fix(web): restore reverted messages to composer

[amitray007]

What Changed

Reverted user messages now return to the composer with their images. If a draft is already present, it is saved to Stash first.

The live timeline also removes the reverted message once the server confirms the rewind.

Why

“Revert to this message” rewound the checkpoint, but left the selected message in the timeline and forced users to recreate the prompt before sending it again.

Closes #5685

UI Changes

Before	After

Interaction

bettershot_1786392103024.mp4

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Built with GPT-5.6-Sol through T3 Code.

Note

Restore reverted user message prompt and attachments into the composer

• When reverting a thread checkpoint, the user's original message prompt and image attachments are now fetched and written back into the composer after revert completes.
• deriveRevertedMessageContent strips review comment blocks and preview-annotation screenshots from the prompt before restoration; fetchRevertedMessageAttachmentBlob fetches attachment blobs with a 10-second abort timeout.
• The composer is disabled during revert preparation; attachments are deduplicated, capped at PROVIDER_SEND_TURN_MAX_ATTACHMENTS, and any existing stash or context attachments are cleared before writing.
• Toasts surface warnings for missing images, attachment overflow, stash/clear behavior, and stash failures.
• Turnless message retention in threadReducer is now bounded by the latest retained checkpoint instead of keeping all turnless messages unconditionally.
• Risk: blob URLs are created during draft preparation and must be revoked on cleanup; any fetch failure within the timeout marks that attachment as unavailable rather than blocking restoration.

^{Macroscope summarized a216c72.}

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Note

Medium Risk
Touches checkpoint revert UX and client-side message retention after thread.reverted, plus blob URL lifecycle for restored attachments. Failures are mostly soft (toasts / unavailable images), but incorrect retention or cleanup would affect timeline correctness and composer state.

Overview
Reverting a checkpoint now puts the selected user message back into the composer (editable text + images), so users can edit and resend instead of recreating the prompt.

Existing draft text/images are stashed first when possible; session-bound context (terminal/element/preview/review) is cleared because it cannot be safely reused after a rewind. Preview-annotation screenshots and review/context blocks are stripped from the restored prompt. Attachment blobs are fetched with a 10s abort timeout, deduped, and capped at the composer image limit, with toasts for missing/overflow images and stash/clear outcomes.

Separately, retainMessagesAfterRevert now drops turnless messages after the latest retained checkpoint, so the timeline actually removes the reverted prompt once the server confirms the rewind.

^{Reviewed by Cursor Bugbot for commit a216c72. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new feature for restoring reverted messages to the composer, including attachment fetching, draft stashing, and complex state management. Despite the 'fix' prefix, the ~670 lines of additions represent significant new user-facing capability that warrants human review.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit af4d49122a15121bd56b5a385e0d64db176d5ecd. Configure here.}

[amitray007]

Won't be able to maintain this PR anymore. Feel free to use the code if needed, using a personal fork going forward.