US-009: Add comprehensive unit tests for kimi model compatibility fix

Added 4 unit tests to verify is_error field handling for kimi models:
- model_rejects_is_error_field_detects_kimi_models: Detects kimi-k2.5, kimi-k1.5, dashscope/kimi-k2.5 (case insensitive)
- translate_message_includes_is_error_for_non_kimi_models: Verifies gpt-4o, grok-3, claude include is_error
- translate_message_excludes_is_error_for_kimi_models: Verifies kimi models exclude is_error (prevents 400 Bad Request)
- build_chat_completion_request_kimi_vs_non_kimi_tool_results: Full integration test for request building

All 119 unit tests and 29 integration tests pass.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

progress.txt

@@ -81,3 +81,16 @@ VERIFICATION STATUS:
 - cargo clippy --workspace: PASSED
 
 All 7 stories from prd.json now have passes: true
+
+Iteration 2: 2026-04-16
+------------------------
+
+US-009 COMPLETED (Add unit tests for kimi model compatibility fix)
+- Files: rust/crates/api/src/providers/openai_compat.rs
+- Added 4 comprehensive unit tests:
+  1. model_rejects_is_error_field_detects_kimi_models - verifies detection of kimi-k2.5, kimi-k1.5, dashscope/kimi-k2.5, case insensitivity
+  2. translate_message_includes_is_error_for_non_kimi_models - verifies gpt-4o, grok-3, claude include is_error
+  3. translate_message_excludes_is_error_for_kimi_models - verifies kimi models exclude is_error (prevents 400 Bad Request)
+  4. build_chat_completion_request_kimi_vs_non_kimi_tool_results - full integration test for request building
+- Tests: 4 new tests, 119 unit tests total in api crate (+4), all passing
+- Integration tests: 29 passing (no regressions)