CLI encode:
- Auto-detect output format from extension (.jpg → DCT mode, .png → LSB)
- Default to JPEG output for JPEG carriers (preserves DCT benefits)
- Pass embed_mode and dct_output_format to encode function
jpegtran fix (critical for rotation fallback):
- Remove -trim flag which was dropping edge blocks and destroying stego data
- Remove -perfect flag which fails on non-MCU-aligned images
- Plain jpegtran without flags works correctly for lossless rotation
This enables: encode → external rotation → decode to work correctly.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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