Profile-level reasoning_enabled was attached as an instance attribute
after construction only when a profile matched; the base class never
declared it and consumers probed with double getattr. Any code that
accidentally set client.reasoning_enabled would silently override the
global switch.
The flag is now an explicit LLMClient constructor parameter with
three-state semantics: True/False (profile-level explicit, or the
global api.reasoning_enabled value concretized when the profile omits
the field) and None (no profile -> consumer falls back to global).
create_llm_client passes it at construction and no longer mutates the
client afterwards; DeepSeekChat._reasoning_enabled simplifies to a
single getattr probe that still tolerates clients without the attr.
Tests: TestM3ReasoningConstructor (4 cases) covering profile True,
profile-omitted -> global concretized, base default None, and the
None -> global fallback at the consumer; one legacy assertion updated
to the new contract (attribute exists, value None). Full suite 299
passed.
qing
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