Summary

Closes the chained-reentry portion of slice 4.3d (#1256) so multi-alias whole-row carry survives more than one reentry boundary. Builds on top of #1248 / #1071 which together enabled single-boundary multi-alias carry.

Closes (partial) #1256 — chained-reentry portion. The free-form intermediate-MATCH case (LDBC SNB IC3 prefix shape, where the trailing MATCH does not start from any carried alias) remains open follow-up.

Before / after

Before (against master 80d80849c):

MATCH (a:A {id: 'a'}), (x:B {id: 'b'})
WITH a, x
MATCH (a)-[:R]->(friend)
WITH friend, x
MATCH (friend)-[:S]->(c)
RETURN c.id, x.id
-- GFQLValidationError: Unknown Cypher alias '__cypher_reentry_x_id__' in RETURN clause

After: returns the expected rows; the secondary alias x's hidden carry column survives the reentry-source rebinding.

What changed

graphistry/compute/gfql/cypher/lowering.py — two extensions to _demote_secondary_whole_row_aliases (the active rewrite path on master after #1071 superseded slice 4.3b's _rewrite_multi_whole_row_prefix):

1. Forwarding-item drop — bare-identifier projection items in downstream WITH stages whose name is a secondary alias are dropped at compile time before _collect_secondary_property_refs walks them for bare references. Same intent as slice 4.3c, integrated into the active path. Without this, forwarding patterns like WITH a, x, friend, ... tripped the bare-ref failfast even though the property carry already lives as a hidden scalar on the reentry-source's row table.

2. Hidden-column forwarding — for every (secondary_alias, prop) collected from trailing clauses, the synthesized __cypher_reentry_<S>_<X>__ hidden alias is appended as a bare passthrough item to every downstream WITH stage so each recursive compile_cypher_query call sees it as a scalar carry. Without this, the inner compile failed alias resolution on the rewritten hidden identifier once a chained stage narrowed the projection scope.

Tests

graphistry/tests/compute/gfql/cypher/test_lowering.py:

• test_string_cypher_admits_multi_stage_secondary_alias_carry_through_chained_reentry — chained reentry where the trailing MATCH continues to use the same primary alias (a → friend → other, both reentry MATCHes rooted at a).
• test_string_cypher_admits_secondary_alias_carry_across_reentry_source_rebinding — source rebound between boundaries (MATCH (a)-[:R]->(friend) ... MATCH (friend)-[:S]->(c)); x.id carries through.
• test_string_cypher_admits_multi_alias_distinct_forwarding_through_reentry — multi-alias WITH DISTINCT forwarding through a single boundary.
• test_string_cypher_failfast_rejects_intermediate_reentry_match_with_no_carried_source — pins the remaining gap (free-form intermediate MATCH that does not start from any carried alias) to the existing scoped error so future closure is regression-locked.

Existing slice 4.1 / 4.3a / 4.3b / 4.3c tests stay green (regression net).

Validation

• pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py — 780 passed, 67 skipped (was 776 before; +4 new tests). No regressions.
• ./bin/ruff.sh clean.
• ./bin/mypy.sh on lowering.py clean. (Pre-existing mypy errors in test_lowering.py are unrelated; verified present on master.)
• Repro plans/1256-cross-reentry-boundary-carry/repro/repro_ic3.py: simple rebinding cases now compile + execute correctly. The literal IC3 query still fails at the free-form intermediate MATCH gate (MATCH (city:City)-[:IS_PART_OF]->(country:Country) — neither alias is carried) — separate follow-up tracked under Cypher/GFQL: forward bounded-reentry carry hidden columns across reentry-source rebinding (LDBC SNB IC3) #1256.
• cuDF lane: not yet run (no _cudf variant of new tests in this PR — pure compile-time change uses existing scalar-carry runtime plumbing that already has cuDF coverage; will spot-check on DGX before merge).

Test plan

• pytest -q graphistry/tests/compute/gfql/cypher/
• ./bin/ruff.sh
• ./bin/mypy.sh on touched files
• Hosted CI green (push pending)
• cuDF spot-check on DGX
• Review skill converged

Refs

• Closes (partial) Cypher/GFQL: forward bounded-reentry carry hidden columns across reentry-source rebinding (LDBC SNB IC3) #1256 — chained-reentry portion; free-form intermediate MATCH remains open
• Refs Cypher/GFQL rejects multi-stage MATCH ... WITH ... MATCH ... WITH ... MATCH read queries #999 (IC3 lane partial)
• Refs Cypher/GFQL: introduce a first-class row-carrier IR for multi-stage vectorized row semantics #989 (row-carrier IR umbrella)
• Predecessor: feat(cypher): ReentryPlan + multi-whole-row prefix WITH (#989 slices 4.1+4.3a) #1248 (slices 4.1 / 4.3a / 4.3b / 4.3c, master 80d80849c)
• Plan: plans/1256-cross-reentry-boundary-carry/plan.md

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