Add a 10-cell context usage graph status line item

Request

Please add an official status line item that renders context usage as a compact 10-cell graph in the TUI footer.

Suggested item id: context-graph

Suggested rendering:

[gpt-5.5 (1M context)] █░░░░░░░░░ 11%

Why

Codex already supports textual status line entries such as context-used, context-remaining, and context-window-size. A compact graph is easier to scan during long sessions and keeps the footer readable while still showing model/window context.

Proposed behavior

• Include model display name and compact context window size.
• Render a fixed 10-cell bar, rounded up per 10% bucket.
• Omit the item when context window information is unknown, matching existing context status line behavior.
• Make it selectable in the status line setup UI.

Prototype

I have a working fork/branch implementing this:

• Fork branch: https://github.com/k-kwen/codex/tree/feature/context-graph-status-line
• Commit: https://github.com/k-kwen/codex/commit/2ad2282ef

Targeted verification on upstream main:

cargo fmt -p codex-tui
cargo test -p codex-tui context_graph

Both passed locally.