v0.7.8

Proves Parquet type fidelity end-to-end with four independent readers
(DuckDB, ClickHouse, pyarrow, BigQuery), emits native Parquet logical
types for UUID/JSON, and closes two validation-surface bugs uncovered
while walking the documented golden paths.

Types — native Parquet logical types + round-trip proof

• feat(types) — UUID columns now emit native Parquet
  LogicalType::Uuid as FixedSizeBinary(16) carrying the Arrow canonical
  arrow.uuid extension type; JSON/JSONB carry arrow.json. Downstream
  engines (DuckDB → native UUID, ClickHouse → Nullable(UUID),
  BigQuery) load these without a cast. Enabled via the parquet
  arrow_canonical_extension_types feature. See src/types/mapping.rs.
• test(types) — four-reader validator matrix: every PG/MySQL type
  round-trips through Parquet and is read back by DuckDB, ClickHouse,
  pyarrow, and (live) BigQuery to pin field metadata + row-group stats
  (tests/type_roundtrip/).
• fix(types/mysql) — UNSIGNED BIGINT (UINT64) overflows INT64;
  now mapped to Decimal128 so the full range survives.

Bug fixes — validation surface

• fix(pipeline/chunked) — the sequential checkpoint path ran
  --validate on every chunk file but never recorded the result, so
  mode: chunked + chunk_checkpoint: true + default parallel: 1 runs
  stored validated = NULL in export_metrics and dropped the
  validated: pass line from the run summary. It now sets the flag like
  the other three export paths (regression test in
  tests/live_chunked_recovery.rs).
• fix(preflight/doctor) — rivet doctor drops a .rivet_doctor_probe
  writability test object at the destination and never removes it. A
  subsequent rivet run --validate flagged it as an untracked_object
  and downgraded the run to validated: FAIL. The probe is now a
  recognised Rivet sidecar (manifest::DOCTOR_PROBE_FILENAME) and skipped
  by the manifest-aware --validate pass (regression test in
  src/pipeline/validate_manifest.rs).

Preflight + UX

• fix(preflight) — chunked / incremental exports on an indexed
  cursor / chunk column no longer report a false DEGRADED verdict. A
  catalog btree probe replaces the EXPLAIN-on-base-query heuristic, so
  an indexed PK reads as ACCEPTABLE with an (indexed) scan-type
  suffix.
• polish(ux) — rivet init explains its mode choice inline
  (# auto: ~N rows ≥ 100K threshold and chunk column 'id' is available)
  and scales chunk_size to the row estimate; skipped incremental runs
  print status: skipped (no new rows since cursor 'X'); the plaintext-
  password and TLS warnings fire from doctor / check; the retry-safe
  WARN is demoted to DEBUG for local destinations.

Docs + assets

• docs — validated every command in the user-facing guides against
  the binary; fixed drift (the file_log state table, real rivet doctor
  output, the pilot walkthrough's missing decimal(10,2) override).
• docs(gifs) — regenerated all instructional GIFs against current
  behavior (card UI, (indexed) scan type, validated: pass).

Dependencies

• Bumped mach2 0.4 → 0.6, tikv-jemallocator 0.6 → 0.7,
  criterion 0.5 → 0.8 (dev), brotli 8.0.2 → 8.0.3.