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snapshot.sx: snapshot is a projection state {:value :seq} stored in kv under
snapshot/<name>. persist/checkpoint replays and saves; persist/replay folds
only the tail after the snapshot. Tests assert snapshot+tail == full replay
both ways + determinism. 65/65.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
115 lines
3.3 KiB
Plaintext
115 lines
3.3 KiB
Plaintext
; Phase 3 — snapshots + replay. Headline: snapshot + tail == full replay.
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(define snap-count (fn (acc e) (+ acc 1)))
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(persist-test
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"no snapshot loads fresh seed state"
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(persist/snapshot-load (persist/open) "feed" 0)
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{:value 0 :seq 0})
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(persist-test
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"snapshot-exists? false initially"
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(persist/snapshot-exists? (persist/open) "feed")
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false)
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(persist-test
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"checkpoint stores a snapshot"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/snapshot-exists? b "snap")))
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true)
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(persist-test
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"checkpoint value equals full projection"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(persist/project-value
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(persist/checkpoint b "s" "snap" snap-count 0))))
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3)
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(persist-test
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"checkpoint records the last seq"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(persist/project-seq
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(persist/checkpoint b "s" "snap" snap-count 0))))
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2)
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(persist-test
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"replay after checkpoint only folds the tail"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/append b "s" "x" 0 {})
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(persist/project-value
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(persist/replay b "s" "snap" snap-count 0))))
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3)
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(persist-test
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"snapshot + tail == full replay (value)"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(equal?
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(persist/project-value
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(persist/replay b "s" "snap" snap-count 0))
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(persist/project-fold b "s" snap-count 0))))
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true)
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(persist-test
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"snapshot + tail == full replay (whole state)"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/append b "s" "x" 0 {})
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(persist/append b "s" "x" 0 {})
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(equal?
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(persist/replay b "s" "snap" snap-count 0)
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(persist/project b "s" snap-count 0))))
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true)
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(persist-test
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"replay determinism: two replays from same snapshot agree"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/append b "s" "x" 0 {})
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(equal?
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(persist/replay b "s" "snap" snap-count 0)
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(persist/replay b "s" "snap" snap-count 0))))
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true)
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(persist-test
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"re-checkpoint advances the snapshot"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "snap" snap-count 0)
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(persist/project-seq (persist/snapshot-load b "snap" 0))))
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2)
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(persist-test
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"snapshots are keyed independently"
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(let
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((b (persist/open)))
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(begin
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(persist/append b "s" "x" 0 {})
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(persist/checkpoint b "s" "a" snap-count 0)
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(persist/snapshot-exists? b "b")))
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false)
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