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Technical design doc

An RFC for an engineering change. Made from one message, so you can get your own in minutes.

Technical design doc

RFC-031: Lease-Based Reservations for Brindle Lockers

Context and problem

Brindle Lockers runs 2,400 smart parcel lockers across 310 sites. Today the carrier API writes a reservation row, and each cabinet controller polls `/v1/doors/state` every 5 seconds to learn which doors to open. Nothing prevents two carriers from claiming the same free door in the same polling window.

In March 2026 this produced 1,897 double-assignments out of 271,400 drops (0.7%). Each one triggers a support ticket and a manual re-route costing about $6.40. Polling also means a door-state change can take up to 5 seconds to appear in the customer app.

Goals and non-goals

Goals

• Guarantee at most one active reservation per door, enforced by the database.

• Cut door-state propagation to under 500 ms at p95.

• Reduce double-assignments to below 0.02% of drops.

An RFC for an engineering change

The prompt

Create a Doc technical design document for replacing Brindle Lockers' polling-based locker reservation sync with a lease-based Reservation Service and an event stream, so that no two parcels are ever assigned to the same locker door. Include context and problem, goals and non-goals, the proposed design with components and data flow, alternatives considered, API or schema changes in code blocks, rollout and migration plan, risks, and open questions.

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