feat(platform): add chat message editing and conversation branching

[larryro]

Summary

• Allow users to edit previously sent messages via a dialog, re-submitting the edited content as the latest version
• Introduce conversation branching: editing a message creates a new branch thread from that point, preserving the original conversation
• Add a branch navigator component for switching between alternate conversation branches, with selections persisted to thread metadata

Closes #1164

Test plan

• Send a message, then edit it — verify the edit dialog opens and re-submits correctly
• Edit a message mid-conversation — verify a new branch is created and the branch navigator appears
• Switch between branches using the navigator — verify messages update and selection persists across page reloads
• Edit multiple messages in different positions — verify navigators only show relevant branches
• Verify "edited" indicator appears on edited messages

Summary by CodeRabbit

• New Features
  • Added message editing capability—users can now edit their sent messages in conversations.
  • Introduced conversation branching—editing a message creates a new conversation branch, preserving the original thread.
  • Added branch navigation controls—users can switch between alternate conversation branches using previous/next buttons.
  • Added support for multiple conversation paths—track and navigate different responses to the same message edit.

[greptile-apps]

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[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

📝 Walkthrough

Walkthrough

This pull request implements a message editing feature with branching support for chat threads. It introduces frontend components (BranchNavigator, EditMessageDialog) and context management (BranchContext) for handling alternative conversation paths when users edit messages. The backend adds Convex operations (editAndBranch, createBranchThread) to create and manage branched threads, along with schema tables and queries for storing branch metadata. The chat interface is updated to track the active branch thread, preserve scroll position across branch switches, and expose edit actions on user messages. Database schema extensions support branch tracking and user selections. Internationalization strings are added for edit-related UI labels.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~75 minutes

Possibly related PRs

• feat(platform): persistent chat, scroll-intent, typewriter, and system message tags #836: Modifies scroll behavior in chat-interface.tsx (auto-scroll observers) which overlaps with the new branch-aware scroll-position preservation logic in this PR.
• feat(platform): refine chat streaming UX and simplify marker parser #511: Updates ChatMessagesProps and component structure in chat-messages.tsx, directly related to the prop additions and conditional rendering of branch navigation in this PR.
• feat: UI updates and automation enhancements #275: Extends the ChatMessage interface in use-message-processing.ts where this PR also adds the order field propagation for fork point tracking.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	All primary objectives from #1164 are addressed: message editing via dialog, re-submission of edited content, and branch navigation. An edited indicator was mentioned but not implemented in the code changes.	Implement and display an 'edited' indicator on messages that have been edited, as specified in the linked issue requirements.
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.57% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly summarizes the main changes: adding message editing and conversation branching features to the chat platform.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing message editing and conversation branching. No unrelated refactoring or scope creep detected.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/chat-message-edit-and-branch

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