nx_jpeg_ascii.nx

nx_jpeg_ascii.nx -- bridge: baseline-JPEG bytes -> luminance ASCII. Decodes a baseline JPEG, takes the Y (luma) plane, box-downscales it to (target_w x target_h), and writes it into a caller Framebuffer as grayscale RGBA so nx_paint_fb_ascii_dump / _write can render the image in a terminal. This is the last brick of the image pipeline: real bytes off the wire -> visible pixels, every layer NishiLang. Why luma-only: ASCII art needs luminance, and the JPEG Y component IS luminance at full resolution. We deliberately skip chroma upsample + YCbCr->RGB -- fewer bytes between the silicon and the pixel, exactly the bits-up discipline. A future colour path (ANSI true-colour cells) composes the existing nx_jpeg_upsample + nx_jpeg_ycbcr bricks on top of this same decode. hardens: CVE-2014-9707 (libjpeg-turbo MCU overflow on malformed DCT) -> dimensions bounded by NX_JPEG_ASCII_MAX_DIM with a sealed OVERSIZE verdict BEFORE any plane allocation. CVE-2018-13785 (libpng length-add integer overflow) -> i64 dims + explicit bound check before alloc; never trust attacker-supplied dimensions to fit a budget. NISHI_BROWSER_KNOWN_LESSONS.md §4 (image decoders) + §12 (bounded loops): every loop below is bounded by image or target dimensions; no open-ended scan. genealogy_id: nishi_browser_image_pipeline_phase_5 lineage_id: nishi_jpeg_ascii_v1 license_tier: ORIGINAL