Support paginated thread forks (#35220)

## Why

`thread/fork` rejected threads using paginated history, so they could not use the same fork workflow as legacy threads.

## What changed

- Create paginated forks by referencing a frozen source-history prefix while persisting only child-owned records in the new rollout.
- Support latest, `lastTurnId`, and `beforeTurnId` boundaries, including inherited lineage, model-context reconstruction, interruption markers, and approval-reviewer inheritance.
- Make paginated reads and occurrence search traverse referenced history while excluding source records added after the fork.
- Coordinate fork preparation with archive and delete operations, and materialize compressed rollouts before they become fork references.

## Testing

Added app-server and thread-store coverage for boundary selection, active turns, inherited reads and search, compressed lineage, and concurrent source lifecycle operations.

GitOrigin-RevId: 66052d69517d7fb97a3b7817ab77a39c5ad995fd

codex-rs/core/src/codex_delegate.rs

@@ -49,6 +49,7 @@ use crate::mcp_tool_call::McpToolApprovalMetadata;
 use crate::mcp_tool_call::build_guardian_mcp_tool_review_request;
 use crate::mcp_tool_call::is_mcp_tool_approval_question_id;
 use crate::mcp_tool_call::mcp_approvals_reviewer;
+use crate::session::ForkPersistence;
 use crate::session::GitEnrichmentPolicy;
 use crate::session::SUBMISSION_CHANNEL_CAPACITY;
 use crate::session::SessionIo;
@@ -115,6 +116,7 @@ pub(crate) async fn run_codex_thread_interactive(
         extensions: Arc::clone(&parent_session.services.extensions),
         conversation_history,
         requested_history_mode: None,
+        fork_persistence: ForkPersistence::Copied,
         session_source: SessionSource::SubAgent(subagent_source.clone()),
         forked_from_thread_id,
         parent_thread_id: Some(parent_session.thread_id),