[sanskarIN]

Finding

ThumbnailProvider::requestImageResponse() previously passed Qt Quick's requested thumbnail size directly to MLT/FFmpeg or still-image decoding, with no upper bound. A very large UI-provided size can drive disproportionate image/decoder allocations, even when the actual displayed thumbnail is small. The waveform provider already caps requests; the thumbnail provider did not.

This is independent memory-pressure hardening related to the editor crash investigations, not a demonstrated root cause of #175 or #185.

Changes

• Introduce ThumbnailProvider::boundedRequestSize().
• Preserve small, valid requests exactly (no unintended upscale).
• Cap the largest requested image to 1920×1080 pixels, proportionally scaling down larger dimensions.
• Invalid or zero dimensions fall back to 192×108.
• Apply the same bound to ordinary cached thumbnails and source-excerpt frame requests before starting asynchronous decoder work.
• Add a focused Qt test covering normal, invalid, 4K and extreme 100k-pixel requests.

Verification

• Formatting / CMake test registration
• Linux debug / static analysis and AddressSanitizer + UBSan
• Windows MSYS2 tests and Windows packaged-binary verification
• Review UI requests for unexpected aspect-ratio changes

No release or tag created; user-adjustable export FPS and project data remain unchanged.