Cache persistence: persist bq_memory_limited flag in QueryCacheManager
so truncation warnings survive cache hits. The flag is now saved into
the cache value dict in set_query_result (reading from g and resetting
it there), and restored from cache in get(). get_df_payload now reads
cache.bq_memory_limited instead of g, removing the need for g entirely
in query_context_processor.py.
Frontend test: add two tests to chartActions.test.ts verifying that
addWarningToast is dispatched (with noDuplicate: true) when a query
response carries a warning field, and not dispatched when it doesn't.
Updated existing test_query_context_processor tests to set the flag on
mock_cache directly rather than patching g.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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