# Todo 53.3: EventPrompt Payload Singleton

## Problem

The DOM refresh path removes duplicate generated EventPrompt items, but `collectSystemPrompts()` in `dual_agent` currently serializes every prompt item. A stale or user-edited custom item containing the complete generated EventPrompt signature can therefore be sent alongside the managed EventPrompt.

## Scope

- At the outbound collection boundary, discard generated-signature custom items in both invocation modes.
- In `dual_agent`, retain only the managed `event_agent_system` item plus ordinary custom prompts.
- In `chat_agent_tools`, retain ordinary custom prompts only and send no EventPrompt.
- Preserve prompt order and content for ordinary custom items.
- Do not alter restore, EventPrompt positioning, backend contracts, or UI layout.

## TDD Steps

1. Change the existing Node behavior test so `dual_agent` expects exactly one generated prompt instead of accepting a generated-signature custom duplicate.
2. Run the focused test and confirm RED against the current collector.
3. Apply the minimal filter in `collectSystemPrompts()`.
4. Verify ordinary custom prompts and managed EventPrompt order remain unchanged.
5. Run focused/full WebSocket tests, Node syntax, diff checks, and independent review.

## Acceptance

- `dual_agent` serializes ordinary custom prompts and at most one managed EventPrompt.
- `chat_agent_tools` serializes ordinary custom prompts and zero EventPrompt content.
- A generated-signature custom item cannot bypass the outbound boundary.
- EventPrompt visibility, ordering, restore deduplication, and tool-derived content remain unchanged.