PR-preparation tasks could never attach an isolated execution workspace
on a pre-existing branch: child-issue creation inherited the source
issue's workspace binding (often the shared primary checkout), and the
worktree runtime only knew template-derived branch names, silently
creating a fresh branch off base when the rendered name did not exist.
Add workspaceStrategy.existingBranch as the smallest explicit contract:
- Shared type + issue validator accept the pin only with isolated mode
and a git_worktree strategy, reject branchTemplate alongside it, and
validate the branch-name shape.
- realizeExecutionWorkspace gains an exact-branch mode: verify the
branch exists (fail closed otherwise), reuse a registered worktree
that already has it checked out (including legacy .worktrees/ paths),
otherwise attach it under the managed worktree parent without -b.
Exact mode never creates, renames, fast-forwards, resets, or
reconciles the requested branch, and never falls back to
project_primary or a derived branch.
- Dispatch ignores an inherited reuse_existing workspace binding whose
recorded branch does not equal the pinned branch and realizes the
pinned branch instead.
- scripts/repair-pr-prep-workspace-attachment.mjs converts stranded
PR-prep issues to the new contract via the company-scoped API without
touching any git branch.
Co-authored-by: Paperclip <noreply@paperclip.ing>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
