v0.7.5

Fixed

• Inbound image MIME type was discarded and rewritten as JPEG — both engine::extract_image_parts and the per-block path inside session_prompt had only kept the base64 data and hard-coded data:image/jpeg;base64,… when forwarding to OpenAI-compatible backends. Any ACP/A2A client sending PNG/WebP/GIF content was therefore mislabeled, which can break vision-model decoding or yield undefined multi-modal behaviour. Image extraction now returns a new ImageBlock { data, mime_type }, the per-block mimeType is threaded through, and session_prompt emits data:<mime>;base64,<data> using the client's declared MIME (with image/jpeg only as a fallback for clients that omit the field). Reviewer-flagged by Eren.
• A2A transport silently dropped image inputs — handle_message_send only extracted text from message.parts and always called engine::session_prompt(..., &[], None), so text+image A2A requests lost their images and image-only A2A requests were rejected as empty. initialize() already advertises agentCapabilities.promptCapabilities.image: true, so the A2A path now honors it: both text and image parts are extracted, an empty prompt is rejected only when both are absent, and images are forwarded to session_prompt. Reviewer-flagged by Eren.