fix(verl): decode file URIs before loading images

[Jialiang Liang (lux-liang)]

Fixes #637.

Images referenced with Path.as_uri() can be dropped from training because the loader passes the escaped URI path directly to Pillow. Convert file URIs with url2pathname before opening them so local paths, spaces, Unicode, and literal percent sequences are handled correctly.

The regression tests use actual PNG files and check that the public rollout adapter keeps the training row. A literal %20 filename has a distinct alternate file to detect accidental double decoding. The multimodal example now shows how to construct local image URIs.

Validation:

• On Ubuntu/WSL with Python 3.12.3 and the frozen verl-cpu environment: uv run --locked --no-sync pytest -v --durations=20 tests passes all 143 tests, and uv run --locked --no-sync pyright reports no errors or warnings.
• Before the fix: all five new file-URI cases fail. After the fix: uv run --locked --no-sync pytest -q tests/verl/test_rollout_adapter.py --tb=short passes all 22 tests.
• An independent offline probe with real CLIPProcessor, Pillow, Torch CPU, and VERL confirms that equivalent data and file URIs now preserve the same training sample.
• uv run --locked --no-sync pre-commit run --all-files --show-diff-on-failure, ruff check ., ruff format --check ., and python scripts/check_headers.py pass.
• uv run --locked --no-sync mkdocs build --strict, uv build --no-sources, and archive-content checks pass.

Additional native Windows checks produced 134 passing tests and nine existing controller failures involving os.killpg, plus three existing os.killpg/signal.SIGKILL type errors. The exact original base produces the same failures and diagnostics; all controller tests and the original type check pass on Linux. WSL tests use a native Linux temporary directory because NTFS-backed temporary-file truncation fails before pytest collection.

No GPU training or network-share access was tested. AI assistance: this change and its tests were prepared with Codex and independently checked by another Codex agent.

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[Copilot]

🟢 Approval recommended

The focused implementation correctly handles native paths and is covered by representative regression tests.

0 open findings

What changed in this PR

Fixes local file URI image loading in the VERL rollout adapter by converting encoded URI paths to native filesystem paths.

Changes:

• Decode file URI paths using url2pathname.
• Add regression coverage for spaces, Unicode, percent literals, and retained training rows.
• Document constructing local image URIs with Path.as_uri().

File	Description
agentlightning/​verl/​rollout_adapter.py	Converts file URIs before opening images.
tests/​verl/​test_rollout_adapter.py	Tests URI decoding and training-row retention.
docs/​80-example-multimodal-qa.md	Documents local image URI construction.

🧠 Review effort: Balanced

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[Zhiyuan He (hzy46)]

Thanks. Please sign the Contributor License Agreement then I can merge this PR.