Python: Bug: Redis connector sends malformed FT.CREATE PREFIX (one prefix per character of collection name) #13894

Describe the bug
The Python Redis connector sends FT.CREATE with the PREFIX argument split into one prefix per character of the collection name, instead of one prefix equal to "<collection_name>:".

Example observed on the wire for a collection named redis_json_list_data_model:

FT.CREATE redis_json_list_data_model ON JSON
  PREFIX 27 r e d i s _ j s o n _ l i s t _ d a t a _ m o d e l :
  SCORE 1.0 SCHEMA ...

RediSearch on Redis Stack silently accepts the malformed command and the connector appears to work for simple single-collection usage.

Root cause (client-side): python/semantic_kernel/connectors/redis.py:281 passes a plain string to redis-py's IndexDefinition(prefix=...). redis-py treats that argument as an iterable of prefixes and iterates the string character-by-character.

Expected behavior

FT.CREATE for an SK-managed collection should register exactly one key-space prefix equal to "<collection_name>:", so that the index only matches keys written for this collection.

FT.CREATE redis_json_list_data_model ON JSON
  PREFIX 1 redis_json_list_data_model:
  SCORE 1.0 SCHEMA ...

To Reproduce

Prerequisites: a Redis Stack server reachable on localhost:6379, redis-cli, and a working Python SK dev environment.

1. Install Python SK per (python/DEV_SETUP.md):

   cd python && make install-sk PYTHON_VERSION=3.12

2. Start Redis Stack on port 6379. Example:

   podman run -d -p 6379:6379 docker.io/redis/redis-stack:latest

3. In a separate terminal, attach MONITOR to the server:

   redis-cli -h localhost -p 6379 MONITOR

4. From python/, run the Redis integration tests:

   REDIS_CONNECTION_STRING="redis://localhost:6379" \
     uv run pytest tests/integration/memory/test_vector_store.py -k redis -v

5. Inspect the MONITOR output for the FT.CREATE lines. Each one contains PREFIX <N> where N equals the length of the collection name, followed by that many single-character prefixes.

On Redis Stack the tests pass (the bug is silent).

Platform

• Language: Python
• Source: main branch of microsoft/semantic-kernel (SK version 1.41.2 as reported by semantic_kernel.__version__)
• redis-py version: 6.4.0
• Backends tested:
  • Redis Stack 7.4.7 (RediSearch v21020, ReJSON v20809) — bug is silent, FT.CREATE accepted
• AI model: [e.g. OpenAI:GPT-4o-mini(2024-07-18)]
• IDE: Kiro
• OS: macOS 25.4.0 (Darwin), arm64

Additional context

Correctness on Redis: indexes register unintended single-character prefixes. In multi-collection deployments on a shared Redis, collections whose names share any character will register overlapping prefixes and can match each other's keys.