Conversation-only rewind for all providers and non-Git projects

[rohan-patnaik]

T3 Code currently offers checkpoint-based revert where Git and native provider rollback are available. In a non-Git project, users cannot rewind the conversation to edit an earlier prompt.

I propose a separate conversation-only revert on user messages: keep messages before the selected prompt, restore that prompt and its attachments to the composer, and leave workspace files unchanged. A fresh provider session receives the retained visible conversation, so this works without native rollback in all six provider adapters. The existing files-and-conversation revert remains separate.

A local implementation is prepared on current main. Focused tests cover Git/non-Git projects, provider reset failures, all six adapters, and shared client state. A real Codex UI test confirmed that discarded instructions no longer influence the new session and that the selected prompt is restored for editing.

Tradeoffs: this carries visible messages and attachment references, not hidden reasoning/tool state; retained history plus the next input must fit the existing 120,000-character input limit. I understand contributions are currently likely to be deferred and that this proposal does not imply an expectation of acceptance. I plan to link the implementation PR and UI evidence here for review.

Implementation assistance: GPT-6 through Codex.

[juliusmarminge]

Closing as a duplicate of #6882 — same ask: rewind/edit earlier conversation turns while leaving workspace files unchanged.

Please continue there (and link any implementation PR on that thread). Thanks!