Distributed Doubly Linked List (DDLL) order = fractional key + range-shard · 100K write + 100K read QPS · O(1) splice = single-row, single-shard insert, zero neighbor writes
arrows 0/15cards 9letters A–J
happy-path side-effect failure-comp new-infra
BOTE — canonical numbers (every N- chip in the rail links here)
Failure playbook (A–J)
What breaks first · interview framing