[codex] Add rollback context duplication snapshot

[charley-oai]

What changed

• adds a targeted snapshot test for rollback with contextual diffs in codex_tests.rs
• snapshots the exact model-visible request input before the rolled-back turn and on the follow-up request after rollback
• shows the duplicate developer and environment context pair appearing again before the follow-up user message

Why

Rollback currently rewinds the reference context baseline without rewinding the live session overrides. On the next turn, the same contextual diff is emitted again and duplicated in the request sent to the model.

Impact

• makes the regression visible in a canonical snapshot test
• keeps the snapshot on the shared context_snapshot path without adding new formatting helpers
• gives a direct repro for future fixes to rollback/context reconstruction

[charley-oai]

This is the duplicate context bug 😢

[charley-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[charley-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".