conformance: EXISTS existentialsubquery TCK scenarios green (tck-gfql#193)

CHANGELOG.md

@@ -57,6 +57,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - **dgx GB10 benchmark safety harness**: `benchmarks/dgx/{safe_run.sh, preflight.py, sitecustomize.py, local_run.sh}` — an RMM device-allocation cap + host-memory watchdog + preflight refusal + hard timeout for running GPU / large-graph benchmarks on the unified-memory GB10 box without OOM-wedging it. Developer/benchmark tooling only; no runtime or library behavior change.
 - **Docs CI: polars in the doc-test image (pinned)**: the Sphinx doc-example runner now installs `polars` (pinned to cooldown-safe versions) so `engine='polars'` documentation examples execute — and are SKIPPED, not failed, where polars is unavailable (e.g. the minimal-deps job, Python 3.14). Doc-build / CI only; no runtime or library change.
+- **openCypher TCK conformance: `EXISTS { }` existential-subquery scenarios (`expr-existentialsubquery1-1`, `1-3`) now pass**, unblocking the `tck-gfql` CI job. No pygraphistry code change — pygraphistry already renders these correctly (a whole-entity `RETURN n` over a simple-pattern `EXISTS { }` yields the expected entity-text rows). The `success_wrong_rows` was purely a property-map display-whitespace convention (`(:A {prop: 1})` vs the TCK oracle's `(:A {prop:1})`; both valid Cypher). Reconciled harness-side in [tck-gfql#193](https://github.com/graphistry/tck-gfql/pull/193): entity-text whitespace normalization + promoting the two scenarios to supported (and deflaking the pre-existing scipy-`svds` `firstparty-networkx-hits-1` fixture). Conformance/CI only; no runtime or library behavior change.
 
 ## [0.57.0 - 2026-06-28]
 

graphistry/compute/gfql/cypher/result_postprocess.py

@@ -186,6 +186,12 @@ def render_entity_text(
     the Cypher display string (``(:Label {..})`` / ``[:TYPE {..}]``). Used by the
     conformance/TCK driver and by callers who want the human-readable form. The
     structured data path itself never pays this cost.
+
+    Property maps render with a space after the key colon (``(:A {prop: 1})``) —
+    our long-standing display convention. The openCypher TCK oracle omits it
+    (``(:A {prop:1})``); the whitespace is insignificant Cypher, so the TCK
+    harness normalizes it rather than us changing this convention across ~350
+    tests (see tck-gfql#193 / CHANGELOG).
     """
     rows_df = cast(DataFrameT, result._nodes)
     if rows_df is None:

graphistry/tests/compute/gfql/test_engine_polars_conformance_matrix.py

@@ -752,6 +752,39 @@ def test_exists_prune_isolated_flavors_all_engines():
         _assert_invariant(g, q, f"prune-isolated {q}")
 
 
+def test_exists_whole_entity_return_renders_entity_text():
+    """Regression for openCypher TCK expr-existentialsubquery1-1 (tck-gfql#193):
+    a WHOLE-ENTITY ``RETURN n`` over a simple-pattern ``EXISTS { }`` renders the
+    correct entity text (label + property), not leaked internal marker columns.
+    Graph mirrors the TCK fixture — node ``a`` is the only one with an out-edge —
+    so the EXISTS filter keeps exactly ``a`` and it renders ``(:A {prop: 1})``.
+
+    ``id`` is a STRING on purpose: a numeric id would render as an extra
+    property (``{id: 0, prop: 1}``). ``n.id`` is the #1650 flattened
+    whole-entity projection column, not user-aliased output."""
+    import pandas as pd
+    from graphistry.compute.gfql.cypher.result_postprocess import render_entity_text
+    nodes = pd.DataFrame({
+        "id": ["a", "b", "c", "d"],
+        "label__A": [True, False, False, False],
+        "label__B": [False, True, False, False],
+        "label__C": [False, False, True, False],
+        "label__D": [False, False, False, True],
+        "prop": [1, 1, 2, 3],
+    })
+    edges = pd.DataFrame({"s": ["a", "a", "a"], "d": ["b", "c", "d"], "eid": [0, 1, 2]})
+    g = graphistry.nodes(nodes, "id").edges(edges, "s", "d").bind(edge="eid")
+    q = "MATCH (n) WHERE EXISTS { (n)-->() } RETURN n"
+    res = g.gfql(q, engine="pandas")
+    pdf = _to_pd(res._nodes)
+    assert len(pdf) == 1, "EXISTS keeps exactly the one node with an out-edge"
+    assert pdf["n.id"].tolist() == ["a"]
+    assert render_entity_text(res, "n", table="nodes").tolist() == ["(:A {prop: 1})"]
+    # Cross-engine (this file's invariant): non-pandas engines match pandas
+    # parity or decline honestly (NIE) — whole-entity RETURN declines on polars.
+    _assert_invariant(g, q, "exists-whole-entity-return")
+
+
 def test_tolower_non_string_declines_never_fabricates():
     """toLower/toUpper on a non-string column must never return values (neo4j: type error).
     Regression (#1675 wave-1, dgx-repro'd): the scalar fallback broadcast the lowercased