fix(sse): project non-streaming JSON back to the Gemini/Antigravity envelope

[diegosouzapw]

Summary

• The streaming and non-streaming response paths disagreed on how a response is projected back into a non-OpenAI client's wire format. Streaming projects OpenAI chunks into the Gemini/Antigravity { response: { candidates: [...] } } envelope via the registered FORMATS.OPENAI -> FORMATS.ANTIGRAVITY translator; the non-streaming path only special-cased FORMATS.CLAUDE and returned the raw OpenAI chat.completion intermediate for everything else.
• Effect: a Gemini/Antigravity client on a non-streaming request received choices[]/tool_calls instead of candidates[]/functionCall. The client's parser finds no candidates and the function calls are effectively dropped — tool-calling silently breaks on the JSON path while working fine over SSE.
• Fix closes exactly that projection gap, mirroring the shape the streaming translator already emits so both paths agree.

Attribution

Thanks to @warelik for the original implementation.

Changes

• open-sse/handlers/responseTranslator.ts: add convertOpenAINonStreamingToGeminiFamily() and wire it into the Phase-3 "translate back to client format" step for FORMATS.GEMINI / FORMATS.ANTIGRAVITY.
• Tool-call arguments parse through a non-throwing helper — a provider emitting truncated JSON degrades that call's args to {} rather than raising an uncaught SyntaxError in the shared response hot path (matches the streaming translator's behaviour).
• tests/unit/nonstreaming-gemini-family-response-projection.test.ts: new regression guard (3 cases).

Scope

Deliberately narrow — only the Gemini-family projection gap proven by the failing test is closed. No refactor of the shared hot response path. Not ported from the original change: the Ollama projection (OmniRoute has no OLLAMA in FORMATS), the Responses projection, and the SSE terminal/[DONE] tracker — that handling already lives in nonStreamingSse.ts + the registry. Adjacent to #7207 (which registered an OPENAI -> GEMINI streaming projection); this covers the non-streaming path and does not overlap it.

Test plan

• targeted unit test — new, fails before / passes after:
  • before: expected {response:{candidates:[...]}} envelope for an antigravity client, got: {"id":"chatcmpl-1","object":"chat.completion","choices":[...]} (2/2 failing)
  • after: 3/3 passing
• tests/unit/plan3-p0.test.ts (pre-existing suite covering translateNonStreamingResponse) — 38/38 passing, no regression
• targeted npx tsc --noEmit on the changed file — clean (file IS in the tsconfig.typecheck-core.json allowlist)
• npx eslint on changed files — clean
• npx prettier --check on changed files — clean

[gemini-code-assist]

Code Review

This pull request implements non-streaming response translation for Gemini-family clients (Gemini and Antigravity) in open-sse/handlers/responseTranslator.ts. It introduces convertOpenAINonStreamingToGeminiFamily to project OpenAI-shaped chat completions into the expected Gemini response envelope, matching the existing streaming translation behavior. It also adds robust parsing for tool-call arguments and comprehensive unit tests in tests/unit/nonstreaming-gemini-family-response-projection.test.ts to prevent regression. No review comments were provided, so there is no additional feedback to address.

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[diegosouzapw]

Aprovado. Rodei o probe: 3/3 testes passam com a correção e os 3 falham revertendo só o hunk de produção (fail-without-fix confirmado). Suíte de regressão plan3-p0 (38/38) segue verde. Conferi a colisão com #7207 — arquivos distintos (streaming vs non-streaming), sem sobreposição textual. Pronto para merge.