Merge prgs/master into feat/issue-274-branches-only-worktrees; keep both
already_landed_reconcile and author_mutation_worktree imports. Allow
branches/ worktrees when PROJECT_ROOT is the session worktree; align
commit-payload tests with branches-only guard (#274).
Add author_mutation_worktree assessment and integrate it into MCP
preflight so author mutations fail closed outside branches/ session
worktrees, with tests for control-checkout and branches-path cases.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>