Shared HTTP-header builder for Gemini provider adapters. See spec §32.1 (bundled adapters) and the Phase 16 design's Decision #2.

Layer B helper. Both the chat adapter (ALLM.Providers.Gemini) and the image adapter (ALLM.Providers.Gemini.Images, Phase 16.5) inject the same x-goog-api-key and content-type: application/json headers.

Per the Phase 16 design's Decision #2: the API key flows on the x-goog-api-key request header, not the ?key=... query parameter. Both forms are documented and equivalent server-side; the header form keeps the API key out of HTTP access logs and metrics.

Per Decision #3: the same header is also the streaming-endpoint authentication; streamGenerateContent?alt=sse accepts identical headers — only the URL's ?alt=sse query param differs.

Examples

iex> ALLM.Providers.Support.GeminiHeaders.headers("AIza-test")
[{"x-goog-api-key", "AIza-test"}, {"content-type", "application/json"}]