feat: allow images as urls for supported backends

[AngeloDanducci]

Pull Request

Issue

Fixes #127

Description

allows images as urls for supported backends

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used

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[planetf1]

One test regression and a docstring gap to fix before merge, plus a couple of things worth flagging.

Test assertion needs updating (test/backends/test_vision_openai.py:163–164): The ollama version (test_vision_ollama.py:148–150) was updated to pull out first_image and compare .value, but the OpenAI test still compares last_action.images[0] directly against image_block.value. Since images now returns block objects, this is comparing an ImageBlock to a str and will fail when the e2e test runs:

    # first image in image list should be the same as the image block
    first_image = last_action.images[0]  # type: ignore
    assert isinstance(first_image, ImageBlock)
    assert first_image.value == ImageBlock.from_pil_image(pil_image).value

Raises: entry missing (mellea/backends/ollama.py:366–367): generate_from_chat_context now raises ValueError for ImageUrlBlock, but the docstring only lists RuntimeError. Per AGENTS.md (Section 10, item 6) every raise in a public function wants a matching entry — the quality gate won’t catch this one since RuntimeError is already listed:

        Raises:
            RuntimeError: If not called from a thread with a running event loop.
            ValueError: If a message contains an ``ImageUrlBlock``; Ollama requires
                base64-encoded images — convert to an ``ImageBlock`` first.

Breaking change: Message.images now returns list[ImageBlock | ImageUrlBlock] rather than list[str]. Right call, but worth a line in the PR description and a changelog entry so people know to expect it on upgrade.

Missing tests: Three new paths that’d be worth covering before this merges, since they’re the heart of the feature:

• get_image_blocks() with an https:// URL returning an ImageUrlBlock — the http/https branch at cli/serve/models.py:89–90 isn’t exercised yet (the existing pydantic-parse test only checks the model deserialises)
• Ollama rejecting an ImageUrlBlock with ValueError — the guard at ollama.py:401–402 has no test
• message_to_openai_message passing a URL straight through as {"image_url": {"url": ...}} instead of wrapping it in a data URI (openai_compatible_helpers.py:200–206) — nothing hits that branch currently

[planetf1]

Nit: ImageUrlBlock is already imported at runtime on line 11, so the copy in the TYPE_CHECKING block is dead. Ruff doesn’t flag it across the guard, but it reads as if it’s type-only.

Suggested change

	from ..core.base import AbstractMelleaTool, ImageUrlBlock, ModelOutputThunk
	from ..core.base import AbstractMelleaTool, ModelOutputThunk