TASK
Prepare an architecture decision and first delivery slice for a booking business
expanding from one location to four. Write for its technical lead and operations manager.

CURRENT SYSTEM — FICTIONAL FACTS
[S1] One application and PostgreSQL database own room availability, reservations
and deposit references for Location A. Existing bookings must remain changeable.
As in the article, assume this system can keep serving A but cannot support the
new locations by their opening date.
[S2] A payment provider owns payment status. Its callbacks can arrive late or twice.
[S3] New locations B, C and D open in eight weeks. Staff use the system every day.
[S4] A reservation holds one room for a time interval. Two customers must not
confirm the same room for overlapping intervals.
[S5] There are two engineers. No shared customer-credit feature is required yet.

DECISION TO MAKE
Compare extending the current system, replacing it in one cutover, and moving
traffic by location. Recommend one approach under these constraints.

OUTPUT
1. A dependency and ownership map using S1–S5 as evidence.
2. An options table: continuity, consistency, delivery effort and reversibility.
3. A short decision record: context, choice, consequences and unresolved questions.
4. One implementable delivery slice with the state changes and interface contract.
5. A rollout and recovery plan that says who continues to service bookings created
after launch if new traffic is paused.

QUALITY BAR
Separate supplied facts from assumptions. Give each authoritative record one owner.
Explain concurrency and duplicate payment callbacks. Do not assume switching traffic
back copies new reservations into the old database. Do not deploy or contact anyone.