FEAT: Improve chat usability

[Richard Lundeen (richlundeen)]

Description

This may not seem like much but I think it makes the chat window way more usable.

• Add Undo last send, keeping the converter placement and text so you can edit converter specifics in place.
• Make conversation editing and conversions more intuitive. Double clicking to edit, default same conversation, and a lot of little changes that are hard to see but very noticeable when using
• Make tests more reliable and reduce overlap.

Undo sits below the converter icon inside the prompt box. Screenshot uses demo data and mocked responses.

[Roman Lutz (romanlutz)]

[P2] Please preserve conversions on pieces that this edit did not touch. applied only contains conversions produced in this editor session, not every existing converted piece in converters.inputs. I reproduced this with one message containing two already-converted text pieces: opening its converter panel and editing the first working input clears the second piece's converted_value, type, and converter IDs. Saving then silently replaces that second piece's converted content with its original. Could this callback apply only the changed piece IDs, with explicit invalidation handled separately?

[Roman Lutz (romanlutz)]

[P2] Please preserve the pending prompt's original and conversion provenance on the round trip back to the composer. With this new composer-to-editor path, I reproduced: type hello, run Base64 conversion, enter Edit Conversation, Save, then Send. The outgoing piece is only { original_value: "aGVsbG8=" }; hello, converted_value, and applied_converter_ids are lost. draftMessageToInput flattens the conversion and restoreConversions(..., {}, {}) clears it. Restoring a real piece conversion rather than treating the converted output as a new original would keep the saved evidence accurate and retain the converter pipeline.

[Roman Lutz (romanlutz)]

[P2] Please also synchronize the composer when the edited draft no longer ends in a user message. The composer stays mounted and hidden during editing, and the save callback only updates it inside if (pendingPrompt). I reproduced typing a prompt, entering the editor, deleting that user message, and choosing Save to new attack: the deleted text immediately reappears in the composer. Changing that pending message's role to system has the same stale-draft problem. A successful save should clear or replace the composer from the edited result, while Cancel should retain the original draft.

[Roman Lutz (romanlutz)]

[P2] Please base this gate on replay support, not just native capability flags. supports_editable_history describes native support, while target.validate_history_replay() also accepts configured history adapters and provider restoration callbacks. I checked a real WebsocketTarget with conversation_restore_callback: the new backend replay preflight accepts user/assistant history, but its serialized capabilities still have supports_editable_history: false. This helper therefore disables repeats and branching and hides Undo for a target that can replay that history. Exposing the resolved replay capability from the backend would avoid duplicating a different capability policy in the UI.