TC-15 only works if somebody else ran TC-14 first

Problem Description

Our regression pack is run by a rotating team in three timezones, and cases get picked up individually from a queue rather than run in order. TC-15 opens with "Continue with the booking created in TC-14", which means whoever draws it either has to find and run TC-14 first, or has to go looking for whatever booking the previous shift happened to leave behind.

Last cycle it was drawn by someone who did neither. She picked a booking from the list, changed a seat, and passed the case. We later found she had been on a fully flexible fare, which skips the part of the flow we actually wanted covered.

There is a second, slower failure. Nothing in the case ever gives the old seat back. Over a few months the good seats on the staging flight have been taken up one by one by past runs, and the step that says to choose a better seat now has almost nothing left to choose. The environment only rebuilds weekly.

We want a case that stands on its own, that covers the flow we intended, and that does not consume the environment a little more every time it runs.

Output Specification

Produce one markdown document at exactly manual/TC-15-seat-change-standalone.md containing:

1. A seat-change case that a tester can draw from the queue and run without having run, or found, anything else first.
2. Everything that must be true before the first step, using the bookings, flight and seats in the attached files - including which fare the case requires and why the tester must not substitute another.
3. The exact seat the passenger starts in and the exact seat they move to, plus for each step the single thing observed that decides pass or fail.
4. Whatever is needed so the case leaves the environment able to run it again next week.
5. A place to record failures.

Out of scope: rewriting TC-14, automating the case, and anything to do with check-in or boarding passes at the gate.

Input Files

Extract the following files before beginning.

=============== FILE: manual/TC-14-book.md ===============

TC-14 - Book a flight

1. Search VG204.
2. Pick a fare.
3. Enter passenger details.
4. Pay.
5. Check the confirmation.

=============== FILE: manual/TC-15-seat-change.md ===============

TC-15 - Change seat

Continue with the booking created in TC-14.

1. Open Manage booking.
2. Open the seat map.
3. Pick a better seat.
4. Confirm the change goes through.
5. Check the passenger is told.

=============== FILE: manual/test-data.md ===============

Staging booking data

Site: https://staging.vergo-air.example Manage-booking sign-in needs the booking reference plus the passenger's surname.

Seeded bookings on flight VG204, 14 Sep 2026, LHR-FCO

Seat changes are free on Economy Flex and Business. On Economy Light a seat change is chargeable and the passenger is taken through a card payment step (staging accepts test card 4111 1111 1111 1111, any future expiry, CVC 123).

Extra-legroom rows on VG204

Row 12 is the exit row. Current occupancy on staging:

Environment housekeeping

Staging is rebuilt from the reference data set every Sunday at 02:00 UTC. Between rebuilds nothing releases a seat automatically. The staging admin tool at /staging-admin/bookings has a "Revert booking to seeded state" action that restores a booking's original seat and clears any change fee; it takes a few seconds.

Notifications

Staging email is captured at https://staging.vergo-air.example/mailtrap and arrives within about two minutes. Seat-change confirmations quote the new seat and the flight number.