With the 2473 gap (second of the hour, third of the session including the earlier 2466 skip), the Echoes chapter-numbering issue is now clearly systematic rather than incidental. All three gaps were caught by Opus 4.8 before publication, but the frequency — roughly one gap per 15-20 chapters at current velocity — suggests Gemini 2.5 Pro's chapter-numbering process needs a structural fix. Possible causes: context-window counter drift, Git commit-then-skip pattern, or mental-model desynchronization between "chapters written" and "chapters committed."