Make thread store process-scoped (#19474)

- Build one app-server process ThreadStore from startup config and share
it with ThreadManager and CodexMessageProcessor.
- Remove per-thread/fork store reconstruction so effective thread config
cannot switch the persistence backend.
- Add params to ThreadStore create/resume for specifying thread
metadata, since otherwise the metadata from store creation would be used
(incorrectly).

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

@@ -3,7 +3,9 @@ use crate::CreateThreadParams;
 use crate::ThreadEventPersistenceMode;
 use crate::ThreadStoreError;
 use crate::ThreadStoreResult;
+use codex_protocol::protocol::ThreadMemoryMode;
 use codex_rollout::EventPersistenceMode;
+use codex_rollout::RolloutConfig;
 use codex_rollout::RolloutRecorder;
 use codex_rollout::RolloutRecorderParams;
 
@@ -11,9 +13,23 @@ pub(super) async fn create_thread(
     store: &LocalThreadStore,
     params: CreateThreadParams,
 ) -> ThreadStoreResult<RolloutRecorder> {
+    let cwd = params
+        .metadata
+        .cwd
+        .clone()
+        .ok_or_else(|| ThreadStoreError::InvalidRequest {
+            message: "local thread store requires a cwd".to_string(),
+        })?;
+    let config = RolloutConfig {
+        codex_home: store.config.codex_home.clone(),
+        sqlite_home: store.config.sqlite_home.clone(),
+        cwd,
+        model_provider_id: params.metadata.model_provider.clone(),
+        generate_memories: matches!(params.metadata.memory_mode, ThreadMemoryMode::Enabled),
+    };
     let state_db_ctx = store.state_db().await;
     let recorder = RolloutRecorder::new(
-        &store.config,
+        &config,
         RolloutRecorderParams::new(
             params.thread_id,
             params.forked_from_id,