Language model providers can reject a request inside an otherwise
successful response stream. Those failures were represented by
overlapping completion-error variants and provider-specific code enums,
and OpenAI Responses errors such as `cyber_policy` fell through to
`Other`. Agent sessions consequently retried permanent provider
rejections and user interfaces lost the provider's actionable message.

This gives every provider-originated failure one shared representation.
`ProviderRejection` preserves the provider, exact message, retry delay,
raw provider code, and an HTTP status only when one was actually
reported. `ProviderErrorCategory` supplies the normalized meaning used
by shared UI and policy code. Provider adapters map their native wire
errors into that category explicitly, so typed SDK exceptions and errors
embedded in successful streams no longer fabricate HTTP statuses.

Retry selection is independent from error construction.
`LanguageModelCompletionError::retry_delay` owns transient
classification and a bounded schedule of 5, 10, 20, then 40 seconds. A
provider-supplied `retry_after` overrides that schedule. The scheduling
layer adds positive jitter of up to 10%, while interactive requests and
evaluation runs retain their own attempt budgets. Permanent status-less
errors such as `cyber_policy` do not retry. OpenRouter also keeps its
numeric body code distinct from an optional HTTP status, including for
errors embedded in a stream.

Testing performed:

- `corgi test -p language_model_core`
- `corgi test -p anthropic` (33 tests)
- `corgi test -p open_ai` (77 tests)
- `cargo nextest run -p open_router -p copilot_chat -p
language_models_cloud -p language_models` (125 tests)
- `cargo nextest run -p agent -p agent_ui` (1,153 tests; 11 skipped)
- `cargo check -p open_router -p copilot_chat -p language_models_cloud
-p language_models -p agent -p agent_ui`
- `./script/clippy -p language_model_core -p anthropic -p open_ai -p
open_router -p copilot_chat -p language_models_cloud -p language_models
-p agent -p agent_ui` completed the release Clippy phase; Cargo Shear
then reported the repository's existing warnings
- `cargo fmt --all --check`

Suggested .rules additions

None.

Release Notes:

- Fixed permanent language model provider rejections being retried and
displayed without their actionable provider message.