Stacked on #27703.
Provider option conversion, reasoning effort injection, and file part
acceptance each recomputed the OpenAI wire format from `(provider,
modelID, override)`. They now read it from `chatprovider.Model`, so a
decision cannot drift from the client it was built for.
`ProviderOptionsFromChatConfig` takes a `Transport`,
`ApplyReasoningEffort` takes a `Model`, and `AcceptsFilePartMediaType`
becomes a `Model` method. `UsesResponsesAPI` and `UsesResponsesOptions`
are deleted. The override extraction is unexported and reachable only
from `ModelFromConfig`, which now takes the model's
`ChatModelOpenAIConfig` directly, removing the six scattered extractions
at call sites.
That also resolves the computer-use mismatch. The computer-use model is
a hardcoded default with no config row of its own: its client was built
without an override while request preparation applied the chat model's.
Preparation now reads the computer-use model's own transport, so the two
agree without one model's client settings following a different model.
Passing the chat model's `openai_config` into the computer-use client
would have made them agree on the wrong value.
`TestModelTransportConsumersAgree` pins the invariant in one test: the
HTTP path the client actually hits, the concrete provider option struct
type, the type created by reasoning effort, and text/image file
acceptance.
> Mux prepared this PR on Mike's behalf.
Stacked on #27683.
The OpenAI wire format is decided when the client is built, then thrown
away, so downstream sites recompute it from `(provider, modelID,
override)`. Any disagreement fails silently: the SDK type-asserts the
concrete provider options struct and discards every OpenAI option, and
text attachments are dropped because Responses natively accepts only
images and PDFs.
This adds `chatprovider.Model`, which pairs a fantasy client with the
transport resolved from that client's own identity. Its fields are
unexported and only the constructor sets the transport, deriving it from
the client, so no caller can pick a transport that disagrees with the
client it wraps. `chatopenai.Transport`'s zero value is invalid and
panics when read rather than defaulting to a wire format, following the
existing precedent for construction invariants.
`Model` is threaded through construction, the resolve paths, and the
four struct fields that store a model for later request preparation.
Terminal call sites keep taking `fantasy.LanguageModel` and receive
`LanguageModel()`, which avoids a new package edge from `chatloop` and
`chatadvisor` into `chatprovider`.
No decisions move yet. The consumers still recompute the transport, and
`UsesResponsesAPI` now delegates to `TransportFor` so the two agree by
construction. #27704 makes the consumers read it from the model.
> Mux prepared this PR on Mike's behalf.
Michael Suchacz