Session-scoped notes panel for Codex Desktop App (shared user/agent + private regions)

What variant of Codex are you using?

App

What feature would you like to see?

A session-scoped "Notes" panel in the Codex Desktop App with two regions:

1. Shared region — markdown, read/write by both user and agent. Auto-injected into the agent's system context every turn from durable host state, so it survives compaction by construction.
2. Private region — markdown, user-only. Never sent to the model. Pure UI scratchpad.

Behavior:

• Scoped to the thread/session; persists across app restarts and session resume.
• Shared region is delimited in the system prompt with clear tags (e.g. <session_notes>…</session_notes>) so the model knows what it is.
• A toggle to disable shared-region injection without deleting the content.
• Soft size cap (~2 KB) with a UI warning above the threshold.

Why this matters

In long sessions, instructions specific to this session — e.g. "always run the script with --flag X", "the task list for this PR is …", "the convention I just decided on for this thread" — get lost to compaction. They don't belong in AGENTS.md (project-permanent, committed) or in the existing memories feature (cross-session, currently read-only per #19195). There's no slot today for session-scoped, compaction-durable, dual user/agent read-write context.

The current workaround is a side scratchpad in Apple Notes or a markdown buffer in another window, with manual copy-paste back into the chat each time. That fixes "a place to write" but not auto-injection, agent write-back, or scoping.

Additional information

• Prior art in this repo: #12973 (closed) proposed a "Notes" tab for the web variant and was closed by a collaborator for insufficient upvotes — not on merits. This proposal is for the desktop app specifically and adds the user/agent read-write split plus the auto-injection mechanic that #12973 didn't specify.
• Distinct from existing memories (#19195, #13194): memories are cross-session and currently read-only (the model is told Never update memories. You can only read them.). Session notes would be session-scoped and writable from both sides — a different slot in the context-surface design space.
• Related discussion: #323 (Persistent Memory / Document Planning.md Strategies) describes the workaround pattern this would replace.
• Cross-platform parallel: the same proposal is filed at pingdotgg/t3code#2397 — useful if maintainers want to see how a sibling community is framing it.