Feature Request: Funnels - entity-scoped step matching by shared event property

Feature request

Is your feature request related to a problem?

When tracking a user's journey through our B2B SaaS, I want to know that events being sent all relate to the same object. Our software is eSigning. Our funnel goes document upload -> sent for signing -> signed. I want to be sure that when I track this funnel, the document that was created is the same as the document that was sent for signing is the same as the document that was signed. I can add the document_uuid as a property to all 3 events but then in the funnel I can't do anything with that.

Describe the solution you'd like

A setting in funnels to say that the user and some other property(s) must match for an event to be included.

Describe alternatives you've considered

PostHog AI suggested breakdown by document_uuid, which is too granular to properly read, and a SQL insight which is much harder to setup and can't be inspected interactively like the native funnels.

Additional context

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. Begin by finding the funnel configuration and event-matching implementation; completion should support requiring the user and one or more shared properties to match across steps, with the result usable in interactive funnels.