_worker(codex_home);
                     }
                 });
             } else if compression_enabled {
-                codex_rollout::spawn_rollout_compression_worker(
-                    config.codex_home.to_path_buf(),
-                    compression_mode,
-                );
+                codex_rollout::spawn_rollout_compression_worker(config.codex_home.to_path_buf());
             }
             store
         }