[Bug]: unified search: "person" from Contacts is ignored

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Unified Search permits to select a "Person", and Contacts exposes an integration to list all contacts in the menu. This is useful (is supposed to be useful) in particular for Mail, but just doesn't work.

Steps to reproduce

1. have both Contacts and Mail apps
2. have some actual email and related contacts
3. open the Unified Search, and select as "Person" one of the contacts related to mails
4. do a search

Expected behavior

I obtain emails having the selected person in from, to or cc.

Nextcloud Server version

34

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.4

Web server

Nginx

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Enabled:
  - contacts: 8.8.0-dev.0
  - contactsinteraction: 1.15.0
  - dav: 1.39.0

Nextcloud Signing status

Nextcloud Logs

{
    "ocs": {
        "meta": {
            "status": "failure",
            "statuscode": 400,
            "message": ""
        },
        "data": "User f9497589-8cf1-4c78-9499-0dad0aeec270 not found"
    }
}

Additional info

OC\Search\FilterFactory handles all "person" as local Users, trying to retrieve them from IUserManager.

My guess is that it is missing some level of integration between Contacts and SearchComposer: contacts are listed among selectable people in the UI, but are not retrieved back while building the SearchQuery.

Start with OC\Search\FilterFactory and SearchComposer, then reproduce the problem with Contacts and Mail enabled and a contact linked to an email. Trace how the selected “person” value is handled when building the SearchQuery. Done means selecting a Contacts person returns matching Mail messages in from, to, or cc without the user-not-found error.