Step-by-step TDD plan for the login + critical-bug-fix phase. Eleven tasks, each with file:line targets, complete code blocks, test code, and exact verification commands. Lands diagnostic logging, login/ authorize envelope enrichment, author/series ID surfacing, filterdata hydration, resume-position wire-up, POST /auth/refresh, and POST /logout. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>