fix: keep vector fields in from_existing on RESP2 unified FT.INFO replies

[desty]

Fixes #712

Problem

With redis-py 8 on a RESP2 connection created with legacy_responses=False, FT.INFO puts vector params into the field's flags list:

{'identifier': 'h', 'attribute': 'h', 'type': 'VECTOR',
 'flags': ['algorithm', 'HNSW', 'data_type', 'FLOAT32', 'dim', 8,
           'distance_metric', 'L2', 'M', 24, 'ef_construction', 300, 'INDEXMISSING']}

The dict branch of parse_vector_attrs skipped flags entirely. It found no dims and returned None, and convert_index_info_to_schema then dropped the field with a bare continue. As a result, SearchIndex.from_existing() + create() silently rebuilt the index without its vector fields.

Changes

1. The dict branch of parse_vector_attrs now unpacks key/value pairs from flags. It skips valueless modifiers such as INDEXMISSING; I checked on Redis 8.4 that INDEXMISSING is appended as a bare token after the pairs. Top-level keys still take precedence, so RESP3 replies (params at top level, empty flags) behave as before.
2. When a vector field is skipped, a warning now names the field and the index, so the skip is no longer silent.

Testing

• Reproduced against redis:8.4 + redis-py 8.1.0 with a FLAT and an HNSW (m=24, ef_construction=300) vector field. Before this change, from_existing returned ['cat', 'text'] for protocol=2, legacy_responses=False. After it, all three client configurations (protocol=2, protocol=2, legacy_responses=False, protocol=3) recover the identical schema, including the HNSW params.
• New unit tests in tests/unit/test_convert_index_info.py: flags unpacking with a trailing INDEXMISSING, and the skip warning. Both fail on main and pass here.
• make format and make check-types pass. Running tests/unit (excluding test_mcp) plus tests/integration/test_connection.py gives the same result as on main: the pre-existing test_repr failures and google_genai optional-dependency errors, which are unrelated to this change, plus the 2 new tests passing.

AI disclosure: this change was prepared with an AI coding assistant (Claude Code). I reviewed the diff and ran the tests above.

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes index schema reconstruction from FT.INFO for vector fields; incorrect parsing could still misrepresent indexes on recreate, but scope is limited to a known redis-py 8 RESP2 reply shape.

Overview
Fixes silent loss of vector fields when rebuilding schemas from FT.INFO under redis-py 8 on RESP2 with legacy_responses=False, where vector parameters are encoded as key/value pairs inside the field's flags list (sometimes followed by bare modifiers like INDEXMISSING).

parse_vector_attrs now walks those flags pairs when attributes arrive as a dict, skipping valueless FT.INFO modifiers via _VECTOR_VALUELESS_FLAGS, while still preferring top-level keys so RESP3-style replies are unchanged. When vector attributes still cannot be parsed, convert_index_info_to_schema logs a warning naming the field and index instead of dropping the field quietly—restoring correct behavior for SearchIndex.from_existing() / index recreation.

Unit tests cover RESP2 unified flags unpacking (including HNSW params and trailing INDEXMISSING) and the new skip warning.

^{Reviewed by Cursor Bugbot for commit 192d689. Bugbot is set up for automated code reviews on this repo. Configure here.}