Port as-of, since, history, and with-dry-run from slateval

[maxweber]

Summary

Ports slateval's temporal features into dbval — the last functional delta between the two engines. After this merges, slateval's only remaining uniqueness is its storage adapter, which #8 already ports.

Stacked on #8 (slatedb-store); retarget after it merges. Stack: #6 ← #7 ← #8 ← this.

What's ported

• as-of — the value of the database at transaction t (squuid or instant). Implemented as a basis bound: same value, max-tx clamped to t.
• since — only datoms asserted after t (exclusive).
• history — all datom versions including retractions; :added distinguishes assert/retract.
• with-dry-run — speculative transactions. A perfect fit for the pending-overlay engine from Introduce dbval.store: pluggable tuple storage behind a protocol #7: the transaction runs normally, nothing commits, and the overlay stays on :db-after so reads see the speculative datoms. Chained dry-runs accumulate; a real transact against a speculative value throws.
• 5-element datom patterns ([?e :age ?a _ ?added]) binding the assert/retract flag, Datomic-style — history views need this to be useful.
• Accessors as-of-t/since-t, temporal-view?; temporal views are read-only (guarded in conn/with and transact-tx-data).

Adaptation to dbval's architecture

slateval marks views by associng namespaced keys onto its record DB; dbval's DB is an opaque deftype, so the markers are explicit fields (as-of-tx, since-tx, history?). The five inline per-index filter chains consolidate into tx-visibility-xform — plus a reverse variant slateval doesn't have, so rseek-datoms works correctly on temporal views too.

Bugfix found while porting (latent in slateval as well)

A since lower bound can orphan a retract by filtering out its add. datoms-filter's pairing logic assumed every retract directly follows its add, so an orphaned tombstone was emitted as a datom (since views showed retracted pre-window values) and could even swallow an unrelated preceding add. datoms-filter now never emits non-adds and never drops an add against an unrelated retract — with regression tests for both scenarios. slateval needs the same one-line-shaped fix.

Tests

• dbval.test.time-travel ported from slateval (as-of by squuid and by instant, since, history + 5-element patterns, dry-run visibility/chaining/guards) plus the two new since-with-retractions regressions. One portability fix: the instant-based as-of test needed a 5ms gap between transactions — SQLite commits fast enough for both txs to share a millisecond, which SlateDB's ~100ms commits masked.
• Full suite: 167 tests, 1068 assertions, 0 failures.
• Temporal features smoke-verified against the memory store as well (storage-agnostic).

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https://claude.ai/code/session_014dX8tTR4yFh5SyBGw3atpo