Prevent expired invitations from silently failing and blocking future re-invites

[JoseSzycho]

What this changes

When someone lets a join invitation to an organization lapse, two things used to go wrong — and both could leave a person stuck in a situation they couldn't fix on their own:

1. Accepting a late invitation looked like it worked, but did nothing. If a person tried to accept an invitation after it had expired, the system recorded the acceptance without ever making them a member, and didn't tell them anything was wrong. They believed they had joined the organization, but they hadn't. The invitation just sat there as a dead record.

2. A dead invitation could block future invitations forever. Because any existing invitation — expired, declined, or otherwise finished — counted as a duplicate, an organization that wanted to invite the same person again was told "Duplicate value" and couldn't. One lapsed invitation could block a re-invite for good.

Why the bugs were there

Both symptoms came from the invite flow trusting an invitation's recorded state and never double-checking whether the invitation was still actually valid at the moment it was used:

• On acceptance, the system recorded the state without confirming the invitation was still live. When the invitation had already lapsed, the acceptance was recorded but the membership was never granted — silently.

• On re-invite, the duplicate check treated any existing invitation as a conflict, whether or not it was still live and pending. A rule meant to stop someone from being double-invited at the same time was also blocking legitimate fresh invitations once an older one had finished its life.

What we changed

• Accepting an expired invitation is now rejected with a clear message. The person is told the invitation has expired and they should ask for a new one — instead of a silent success that grants nothing.
• Only a live, pending invitation blocks a re-invite. An expired, declined, or otherwise finished invitation no longer stands in the way. An organization can invite a person again any time a previous invitation is no longer outstanding.
• An expired invitation never creates a membership. There is no backdoor path from an old acceptance record into a membership — the invitation must be valid at the moment it is used.

What else we improved

• A comprehensive end-to-end test suite now exercises the whole invitation lifecycle: accepting after expiry (must be rejected), re-inviting after expiry, re-inviting after a decline, blocking a genuine duplicate while an invitation is live, and the happy path where accepting a live invitation grants membership and removes the invitation.
• Every invitation's email is verified. The suite confirms the invitation email is actually created and addressed to the right person, so we know the invitee really was notified.
• Hardened the test infrastructure itself. While running the suite we found and fixed two test-side issues that could make the tests fail for the wrong reasons — an assertion that never matched, and test fixtures being picked up as a second, competing test run. The suite now runs cleanly and deterministically.

Outcome

No scenario leaves a person unable to join an organization. If an invitation lapses, the person gets a clear reason and the organization can simply invite them again. If an invitation is live, the person can accept it and become a member, exactly as they expect.

Closes #802

[JoseSzycho]

up!

[JoseSzycho]

@mattdjenkinson I see you updated the branch against main. The e2e tests are green ! 🚀