page-db 0.5.0

The paging substrate beneath B-tree and heap storage engines - fixed-size pages, CRC32 headers with LSN slots, an LRU buffer pool with dirty-page pinning, and cross-platform Direct I/O.
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# page-db -- Roadmap

> Path from scaffold to a stable 1.0. Hard parts are front-loaded; each phase has hard exit criteria.
>
> **Anti-deferral rule:** no listed hard task moves to a later phase unless this file records the move and the reason.

---

## v0.1.0 -- Scaffold (DONE)

Compiles, CI green, structure correct, no domain logic.

- [x] Manifest, README, CHANGELOG, REPS, dual license, CI, deny, clippy, rustfmt, FUNDING.
- [x] API surface sketched in `docs/API.md`.

---

## v0.2.0 -- page format + header (CRC32C + LSN) + Direct I/O read/write (DONE)

Exit criteria:
- [x] Every public item has rustdoc + a runnable example.
- [x] Core invariants property-tested.

---

## v0.3.0 -- LRU buffer pool + pinning + dirty tracking (DONE)

Exit criteria:
- [x] New surface tested; hot paths benchmarked.
- [x] Pin/dirty invariants loom-checked.

---

## v0.4.0 -- page allocator / free-list + cross-platform Direct I/O hardening + feature freeze (DONE)

Exit criteria:
- [x] No `todo!`/`unimplemented!`. **Feature freeze declared** -- the public API
  is complete for 1.0; remaining 0.x work is hardening only.

---

## v0.5.0 -- torn-page / corruption fuzzing + alignment edge cases + API freeze (DONE)

Exit criteria:
- [x] **Public API frozen.** No additions before 1.0 -- only bug fixes and the
  on-disk-format freeze. Frozen surface: `PageFile`/`PageFileOptions`,
  `BufferPool`/`PageGuard`/`PageRef`/`PageMut`, `PageAllocator`, `PageStore`,
  `Page`, `PageId`/`Lsn`/`PageSize`, `PageError`/`PageResult`, `checksum`.
- [x] `cargo audit` + `cargo deny` clean.
- [x] Parse + recovery paths fuzzed (`fuzz/`: `page_parse`, `allocator_open`).
  Fuzzing fixed a corrupt-superblock DoS in the free-chain walk.

---

## v0.6.0 -> v1.0.0 -- Alpha / Beta / RC / Stable

Integrate against real consumers, broaden testing, capture final benchmarks, then freeze the public API until 2.0 and publish.

---

## Out of scope for 1.0

- B+tree or heap logic - that lives in `index-db` and the engines above.
- The write-ahead log itself - `wal-db` owns the WAL; page-db only reserves the LSN slot.
- Locking / concurrency control - that is `lock-db`.