docs+test: soften module docstring; add fixture-scope sanity assert (#105 PR 2a)

Two small cleanups; no behavior change.

(1) src/bigquery_agent_analytics/binding_validation.py: module
docstring previously read like a PR-review note (told callers not
to import a graph_validation module that does not exist yet).
Replaced with a public-doc-shaped sentence that just describes the
relationship to #76's planned extracted-graph validator.

(2) tests/test_integration_ontology_binding.py: the live test
TestBindingValidationLive depends on two function-scope fixtures
(isolated_scratch and isolated_ontology_and_binding), and the
second's binding YAML embeds the first's dataset id. If either
fixture is later flipped to module scope by accident, the binding
would point at a stale dataset. New assertion
binding.target.dataset == ds_id catches that drift before any BQ
call runs.

Live test still PASSES against test-project-0728-467323 (13.24s).

Author: caohy1988

src/bigquery_agent_analytics/binding_validation.py

@@ -20,12 +20,9 @@
 most common authoring error (binding YAML drifted out of sync with
 physical tables) before extraction wastes ``AI.GENERATE`` tokens.
 
-Different from the planned extracted-graph validator in issue #76:
-that one will validate extracted graph output against the spec
-(post-extraction, pre-materialization). This one validates the
-binding against the live BigQuery schemas (pre-extraction). #76 has
-not landed yet, so do not import any symbol from a
-``graph_validation`` module — it does not exist on this PR.
+Different from the planned extracted-graph validator in #76, which
+will validate ``ExtractedGraph`` output against the resolved spec
+after extraction. This validator runs before extraction.
 
 Usage::
 

tests/test_integration_ontology_binding.py

@@ -748,6 +748,18 @@ def test_validator_end_to_end_against_real_bigquery(
     client, ds_id = isolated_scratch
     ontology, binding = isolated_ontology_and_binding
 
+    # Cheap fixture-scope sanity check: the binding YAML the second
+    # fixture wrote must point at the dataset the first fixture
+    # created. If a future refactor flips either fixture to module
+    # scope by accident, the binding would race with whichever
+    # dataset was created first and this assert would catch it
+    # before any BQ call runs.
+    assert binding.target.dataset == ds_id, (
+        f"binding.target.dataset={binding.target.dataset!r} but "
+        f"isolated_scratch yielded {ds_id!r}; fixture scopes are "
+        f"out of sync"
+    )
+
     # Phase 1: materialize real tables.
     mat = OntologyMaterializer.from_ontology_binding(
         ontology=ontology,