Resolve lookup-refs via bounded AVET seeks, not full-index scans

[tiensonqin]

Summary

Lookup_refs.entity_id resolved lookup-refs by materializing visible_datoms (a whole-EAVT materialization + filter_pred pass) and then linearly scanning that list for the unique attr/value pair — a full-index scan per resolution. This routes direct resolution through bounded AVET seeks instead, matching upstream DataScript's indexed lookup.

Changes:

• Lookup_refs.context replaces the visible_datoms : db -> datom list field with entid : db -> attr -> value -> entity_id option; entity_id resolves through it (context.entid is wired to entid_db → find_avet_exact, a bounded PSet.slice on the (a, v) prefix plus duplicate_avet_by_attr). A shared entity_id_of_resolution helper factors the is_unique check + strict_missing error path, so entity_id and entity_id_in_datoms produce identical results/error messages.
• Tx-staging semantics are untouched: entity_id_in_datoms still scans the supplied datom list (entid_in_datoms over datoms), which is what staged-transaction paths call. This change is resolution-only.
• find_avet_exact now applies db.filter_pred to its bounded result set. This preserves the old visible_datoms filter behavior on filtered dbs (upstream FilteredDB also filters -datoms), and restores pre-5e3238a parity for entid on filtered dbs.
• Removed dead code: Transact_datoms.Make's visible_datoms context requirement and its entid helper (zero callers after 5e3238a), plus the now-unused visible_datoms alias in datascript.ml.

Before/after measurement (20k-block outliner db, 100k datoms, native exe on this VM — scratch bench, not committed):

lookup	before: entity_id via visible_datoms scan	after: bounded AVET seek
hit	~3.58 ms	~2.5 µs
miss	~3.59 ms	~2.1 µs

~1400× faster; scan range drops from the full 100k-datom index to a bounded attribute slice (~1 datom, unique attr). The new entity_id now costs the same as Datascript.entid (~2.3 µs), which already used find_avet_exact.

Tests: all 34 native test suites pass (test_lookup_refs covers both the unresolved-lookup-ref and non-unique-attr error paths). dune build impl/ green.

docs/upstream_differences.md updated: the "Direct Lookup Refs Scan Visible Datoms" divergence is now resolved.

Link to Devin session: https://app.devin.ai/sessions/7705343425064c3a9b38d8b0e4ceb045
Open in Devin Desktop: https://app.devin.ai/desktop/session/7705343425064c3a9b38d8b0e4ceb045?variant=devin
Requested by: @tiensonqin

[devin-ai-integration]

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