Codex sidebar: group conversation history by project before date

Summary

The new date-based conversation grouping (Today, Yesterday, Previous 7 Days, etc.) is useful, but applying it globally across all Codex conversations makes the sidebar increasingly difficult to navigate as thread volume grows.

Previously, project-scoped chats provided a natural hierarchy. With the current global timeline, conversations from every project are mixed together. Active projects generate enough threads that older conversations from other projects effectively disappear from normal navigation and often require search to find again.

Current behavior

The sidebar is effectively organized as:

Today
  ├─ Project A thread
  ├─ Project C thread
  ├─ Project A thread
  └─ Project B thread

Yesterday
  ├─ Project D thread
  ├─ Project A thread
  └─ Project C thread

At higher thread counts this becomes a single global feed. Older conversations are difficult to discover unless the user remembers enough about them to search.

Newly created/spawned threads can also be easy to lose in this global list, particularly when several Codex tasks or agents are active.

Suggested behavior

Keep the date grouping, but scope it to the selected project:

Project A

Today
  ├─ Thread 1
  ├─ Thread 2
  └─ Thread 3

Yesterday
  ├─ Thread 4
  └─ Thread 5

Previous 7 Days
  ├─ Thread 6
  └─ Thread 7

Older
  └─ View all...

In other words, the hierarchy should preferably be:

Project → Date → Threads

rather than:

Date → Threads from every project

A global/all-projects view could still exist as an optional view, and global search should continue to search across projects.

Why this matters

Codex conversations often map directly to codebases, features, bugs, experiments, and agent tasks. For users working across multiple repositories/projects, the project itself is the strongest navigation context.

A global chronological feed scales poorly because a highly active project pushes lower-activity project conversations out of view. The conversations still exist, but they become practically hidden behind search.

Search is useful as a fallback, but it should not become the primary mechanism for rediscovering older project work.

Additional suggestion

When a new thread or agent task is created within a project, it should immediately appear at the top of that project's Today section, even before it produces its first response. This would make spawned work much easier to track.

Overall, I like the new date grouping — I think retaining it while restoring project-level hierarchy would give the sidebar much better information architecture for users with a large number of Codex threads.