Crate turso_backup 

turso-backup — back up a local Turso (rewrite) database to S3-compatible object storage and restore it, with the at-rest artifact readable by vanilla SQLite.

Plan + findings: .yah/docs/working/turso-s3-backup.md

Three tiers (see modules), all three implemented:

• snapshot — Tier 1a: full VACUUM INTO snapshot → object store, behind a two-gate skip. snapshot::upload_base_snapshot publishes an image the caller already holds, for a caller that may not open the file itself.
• dedup — Tier 1b: incremental page-dedup snapshot.
• stream — Tier 2: WAL-frame streaming anchored to a 1a base, with restore by frame replay, an RPO watermark, two-level fencing, bounded spill backpressure (backpressure), one-puller-per-box fan-out (puller), and a stream::probe_conditional_puts preflight.

This header called tier 2 “deferred, engine-coupled” until 2026-08-28. It was neither by then: stream.rs had shipped in R005-F2/F3 and grown fencing (R732-F2), the RPO watermark (R574-T4) and frame batching (R761-F2). The claim was disproved by R760-F6 while wiring roadcase onto it, and corrected here rather than filed — a stale doc comment costs every reader after it the same wrong first impression.

@yah:relay(Q002, “Turso → S3 backup crate”) @yah:at(2026-05-26T22:28:29Z) @yah:kind(quest) @arch:see(.yah/docs/working/turso-s3-backup.md)

@yah:ticket(R003-T1, “Spike: decide crate shape (sibling vs wrapper) + name; pin deps (turso/object_store/anyhow/tokio); flesh skeleton”) @yah:assignee(agent:claude) @yah:at(2026-05-26T22:30:03Z) @yah:status(review) @yah:phase(P1) @yah:parent(R003) @arch:see(.yah/docs/working/turso-s3-backup.md) @yah:handoff(“Spike complete. Sibling crate (standalone, depends on turso via crates.io, no re-exports) >> wrapper — less coupling, simpler maintenance, matches how writer/ already depends on turso. Name confirmed: turso-backup.”) @yah:handoff(“Prior-art eval: tier 1a (VACUUM INTO + object_store) is greenfield-worthy — no crate wraps turso-rewrite snapshot to S3. smugglr/verneuil (page-dedup, tier 1b) and walrust/wal-backup (WAL streaming, tier 2) remain candidates per working doc for their respective phases; license-check deferrable to those spikes.”) @yah:handoff(“Deps pinned in Cargo.toml: turso 0.6.1, object_store 0.13, anyhow 1, tokio 1 (rt+macros). Skeleton modules fleshed: snapshot.rs has real BackupTarget struct + async signatures; dedup.rs/stream.rs use anyhow::Result. Crate compiles cleanly.”) @yah:next(“R003-F2: implement snapshot_and_upload (VACUUM INTO temp + object_store put + change_counter skip)”) @yah:next(“R003-F3: implement restore_latest (object_store get + write file)”) @yah:next(“R003-T4: green e2e in harness (writer -> snapshot sink -> MinIO -> restore -> verifier)”)

Modules

backpressure

Explicit R2 backpressure for the tier-2 WAL-frame drain loop (R574-F2).

claim

R850-F1: mints the fencing epoch stream::StreamConfig::epoch enforces, for callers with no raft state machine to ask. R850-F1 — store-side ownership claim: the fencing token an appliance can mint for itself, on the one authority both sides of a network cut can still reach.

dedup

Tier 1b — incremental page-dedup snapshot.

hydrate

R850-F1: hydrate-on-place — fill an empty volume’s declared databases from the store before the workload starts, under a claim. R850-F1 — hydrate-on-place: materialise a workload’s declared databases into an empty volume before the workload starts, under a fence.

puller

One-puller-per-box fan-out + warm applier (R574-F3).

snapshot

Tier 1a — full snapshot sink.

stream

Tier 2 — WAL-frame streaming sink (R005-F2).