[P3] Extract border research orchestration into a testable state machine #367

Priority

P3 - complex partial-failure behavior is concentrated in a large React hook without direct orchestration tests.

Finding

useBorderRollResearch coordinates two persistent stores, submission transport, AbortController lifecycle, sampling, finish, retry, reset, archive, and UI messages. borderRollSubmission similarly combines queue model, migration, storage, and HTTP.

Acceptance criteria

• Express queue and research transitions as a pure reducer or state machine outside React.
• Give storage and transport explicit injectable interfaces.
• Cover failure of each finish, send, archive, and retry step, including restart recovery.
• Keep the hook focused on mapping service state into React.