fix: remove .expect() calls in FailoverProvider::try_providers

[ztsalexey]

Summary

• Replace .expect("providers list is non-empty") with .ok_or_else()? error propagation
• Replace .expect("available providers list is non-empty") with .unwrap_or_else() fallback error

Both were logically unreachable but violated the project no-panic convention.

Closes #155

Test plan

• All 17 existing failover tests pass: cargo test --lib llm::failover
• No behavioral change — both paths were unreachable; only the panic-on-invariant-violation behavior changes to error propagation

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @ztsalexey, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors error handling within the FailoverProvider to eliminate potential panics from .expect() calls. By replacing these with more robust error propagation and fallback mechanisms, the codebase now aligns better with a no-panic convention, enhancing stability and predictability without altering the intended logic or behavior of the failover system.

Highlights

• Panic Prevention: Replaced .expect() calls with explicit error propagation (.ok_or_else()?) and fallback (.unwrap_or_else()) to adhere to the project's no-panic convention.
• Error Handling Improvement: Introduced LlmError::RequestFailed with specific reasons for cases where provider lists are unexpectedly empty or all providers fail, improving error clarity.
• Behavioral Consistency: Confirmed that these changes introduce no behavioral differences, as the original .expect() paths were logically unreachable.

Changelog

• src/llm/failover.rs
  • Replaced .expect("providers list is non-empty") with an ok_or_else call that returns LlmError::RequestFailed if no providers are available.
  • Replaced .expect("available providers list is non-empty") with an unwrap_or_else call that returns LlmError::RequestFailed if all providers fail.

Activity

• All 17 existing failover tests passed, confirming no regressions.
• No behavioral changes were introduced, as the modified code paths were previously unreachable.
• The pull request was generated using Claude Code.

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[Copilot]

Pull request overview

This PR removes two .expect() calls from the FailoverProvider::try_providers method to comply with the project convention of never using .unwrap() or .expect() in production code. Both calls were logically unreachable due to constructor invariants, but could have caused panics if future refactoring violated those invariants.

Changes:

• Replaced .expect("providers list is non-empty") with .ok_or_else()? for proper error propagation when selecting the oldest-cooled provider
• Replaced .expect("available providers list is non-empty") with .unwrap_or_else() to provide a fallback error when all providers fail

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[gemini-code-assist]

Code Review

This pull request correctly replaces .expect() calls with non-panicking error handling, which improves the robustness of the FailoverProvider and aligns with a no-panic policy. The changes are well-reasoned and improve the code quality. I have one minor suggestion to improve the clarity of an error message in a theoretically unreachable code path, which could aid debugging if a bug ever makes that path reachable.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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