[BUG] Missing UI warning when MCP images are omitted for exceeding limits

[weimar-torres-herrera]

Issue

When an MCP tool result includes images that exceed the limits defined in model-output.ts (per-image size, image count, or total combined size), those images are silently omitted. The event is logged, but no warning is shown to the user in the UI, giving the impression that all images were processed correctly when some are actually missing.

How to reproduce

1. Run an MCP tool that returns images exceeding one of these limits (defined in model-output.ts:8):
   • MCP_DIRECT_IMAGE_MAX_BYTES (10 MB per image)
   • MCP_IMAGE_MAX_MEDIA_PARTS (16 images per result)
   • MCP_IMAGE_MAX_TOTAL_BYTES (25 MB total)
2. For example: send 20 images of 1 KB each (exceeds the count limit), or 4 images of 7 MB each (exceeds the total size limit).
3. Check the UI where the tool result is displayed.
4. Notice there's no indication that any images were omitted.

Expected Behavior

When one or more images are omitted due to exceeding a limit, the UI should display a visible warning to the user (e.g. "N images were omitted for exceeding the size/count limit"), instead of this information being available only in server logs.

Screenshots

...

Platform

• npx / Desktop App

Additional Context

I verified the behavior of all three limits using a test fixture, and in all cases the backend correctly applies the omission logic (as recorded in the logs):

• 1 image of 11 MB → 0 accepted | image omitted: image/png exceeds 10 MB limit
• 20 images of 1 KB → 16 accepted, 4 omitted | image omitted: image count exceeds 16 limit
• 4 images of 7 MB → 3 accepted, 1 omitted | image omitted: total image bytes exceed 25 MB limit
• 6 images of 60 KB → 6 accepted, 0 omitted (no issue in this case)

The limit logic itself works correctly — the issue is the lack of user-facing feedback when an omission occurs.

[dosubot]

@weimar-torres-herrera, I traced through the omission path and can confirm your analysis is accurate — there is genuinely no code path that surfaces image-omission information to the user.

The limits in model-output.ts are enforced correctly. When an image exceeds a limit, mapImageData returns a synthetic text part like [image omitted: image/png exceeds 10 MB limit] instead of the image [1]. The problem is that this marker is treated as an internal signal, never user-facing:

1. Server side — isImageOmissionMarkerText and isModelVisibleImageOutput use the "[image omitted:" / "[resource link omitted:" prefixes only to decide whether to replay the raw MCP result vs. the model-facing output. They never emit a notification [2] [3].

2. Client preview resolver — mediaPartsToPreviews filters the model output to only type: "media" image parts and silently discards everything else, including the omission-marker text parts [4].

3. Rendering — McpToolResultImagePreviewGrid renders only the resolved previews array with no branch for omission markers or dropped-image counts [5]. ToolPart delegates entirely to this grid and the preview hook [6].

So the omission text only ever lives in the raw tool-result JSON — it never reaches any visible UI element. A fix would involve having the preview resolver (or ToolPart) count "[image omitted:" markers in the model output content parts and render an inline notice alongside the image grid.

To reply, just mention @dosu.

---

Share context across your team and agents. Try Dosu.