add support for LiteLLM

[senko]

This will become the default backend in the future (replacing inhouse backends), so it's immediately required as a non-optional dep.

[greptile-apps]

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[Copilot]

Pull Request Overview

This PR adds support for LiteLLM as a new backend provider, which will replace in-house backends in the future. LiteLLM provides a unified interface to 100+ LLM providers through an OpenAI-compatible API format.

• Implements LiteLLMAdapter to convert between think's internal format and OpenAI-compatible format
• Adds LiteLLMClient as the main entry point for LiteLLM functionality
• Integrates LiteLLM into the existing provider system with registration and configuration

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
think/llm/litellm.py	Complete implementation of LiteLLM adapter and client classes
think/llm/base.py	Adds "litellm" to providers list and registers LiteLLMClient
tests/llm/test_litellm_adapter.py	Comprehensive test suite for the LiteLLM adapter functionality
tests/conftest.py	Adds LiteLLM model URL to test configuration when OpenAI API key is available
pyproject.toml	Adds litellm>=1.75.7 as a required dependency

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[Copilot]

The ValueError constructor is being called with two arguments, but the second argument tc is not formatted into the string. This should use string formatting like f"Missing tool call ID in assistant message: {tc!r}" or use a single string argument.

Suggested change

	"Missing function arguments in assistant message: %r", tc
	f"Missing tool call ID in assistant message: {tc!r}"
	)
	name = tc.get("function", {}).get("name")
	if name is None:
	raise ValueError(
	f"Missing function name in assistant message: {tc!r}"
	)
	arguments = tc.get("function", {}).get("arguments")
	if arguments is None:
	raise ValueError(
	f"Missing function arguments in assistant message: {tc!r}"

[Copilot]

The ValueError constructor is being called with two arguments, but the second argument tc is not formatted into the string. This should use string formatting like f"Missing function name in assistant message: {tc!r}" or use a single string argument.

Suggested change

	"Missing function name in assistant message: %r", tc
	f"Missing function name in assistant message: {tc!r}"

[Copilot]

The ValueError constructor is being called with two arguments, but the second argument tc is not formatted into the string. This should use string formatting like f"Missing function arguments in assistant message: {tc!r}" or use a single string argument.

Suggested change

	"Missing function arguments in assistant message: %r", tc
	f"Missing function arguments in assistant message: {tc!r}"

[Copilot]

The ValueError constructor is being called with two arguments, but the second argument message is not formatted into the string. This should use string formatting like f"Missing content in user message: {message!r}" or use a single string argument.

Suggested change

	raise ValueError("Missing content in user message: %r", message)
	raise ValueError(f"Missing content in user message: {message!r}")

[Copilot]

The expression text or "" is redundant since text is already guaranteed to be non-None and non-empty due to the if text: condition on line 220. The fallback to empty string is unnecessary here.

Suggested change

	text=text or "",
	text=text,