Previously `isPureJjRepo` returned true whenever the resolved jj and git roots merely differed. That punishes the legitimate inverse-nesting case: a real git checkout (vendored repo, fixture, independent nested checkout) living UNDER an outer pure jj workspace. Both `jj.repo.root` and `git.repo.root` walk upward from cwd and return the closest ancestor — so the deeper root is the one the user is actually working inside, and Git automation against the inner checkout never touches the surrounding jj tree.
`isPureJjRepo` now returns true iff jj is the *deeper* ancestor (or no git is present at all). The new `isStrictDescendant` helper does the depth check via `path.relative`. Added unit + integration tests covering both nesting directions on all three surfaces (`utils/jj`, `task/worktree`, `autoresearch/git`).
Refs #1935
Previously `getRepoRoot` and `ensureAutoresearchBranch` only consulted `jj.isPureJjRepo` after `git.repo.root` returned null. For a jj workspace nested under an unrelated outer Git checkout, `git.repo.root` walks up and finds the outer .git, so the pure-jj branch never fired and isolation/autoresearch silently mutated the surrounding Git tree behind jj's back.
Both call sites now run the pure-jj guard first, rejecting at the jj workspace's own root regardless of any surrounding Git checkout. Added integration tests for the nested case on both surfaces.
Refs #1935
Worktree setup and autoresearch Git prep silently misbehaved in pure Jujutsu workspaces (`.jj/repo/` present, no colocated `.git/`):
- `task/worktree.ts#getRepoRoot` threw a generic "Git repository not found for isolated task execution.", giving a jj user no hint about what was wrong.
- `autoresearch/git.ts#ensureAutoresearchBranch` returned a soft "Not in a git repository" warning, letting `/autoresearch` proceed with no branch isolation, baseline reset, or auto-commits.
Both paths now detect a pure jj workspace via a new `jj.isPureJjRepo` helper and surface an actionable Jujutsu-specific error pointing at `jj git init --colocate`. Colocated jj-git workspaces (both `.jj/` and `.git/` at the same root) and plain Git checkouts behave exactly as before.
Fixes#1935
roboomp