Survey event triggers should fire in real-time, not for users who previously sent the event

Feature request

Is your feature request related to a problem?

Survey event triggers don't behave as real-time triggers. When I set a survey to show "when the user sends streak_extended", it also shows to users who fired that event in a previous session, even if they haven't fired it in the current session at all. The survey appears as soon as they open the app, not at the moment the event actually fires.

Describe the solution you'd like

Event-based survey triggers should be strictly real-time. A survey with an event trigger should only appear at the exact moment that event fires in the current session. Users who have previously fired the event in past sessions should not see the survey unless they fire the event again.

In other words: the event trigger should mean "show this survey right now because this event just fired," not "show this survey to anyone who has ever fired this event."

Describe alternatives you've considered

• Removing the event trigger and relying on manual posthog.renderSurvey() calls from the codebase, but this defeats the purpose of no-code survey targeting.
• Using person property filters as a workaround, but these are evaluated at session start rather than in real-time, so they have the same problem.

Additional context

This makes event-triggered surveys unreliable for moment-of-action feedback (e.g. showing a CSAT right after a user extends their streak). The current behavior undermines the core use case for event triggers.

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

No files, tests, or entry points are named. Start by locating the survey event-trigger evaluation path and its session/event handling, then verify that a survey appears only when the event fires in the current session and not merely when the user fired it previously.