image-generation-via-a2a

name	image-generation-via-a2a
description	When a slides deck needs images, delegate to the Assets app over A2A so generations are grounded in the user's brand library — never call an image-generation API directly from slides.

Image generation via A2A

Slides never calls an image-generation API itself when Assets is reachable. Assets owns brand libraries, presets, provenance, and the generation audit log, so every improvement there has to reach decks for free.

Both entry points share one delegation helper, server/lib/assets-image-delegation.ts:

1. generate-image-api — the action the agent and the editor's image panel use. It delegates to Assets, then returns source: "assets-a2a" with the Assets reply verbatim (plus url when a previewUrl/downloadUrl was parseable).
2. pnpm action generate-image — the CLI script, for local runs that want files on disk. Same delegation, prints the reply verbatim.

The helper resolves Assets through agent discovery (target assets, which also matches images), so a workspace with both apps mounted needs no configuration. IMAGES_A2A_URL / IMAGES_A2A_KEY remain as overrides for standalone deploys that point at a remote Assets instance.

Outcomes

The helper distinguishes four outcomes, because "Assets did not return an image" has very different right answers:

Outcome	Meaning	What happens
delegated	Task completed	Use the reply's previewUrl
rejected	Task ended failed/canceled/input-required	Surface the reason; do NOT silently generate locally
pending	Caller-side timeout; the Assets run is still going and owns a taskId	Tell the user to check Assets; generating again would duplicate the run
unavailable	Assets could not be resolved or reached at all	Local fallback

Only unavailable falls through to the local Gemini/OpenAI providers under server/handlers/image-providers/, so a slides-only deploy still works. That output is not brand-grounded and the action says so: it returns source: "slides-fallback" with a fallbackReason. Report that honestly rather than presenting a fallback image as a library generation.

There is no direct Builder.io image-generation path in slides. If a user wants Builder-managed generation, that belongs in Assets, behind the same delegation.

Calling explicitly from the agent

Call the action with the destination so Assets can ground the generation:

generate-image-api { prompt, deckId, slideId, slideContent }

For direct insertion, add insertIntoSlide: true. This requires both IDs and only returns inserted: true after Slides writes the transformed HTML through update-slide and re-reads it through get-deck with compact=false to find the image source. Never say the image was added based on url, previewUrl, or a completed Assets reply alone. For preview-only variations, leave insertIntoSlide false; after choosing one, use update-slide and verify the persisted source with get-deck with compact=false before claiming insertion.

Do not reach for the generic call-agent tool to ask Assets for an image. It talks to the same app, so it looks equivalent, but it skips the slide grounding, the completed-vs-failed task handling, and the ready-to-render preview markdown this action returns — which is how image results end up in chat as bare links instead of visible images.

Slides owns the semantic job of the image: its slide role, audience, crop, and must-preserve content. Assets owns library and preset selection, style anchors, generation settings, and provenance. Include the active design system's image-style guidance in the prompt context, but do not ask Assets to invent a competing brand direction.

Use the returned previewUrl for previews. Do not drop it into slide HTML without the verified insertion workflow above.

Showing the result in chat

Always show a generated image as an inline markdown image:

![Monstera deliciosa](https://…/preview.png)

The chat renders ![]() as a real image but []() as a bare link, so a plain link (or a "View the photo" / "Open preview" link) leaves the user with nothing to look at. Use the action's url field, or the previewUrl from the Assets reply when the action could not parse one. This applies whether the request came from the editor's image panel or from a plain chat message like "generate a photo of a monstera".

The delegation message already instructs Assets to mark generations with source: "a2a" and callerAppId: "slides" when it calls generate-image-batch or refine-image. That keeps the Assets audit log useful for design review.

Multi-slide image generation

Do not fire parallel add-slide calls into the same deck. Keep deck writes sequential: add one slide, wait for the result, then add the next slide. If a single slide needs several image variants, the image-generation action may request multiple variants internally, but the deck write itself should remain a single add-slide or update-slide call.

Iteration

When the user gives feedback ("make slide 3's hero darker, more navy"), ask Assets to run refine-image with the previous assetId (extracted from the previewUrl returned earlier) plus the new feedback. Replace only the slide-3 <img src="..."> with the new URL. Do not delete the prior asset — it stays in the library so the user can pick which version to keep.

Cross-app reply parsing

The Assets reply comes back as plain text. Assets (per its a2a-assets skill) includes assetId, runId, previewUrl, downloadUrl, and embedPath exactly as returned by its actions. extractAssetUrl pulls the first previewUrl / downloadUrl out of that reply; when it finds none, the action returns the reply without a url.

If parsing the reply fails, surface "I couldn't parse the Assets agent's response" to the user rather than guessing at URLs.