[Anish Mehta (anishmehta24)]

Motivation & Context

ChatOptions.stop is typed str | Sequence[str], but four providers pass a single string straight into a field that only takes a list:

• Gemini: stop_sequences fails GenerateContentConfig validation ("Input should be a valid list").
• Bedrock: botocore rejects inferenceConfig.stopSequences ("valid types: list, tuple").
• Anthropic: the request carries stop_sequences: "END"; the API expects an array.
• Ollama: the request carries options.stop: "END"; Ollama expects a list.

OpenAI and Mistral accept a string, so they're unchanged.

Description & Review Guide

• What are the major changes? Where each of the four clients maps stop to its provider field, a plain string is wrapped in a one-item list. Lists are passed as before.
• What is the impact of these changes? options={"stop": "END"} works on these providers instead of failing or sending the wrong type.
• What do you want reviewers to focus on? I kept it in one PR since it's the same two-line change in each client; happy to split per package if you prefer.

Related Issue

No existing issue.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible

One test per provider for a single stop string (all four fail on main). The gemini, bedrock, anthropic and ollama test suites pass, and the repo's pre-commit checks are clean.

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