Checkpoint 2 — reliable paired-file navigation

[GeoffRiley]

Outcome

Transcribe a directory of sequential images without manually reopening or matching each text file.

Exit checks

• Discover supported image formats and order numbered filenames naturally.
• Pair same-basename .md or .txt files and create a missing counterpart safely.
• Previous/next navigation keeps the correct image and transcription together.
• Report .md/.txt conflicts rather than silently choosing one.
• External edits and unsaved changes are detected before overwrites.
• Exercise the two sample pages plus a folder with missing and conflicting counterparts.

Evidence

Link focused tests for pairing and save conflicts plus a manual walkthrough.