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rose-ash/lib/persist/backend.sx
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persist: compaction — drop snapshotted prefix, monotonic seq + 11 tests
Backend now tracks last-seq as a monotonic high-water mark (survives
truncation) and exposes :truncate-through. compaction.sx: persist/compact
checkpoints then drops events with seq <= snapshot seq; should-compact?/
maybe-compact give an explicit every-N policy. Determinism: post-compaction
replay value == uncompacted full replay. Phase 3 complete, 76/76.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-06-06 18:42:06 +00:00

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; persist/backend — the injected storage protocol. Every facet (log, kv,
; snapshot) goes through a backend dict, never touching storage directly, so
; file/pg/ipfs-ref backends swap in unchanged. A backend is a dict of fns:
; {:append :read :last-seq :truncate-through
; :kv-get :kv-put :kv-delete :kv-has? :kv-keys}
; The in-memory backend is the test default. State is three dicts held in a
; closure and mutated with set!: logs (stream -> event list), seqs (stream ->
; last assigned seq — a monotonic high-water mark that survives compaction so
; truncating the log prefix never lets a future append reuse a seq), kv.
(define
persist/mem-backend
(fn
()
(let ((logs {}) (seqs {}) (kv {})) {:truncate-through (fn (stream n) (let ((cur (get logs stream))) (set! logs (assoc logs stream (filter (fn (e) (> (persist/event-seq e) n)) (if cur cur (list))))))) :kv-keys (fn () (keys kv)) :read (fn (stream) (let ((cur (get logs stream))) (if cur cur (list)))) :kv-has? (fn (key) (has-key? kv key)) :last-seq (fn (stream) (let ((s (get seqs stream))) (if s s 0))) :append (fn (stream event) (begin (let ((cur (get logs stream))) (set! logs (assoc logs stream (append (if cur cur (list)) event)))) (set! seqs (assoc seqs stream (persist/event-seq event))))) :kv-delete (fn (key) (set! kv (dissoc kv key))) :kv-put (fn (key val) (set! kv (assoc kv key val))) :kv-get (fn (key) (get kv key))})))
; protocol accessors — call a backend op by keyword
(define
persist/backend-append
(fn (b stream event) ((get b :append) stream event)))
(define persist/backend-read (fn (b stream) ((get b :read) stream)))
(define
persist/backend-last-seq
(fn (b stream) ((get b :last-seq) stream)))
(define
persist/backend-truncate
(fn (b stream n) ((get b :truncate-through) stream n)))
(define persist/backend-kv-get (fn (b key) ((get b :kv-get) key)))
(define persist/backend-kv-put (fn (b key val) ((get b :kv-put) key val)))
(define persist/backend-kv-delete (fn (b key) ((get b :kv-delete) key)))
(define persist/backend-kv-has? (fn (b key) ((get b :kv-has?) key)))
(define persist/backend-kv-keys (fn (b) ((get b :kv-keys))))