Architecture decision records

The choices that shaped quarantine, with the reasoning attached — so they are revisited deliberately, not re-litigated by accident. Each record states the context it was made in; if the context changes, supersede the record rather than editing history.

#	Decision	Status
0001	Atomicity by temp-dir + rename, not locks	Accepted
0002	A directory per record, not a JSONL file	Accepted
0003	Pickle-first serialization with a lossy fallback chain	Accepted
0004	Zero runtime dependencies	Accepted
0005	Poison items derived from attempts, not a stored flag	Accepted
0006	Observability through hooks, never an embedded server	Accepted
0007	Commit point for object-store backends	Accepted