Test: cover enable_thinking precedence (top-level > kwarg > --thinking) at handler level #263

Follow-up from the review of #260 (merged as 7376b6b), which fixed #259.

Gap. The precedence in handleChatCompletion (top-level enable_thinking, then chat_template_kwargs.enable_thinking, then --thinking) is inline in the handler. chatTemplateContext takes the already-decided Bool, so the four new unit tests in tests/SwiftLMTests/ChatRequestParsingTests.swift never see the precedence. tests/test-contract.sh test 17 only checks that mixed-type kwargs are accepted, and 17b checks the 400 body. Swapping the precedence branches leaves every test green.

Suggested test. Move the precedence decision into a small pure function (for example resolveThinking(topLevel:kwarg:config:)) and test each branch, including the conflicting case where the top-level value must win over the kwarg. Add one contract case with a top-level value that conflicts with the kwarg.

Severity: medium (no current bug; a regression guard).