Idea branches

Choice: an idea's docs land on main early, by small PRs, with status: draft | accepted | shipped | dropped. Code branches stay short and carry the idea ID (IDEA-0010-paywall), which links them to the idea (canon-web, FEAT-0012). "Completed ideas" is the Ideas board filtered to shipped, not a branch. Why: an idea branch hides the PRD, RFC and findings from search and from canon-web (which shows merged main only) while they are being discussed. Branches that live for weeks drift from main. A dropped idea's findings would go with its branch. Git cannot merge several repos at once. Ideas ship over several releases. For one person with agents, an extra branch layer slows shipping (C-01). Rejected: an idea branch in every repo the idea touches, holding its PRD, RFC, findings, designs and tasks, merged to main when the idea is done (deferred 2026-10-29: the reasons above, plus worktrees for parallel ideas and conflicts on the wiki index, canon.yaml and the IDEA counter). Revisit: when a team needs nothing half-done on main and feature flags cannot give it that.