lab(dr256): persist and reopen the existing OrderIndex (D-DRDT-SPLIT-1 S3) - #2020

S3 of dr-widefieldmask-dt-classview-v1.md §5. order_store writes the OrderIndex that OrderIndex::by_i32 builds to a file and reopens it as the same index. It has no sort of its own; on load it only checks the order.

What the file holds

• the permutation and the cached keys
• the key lane (KeyLane::Field(u8) or Computed(u64))
• the tie-break rule TIE_KEY_THEN_FRAME_POSITION: ascending key, then the row's position in the bound frame
• the table identity (class, population, rows), the mapping and source revisions, and the presence version

Refusals

attest refuses the reopened index when any of these changed: the table, the mapping, the key, the presence version, or the source content. The last one holds even when the mapping is unchanged, because an order index depends on content (EXO-255). from_bytes refuses a bad magic, an unknown layout, an unknown tie-break or key kind, a wrong length, a non-permutation, and keys out of order or ties out of frame-position order.

Evidence

• cargo test -p dr256-ternlog-lab: all suites pass, 17 of them in tests/order_store.rs. clippy -D warnings and fmt are clean.
• The expected sequences in the tests are hand-written literals. T1 and T2 compare the reopened index against the real by_i32 index: permutation, keys, between over five ranges, gt, and the prepare_order count.
• the_module_never_sorts asserts that the source contains no .sort.
• 19 disable runs, one per guard, each turned its test red. Each anchor was asserted to occur exactly once, and the file was restored afterwards. Examples:
  • the reversed write order and the reversed keys on reopen (T1, T2)
  • each attest guard short-circuited (T3–T7)
  • each from_bytes guard short-circuited (T8–T12)
  • the key-lane and origin checks in seal (T13, T14, T17)
  • the IO refusal mapped to another error (T15)
  • a .sort() added to the module (T16)

Not verified

• No timing was taken. Reopening reads the file once and verifies it in O(n).
• The real-path count checks use the lab's own fixtures only.

Generated by Claude Code