Block refcounting (atomic refs + condemned flag) lets live queries
survive concurrent compaction and retention. Levelled compactor merges
2h->8h->32h blocks via raw chunk passthrough. Retention drops blocks
older than the configured window. Background goroutine drives
flush/compact/retain cycles; exported RunCompaction/ApplyRetention allow
deterministic test control via injectable clock.
Soak test: 10k series x 48h simulated at 15s intervals (115M samples).
Validates flat memory (158 MiB peak), bounded disk (13 blocks), and zero
query errors during compaction.
All existing tests refactored to table-driven with uniform assertions.
Flush sealed head chunks to ULID-named block directories on disk. Each
block contains CRC'd chunk segment files (mmap'd for reads), a binary
index (symbol table, series, postings with TOC), and a meta.json written
last as the immutability gate. WAL is truncated after block fsync,
preserving the crash-safety ording invariant.
david