Gates Taxonomy

Canonical gate types used across GSD workflows. Every validation checkpoint maps to one of these four types.

Gate Types

Pre-flight Gate

Purpose: Validates preconditions before starting an operation. Behavior: Blocks entry if conditions unmet. No partial work created. Recovery: Fix the missing precondition, then retry. Examples:

Plan-phase checks for REQUIREMENTS.md before planning
Execute-phase validates PLAN.md exists before execution
Discuss-phase confirms phase exists in ROADMAP.md

Revision Gate

Purpose: Evaluates output quality and routes to revision if insufficient. Behavior: Loops back to producer with specific feedback. Bounded by iteration cap. Recovery: Producer addresses feedback; checker re-evaluates. The loop also escalates early if issue count does not decrease between consecutive iterations (stall detection). After max iterations, escalates unconditionally. Examples:

Plan-checker reviewing PLAN.md (max 3 iterations)
Verifier checking phase deliverables against success criteria

Escalation Gate

Purpose: Surfaces unresolvable issues to the developer for a decision. Behavior: Pauses workflow, presents options, waits for human input. Recovery: Developer chooses action; workflow resumes on selected path. Examples:

Revision loop exhausted after 3 iterations
Merge conflict during worktree cleanup
Ambiguous requirement needing clarification

Abort Gate

Purpose: Terminates the operation to prevent damage or waste. Behavior: Stops immediately, preserves state, reports reason. Recovery: Developer investigates root cause, fixes, restarts from checkpoint. Examples:

Context window critically low during execution
STATE.md in error state blocking /gsd-next
Verification finds critical missing deliverables

Gate Matrix

Workflow	Phase	Gate Type	Artifacts Checked	Failure Behavior
plan-phase	Entry	Pre-flight	REQUIREMENTS.md, ROADMAP.md	Block with missing-file message
plan-phase	Step 12	Revision	PLAN.md quality	Loop to planner (max 3)
plan-phase	Post-revision	Escalation	Unresolved issues	Surface to developer
execute-phase	Entry	Pre-flight	PLAN.md	Block with missing-plan message
execute-phase	Completion	Revision	SUMMARY.md completeness	Re-run incomplete tasks
verify-work	Entry	Pre-flight	SUMMARY.md	Block with missing-summary
verify-work	Evaluation	Escalation	Failed criteria	Surface gaps to developer
next	Entry	Abort	Error state, checkpoints	Stop with diagnostic

Implementing Gates

Use this taxonomy when designing or auditing workflow validation points:

Pre-flight gates belong at workflow entry points. They are cheap, deterministic checks that prevent wasted work. If you can verify a precondition with a file-existence check or a config read, use a pre-flight gate.
Revision gates belong after a producer step where quality varies. Always pair them with an iteration cap to prevent infinite loops. The cap should reflect the cost of each iteration -- expensive operations get fewer retries.
Escalation gates belong wherever automated resolution is impossible or ambiguous. They are the safety valve between revision loops and abort. Present the developer with clear options and enough context to decide.
Abort gates belong at points where continuing would cause damage, waste significant resources, or produce meaningless output. They should preserve state so work can resume after the root cause is fixed.

Selection heuristic: Start with pre-flight. If the check happens after work is produced, it is a revision gate. If the revision loop cannot resolve the issue, escalate. If continuing is dangerous, abort.