# Todo 53.1: EventPrompt Order Preservation

## Problem

Commit `cf481ab` correctly made EventPrompt derived state, but `removeEventPromptItems()` deletes it and `ensureEventPromptItem()` appends the replacement. Tool changes, mode round trips, and restored prompt lists therefore move EventPrompt to the end and change serialized system-message order.

## Scope

- Preserve the first generated EventPrompt's position relative to retained custom prompts.
- Remember that insertion position while `chat_agent_tools` hides EventPrompt.
- Restore the saved typed/legacy EventPrompt position when loading prompt items.
- Continue removing duplicate generated EventPrompt items and preserving ordinary custom prompts.
- Do not add frontend dependencies or change backend contracts.

## TDD Steps

1. Add a failing regression in `tests/test_websocket_api.py` that requires an explicit EventPrompt insertion-position state/helper, captures position before removal, and reinserts with `insertBefore` instead of unconditional append.
2. Run the focused test and confirm it fails for the current append-only implementation.
3. Implement the smallest position-preserving logic in `src/agent_lab/presentation/static/app.js`.
4. Verify tool refresh, `dual_agent -> chat_agent_tools -> dual_agent`, and restore paths use the same remembered position.
5. Run:

   ```bash
   uv run pytest tests/test_websocket_api.py -k "event_prompt or prompt_restore or tool_mode" -q
   node --check src/agent_lab/presentation/static/app.js
   git diff --check
   ```

6. Commit with the solved problem and ordering risk, then repeat spec and code-quality reviews.

## Acceptance

- EventPrompt content and visibility remain mode/tool-derived.
- At most one EventPrompt exists.
- Refreshing tools does not move EventPrompt.
- Hiding and showing EventPrompt restores its previous insertion position.
- Restoring typed or legacy prompt data derives the insertion position from the first generated EventPrompt while discarding duplicates.
- Custom prompt order and outbound request contracts remain unchanged.