## Motivation
Models that only support image editing (ImageToImage but not
TextToImage) would silently attempt text-to-image generation when a user
submitted a text prompt without an attached image
## Changes
- Added an early return guard in handleSubmit() that prevents submission
when the selected model only supports image editing and no image is
attached (isEditOnlyWithoutImage)
- Fixed the text-to-image generation branch to use the more specific
modelSupportsTextToImage() check instead of the broad isImageModel(),
ensuring only models with TextToImage capability trigger generation from
text alone
- The existing isEditOnlyWithoutImage derived state (which was already
used for UI hints like placeholder text and button disabling) now also
blocks the actual submit path
## Why It Works
The text-to-image fallback now correctly checks
modelSupportsTextToImage() directly, so edit-only models no longer fall
through to the generation path
## Test Plan
### Manual Testing
- Select an edit-only image model (e.g., one with only ImageToImage
capability)
- Verify the send button is disabled and placeholder reads "Attach an
image to edit..." when no image is attached
- Attach an image and verify the form becomes submittable
- Select a text-to-image model and verify text-only prompts still
trigger generation normally
- Ensure pressing `enter` doesn't bypass check
ciaranbor
b61dc2eb35
