Spec Kitty

Data Model: Single-branch topology honesty and destroyed-lane tip guard

meta.json (mission metadata)

This mission adds or changes the following fields.

Field	Type	Presence	Written by	Rule
topology	enum `single_branch \	lanes \	coord \	lanes_with_coord`
commit_to_target	bool	absent by default; written only as true	mission create (--commit-to-target)	A non-boolean value fails closed and is never truthiness-coerced. It mirrors the pattern in read_retention_from_meta.
mission_branch	str	only for a protected-target single_branch mission without commit_to_target	mission create	Set to kitty/mission-<slug>-<mid8>. Create refuses if the branch already exists. Readers key on topology and this field, never on ref shape.

Invariant T-1: topology == single_branch implies lanes.json has no code lane. A violation fails closed at the writers with SINGLE_BRANCH_CODE_LANES_UNMIGRATED.

lanes.json (lane manifest)

• single_branch:
• lanes holds exactly one lane, lane_id = "lane-planning", and its wp_ids is every work package in the mission.
• is_repo_root_lane(lane) is true for it.
• is_planning_artifact_only(manifest) is true only when every work package is a planning_artifact.
• lanes / flat: unchanged.
• has_code_lanes(manifest): true when any lane is not the repo-root lane. The topology derivation reads only this.

Lane work-tip record

• Name: refs/spec-kitty/lane-tip/<lane-branch>, where <lane-branch> is the full branch name, for example kitty/mission-foo-01ABCDEF-lane-a.
• Value: the SHA of the last observed commit on that lane branch.
• Writers:
• the post-commit recorder, for any commit whose HEAD is a kitty/mission--lane- branch;
• spec-kitty lane advances: allocation, reuse, dependency merge, auto-rebase, for_review, and safe_commit;
• backfill on touch.
• Deleters: a work package reaching a terminal state (done, canceled) with no other non-terminal work package in the lane; consolidation teardown of the lane.
• Local only: the ref is never pushed.

Guard decision table

The guard runs at implement when neither the lane branch nor its worktree exists.

WP state	Tip ref	Absorbed?	Result
any other state	any	—	proceed (FRESH)
trigger state†	absent, no context	—	proceed (a genuinely fresh lane)
trigger state†	absent, context present	—	refuse LANE_WORK_TIP_UNKNOWN
trigger state†	present	yes (ancestor, equals base, or merge-tree no-op)	proceed
trigger state†	present	no	refuse DESTROYED_LANE, naming the SHA and git branch <b> refs/spec-kitty/lane-tip/<b>
trigger state†	present	cannot evaluate (git < 2.38)	refuse (fail closed)

† Trigger state means {in_progress, blocked, for_review, in_review} (plan fold M7; analysis finding T1). Every other state proceeds (FRESH).

Coord topology keeps its existing #4889 behaviour: its check on the unreachable base still fires first.

ResolvedWorkspace

• New property status_execution_mode: "direct_repo" when resolution_kind == "repo_root", else "worktree".
• New input effective_root: Path | None, taken from PR #5009. For single_branch, worktree_path is effective_root or, when that is absent, the repository root.

WorkspaceContext (.kittify/workspaces/*.json)

• The schema is unchanged.
• Writes are centralised in allocate_lane_worktree (FR-022).

Status event

• execution_mode is taken from ResolvedWorkspace.status_execution_mode on every transition path.

Doctor findings (topology audit)

Code	When	Remedy
SINGLE_BRANCH_CODE_LANES_UNMIGRATED	topology == single_branch and has_code_lanes(lanes.json)	spec-kitty upgrade (runs the re-stamp) or spec-kitty migrate backfill-topology --restamp-single-branch