feat: Add support for VertexAI compatible service (#375)

refactor(executor): dedupe thinking metadata helpers across Gemini executors

Merge pull request #376 from auroraflux/feat/reasoning-suffix-support

**feat(util): add -reasoning suffix support for Gemini models**

**fix(executor, auth): ensure index assignment consistency for auth objects**

fix(claude): ensure max_tokens exceeds thinking budget for thinking models

Fixed: #339

Fixed: #337

Merge branch 'dev' into feat/claude-thinking-and-beta-headers

**fix(executor): comment out redundant code for setting Claude system instructions**

feat(claude): add thinking model variants and beta headers support

**fix(executor): update antigravity executor to enhance model metadata handling**

**fix(translator): reintroduce `thoughtSignature` bypass logic for model parts**

fix(aistudio): strip Gemini generation config overrides

**chore(executor): update default agent version and simplify const formatting**

**feat(executor, translator): enhance token handling and payload processing**

**feat(executor): add model alias mapping and improve Antigravity payload handling**

fix(gemini): parse stream usage from JSON, skip thoughtSignature

fix(gemini): filter SSE usage metadata in streams

fix(runtime): treat non-empty finishReason as terminal

fix(executor): expire stop chunks without usage metadata

feat(runtime): track antigravity usage and token counts

fix: handle empty and non-JSON SSE chunks safely

fix: preserve SSE usage metadata-only trailing chunks

fix(sse): preserve usage metadata for stop chunks

Fixed: #302

**feat(translator): add Antigravity translation logic**

feat(executor): share SSE usage filtering across streams

**feat(auth, executor, cmd): add Antigravity provider integration**

Fixed: #291

**refactor(executor): simplify Gemini CLI execution and remove internal retry logic**

fix(executor): prevent streaming on failed response when no fallback

fix(executor): prevent streaming from 429 response when fallback available

feat(executor): add intelligent retry logic for 429 rate limits

**feat(registry): add GPT-5.1 Codex Max model definitions and support**

**feat(auth): add AuthIndex for diagnostics and ensure usage recording**

fix: detect HTML error bodies without text/html content type

feat(auth): add iFlow cookie-based authentication support

**fix(runtime): simplify scanner buffer allocation in executor implementations**

**refactor(runtime): centralize reasoning effort logic for GPT models**

fix(runtime): remove gpt-5.1 minimal effort variant

**feat(runtime): extend executor support for GPT-5.1 Codex and variants**

**feat(runtime): add payload configuration support for executors**

Fixed: #246

feat(gemini-cli): add multi-project support and enhance credential handling

feat(vertex): add usage source resolution for Vertex projects

feat(vertex, management): enhance token handling and OAuth2 integration

feat(vertex): add support for Vertex AI Gemini authentication and execution

fix(executor): ensure usage reporting for upstream responses lacking usage data

feat(config): support HTTP headers across providers