Fix tests and GitHub Actions failures - clippy warnings, formatting, and key rotation logic

[Copilot]

Overview

This PR fixes all failing tests and GitHub Actions CI checks in the repository. The issue was caused by three categories of problems: code quality violations (clippy warnings), code formatting inconsistencies, and actual bugs in integration tests.

Issues Fixed

1. Code Quality & Formatting

Fixed multiple clippy warnings that were blocking CI with -D warnings:

• Replaced manual Default implementation with #[derive(Default)] for Config struct
• Removed useless type conversions (e.g., reqwest::Error::from())
• Updated to use modern std::io::Error::other() API
• Simplified duplicate conditional branches
• Added #[allow(dead_code)] for public API functions and removed unused test helpers
• Cleaned up unused imports across test files and benchmarks
• Fixed async benchmark syntax to use iter_custom instead of deprecated to_async

Applied cargo fmt across all 17 modified files to ensure consistent formatting.

2. Key Rotation Logic Bug

Problem: The test_api_key_rotation_on_rate_limit test was failing because the proxy wasn't actually rotating to different API keys when retrying after rate limit errors.

Root Cause: When the first key returned a 429 (rate limited) response, the retry loop would call get_key_for_model() again, which always returned the same key because it was the best match for the requested model (e.g., "gpt-3.5-turbo").

Solution: Modified the ProxyEngine to track retry state and switch to using get_next_key() after the first failure, ensuring actual key rotation through all available keys:

// Before: Always used get_key_for_model() - would return same key
let key_info = self.key_pool.get_key_for_model(&model)?;

// After: Uses get_next_key() for retries to try different keys
let key_info = if use_next_key {
    self.key_pool.get_next_key()?
} else {
    self.key_pool.get_key_for_model(&model)?
};

This ensures the proxy properly implements failover by trying different API keys when one becomes rate limited.

3. Wiremock Test Configuration

Problem: The test_api_streaming_response test was failing because the content-type header wasn't being preserved in the response.

Root Cause: Wiremock's set_body_string() method automatically sets content-type: text/plain and overrides any custom headers set with insert_header() or append_header().

Solution: Changed to use set_body_bytes() which doesn't override custom headers:

// Before: set_body_string() overwrote custom content-type
.set_body_string("data: ...")
.append_header("content-type", "text/event-stream")

// After: set_body_bytes() preserves custom headers
.set_body_bytes("data: ...")
.append_header("content-type", "text/event-stream")

Additional Fix: Added proper mock setup for the test_api_error_handling_no_available_keys test to handle the "others" fallback key scenario.

Test Results

All test suites now pass:

• ✅ Unit Tests: 9/9 passed
• ✅ Enhanced Unit Tests: 18/18 passed
• ✅ Integration Tests: 9/9 passed (was 6/9)
• ✅ Performance Tests: 5/5 passed
• ✅ Code Formatting: cargo fmt --check passes
• ✅ Clippy: cargo clippy -- -D warnings passes

Impact

• Improved Reliability: Key rotation now works correctly, providing better fault tolerance when upstream APIs rate limit
• CI/CD Ready: All GitHub Actions checks will now pass
• Code Quality: Codebase now meets Rust best practices with zero warnings
• Test Coverage: All 41 tests pass reliably

The changes are minimal and surgical, focusing only on fixing identified issues without modifying working code.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• definitely-not-a-real-domain-12345.com
  • Triggering command: /home/REDACTED/work/key-cycle-proxy/key-cycle-proxy/target/debug/deps/enhanced_unit_tests-1efd28ab9ffdee84 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>fix: tests and actions bugs</issue_title>
<issue_description>tests and github actions are all failing</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #16

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