feat(ai): preserve streamed refusals as text - #43343

…ncode#43343)

A model that declines mid-stream delivers the explanation on the
structured refusal channel (chat_completions delta.refusal; Responses
response.refusal.delta / refusal content parts) and leaves content
empty. The streaming accumulators dropped that channel entirely, so a
streamed refusal assembled into an empty message and fell into the
empty/invalid-response retry loops - burning paid retries reproducing a
deterministic refusal - while the non-streaming path had already fixed
this class in #46013.

- chat_completions streaming: accumulate delta.refusal (incl.
  model_extra), expose message.refusal on the assembled mock response so
  ChatCompletionsTransport.normalize_response applies the existing
  sole-payload -> content_filter promotion; count refusal deltas in the
  zero-chunk guard; carry refusal in the Relay final-response dict.
- Codex Responses stream consumer: collect response.refusal.delta as
  answer text so a refusal-only stream no longer raises 'did not emit a
  terminal response' with zero usable content.
- Responses normalizer: read type=refusal content parts in
  _extract_responses_message_text (attr and dict shapes).

Sabotage-verified: each new test fails with its wiring line disabled.
E2E: refusal-only stream -> terminal content_filter with explanation;
refusal-alongside-content stays a normal usable turn; plain-text
streams unchanged.

…ncode#43343)

A model that declines mid-stream delivers the explanation on the
structured refusal channel (chat_completions delta.refusal; Responses
response.refusal.delta / refusal content parts) and leaves content
empty. The streaming accumulators dropped that channel entirely, so a
streamed refusal assembled into an empty message and fell into the
empty/invalid-response retry loops - burning paid retries reproducing a
deterministic refusal - while the non-streaming path had already fixed
this class in #46013.

- chat_completions streaming: accumulate delta.refusal (incl.
  model_extra), expose message.refusal on the assembled mock response so
  ChatCompletionsTransport.normalize_response applies the existing
  sole-payload -> content_filter promotion; count refusal deltas in the
  zero-chunk guard; carry refusal in the Relay final-response dict.
- Codex Responses stream consumer: collect response.refusal.delta as
  answer text so a refusal-only stream no longer raises 'did not emit a
  terminal response' with zero usable content.
- Responses normalizer: read type=refusal content parts in
  _extract_responses_message_text (attr and dict shapes).

Sabotage-verified: each new test fails with its wiring line disabled.
E2E: refusal-only stream -> terminal content_filter with explanation;
refusal-alongside-content stays a normal usable turn; plain-text
streams unchanged.

…t (port of anomalyco/opencode#43343)

…ncode#43343)

…ncode#43343)

…ncode#43343)