fix(responses): report truncation and normalize the translated output shape

[SantiagoDePolonia]

Three /v1/responses output-shape gaps, all visible on translated (non-native-OpenAI) providers.

Truncation is reported. A turn stopped by max_output_tokens (or a content filter) now returns status: "incomplete" with incomplete_details.reason, and the message item carries status: "incomplete" — chat-translated providers (gemini, groq, deepseek, …) and Anthropic, in both stream and non-stream. core.ResponsesResponse gained the typed incomplete_details field, so native OpenAI's value is no longer dropped either (it previously returned status: "incomplete" with no details).

Empty answers keep text. output_text parts always serialize text, which the OpenAI schema requires; an empty assistant answer used to emit {"type":"output_text","annotations":[]}. The streamed path already did this.

Usage is normalized. The Responses usage object now carries only the OpenAI shape (input_tokens/output_tokens/total_tokens plus *_tokens_details), instead of leaking provider members such as thoughts_token_count, completion_reasoning_tokens or completion_time. Nothing with an OpenAI-shaped home is lost: reasoning tokens stay under output_tokens_details, cached tokens under input_tokens_details (Anthropic's Responses usage now fills both). Provider extras remain in RawUsage, which feeds usage records and cost calculation, and the Anthropic streamed usage payload keeps its cache counts because stream costs are read back from it.

Provider notes: gemini 2.5 flash can return a completely empty stream (no chunk, no finish_reason, no usage) when the whole budget goes to thinking — nothing to map there; that stream still ends completed.

Tested: unit tests for each path (internal/core, internal/providers, internal/providers/anthropic), go test ./... (pre-existing failures only: dashboard assets, a midnight-boundary version-cookie test), make lint clean, API docs regenerated. Live gateway run against anthropic/gemini/groq/openai with max_output_tokens=16, stream and non-stream: all four now report incomplete + max_output_tokens, usage normalized, empty answer serializes "text": "".

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📥 Commits

Reviewing files that changed from the base of the PR and between 1d4ae81 and c5b7a60.

📒 Files selected for processing (17)

• cmd/gomodel/docs/docs.go
• docs/openapi.json
• internal/core/responses.go
• internal/core/responses_incomplete_test.go
• internal/core/responses_json.go
• internal/core/usage_json.go
• internal/core/usage_json_test.go
• internal/providers/anthropic/responses.go
• internal/providers/anthropic/responses_status_test.go
• internal/providers/responses_converter.go
• internal/providers/responses_output.go
• internal/providers/responses_status_test.go
• internal/providers/responses_stream_status_test.go
• internal/usage/cached_responses_test.go
• internal/usage/cost.go
• tests/contract/testdata/golden/groq/responses.golden.json
• tests/contract/testdata/golden/xai/responses.golden.json

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Codecov Report

❌ Patch coverage is 96.29630% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/providers/responses_converter.go	90.90%	1 Missing ⚠️
internal/providers/responses_output.go	94.44%	1 Missing ⚠️

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[greptile-apps]

Confidence Score: 5/5

Safe to merge.

_{Reviews (2) · Last reviewed commit: "fix(usage): price Anthropic cache reads ..."}