Redis priority ordering breaks for backlogs older than 115 days

[hemju]

Impact

Redis does not preserve strict priority ordering once an ENQUEUED backlog spans more than about 115.74 days. An old lower-priority job can sort ahead of a newer higher-priority job, unlike memory and PostgreSQL.

Root cause

RedisKeys.queueScore is -priority * 1e13 + enqueueMicros. A one-level priority difference is only 10^13 microseconds, so age eventually overwhelms priority.

Acceptance criteria

• Redis ordering exactly matches (priority DESC, id) for the complete supported priority and timestamp range.
• Preserve deterministic FIFO/tie behavior using the UUID member or an equivalent representation.
• Add a fixed-clock regression with jobs separated by more than 116 days.
• Update key-layout documentation and Lua/index consistency tests as needed.