[Huge]

Summary

Validates and sanitizes bg_color in GreenScreenProcessor (tools/video/green_screen_processor.py) to prevent FFmpeg filter graph injection.

Previously, bg_color was only stripped of # (bg_color.lstrip("#")) and directly interpolated into the filter graph string in _process_chromakey():
f"color=c=0x{bg_hex}:size={width}x{height}"
If an attacker supplied a crafted bg_color string containing filter graph delimiters (such as commas, colons, or filter expressions like 000000,drawbox=...), arbitrary FFmpeg filter chains could be injected.

Changes

• Added _validate_hex_color(bg_color: str) -> str to enforce strict 3, 6, or 8 character hexadecimal formatting and expansion (e.g. 000 -> 000000).
• Validated bg_color upfront in execute() so invalid color inputs return a clean ToolResult(success=False, error=...) without launching subprocesses.
• Applied validation in _process_chromakey() and _process_rembg() before passing into FFmpeg filter graph definitions or slicing RGB channels.
• Added comprehensive unit tests in tests/tools/test_green_screen_chromakey.py covering valid colors and rejecting filter injection payloads / malformed hex values.

Testing

• Ran focused unit tests:
  uv run --with pytest pytest tests/tools/test_green_screen_chromakey.py (18 passed)
• Ran contract test suite:
  uv run --with-requirements requirements-dev.txt --with filelock pytest tests/contracts/ (1229 passed, 7 skipped)

Checklist

• The change is focused on a single logical concern.
• I ran the relevant tests locally (make test-contracts / make test) where applicable.
• I updated docs/README if behavior or usage changed.
• No unrelated files (build artifacts, local config) are included in the diff.

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Disclaimer: Vulnerability spotted while test-driving BudgetScan https://huge.github.io/nano-analyzer static analysis. Fix human-verified.

[Huge]

Gentle ping on this one: it validates bg_color before the green-screen tool puts it into the FFmpeg filter graph. Is anything missing before it can be reviewed?

[calesthio]

Thank you for validating background colors before filter construction. Reviewed the complete diff against main 63d1087a: accepted 3/6/8-digit hex forms are normalized, invalid/filter syntax is rejected before subprocess launch, and both background-removal paths use the validation. Validation: isolated offline suite — 18 passed, including native FFmpeg chroma-key rendering.