Summary

Implement the MilestoneStrategy for the pluggable ceremony scheduling system.

Ceremonies fire at semantic project milestones rather than task counts or time. Milestones are defined as tags on tasks or task groups.

Design Reference

See Ceremony Scheduling design page -- "Milestone-Driven" strategy section.

Key Behaviors

• should_fire_ceremony: checks if all tasks tagged with a configured milestone are complete
• should_transition_sprint: at a configured milestone (e.g., all tasks tagged release_candidate complete)
• on_task_completed: evaluates milestone completion state
• on_task_added: re-evaluates milestone membership
• Default velocity calculator: PointsPerSprintVelocityCalculator

Strategy Config

strategy_config:
  milestones:
    - name: feature_complete
      ceremony: sprint_review
    - name: code_freeze
      ceremony: retrospective
    - name: release_candidate
      ceremony: sprint_planning

Prerequisites

Requires a task tagging/grouping mechanism to define milestone membership. This may need a small extension to the Task model or a separate milestone registry.

Implementation

• New: src/synthorg/engine/workflow/strategies/milestone_driven.py
• New: tests/unit/engine/workflow/strategies/test_milestone_driven.py
• Implement CeremonySchedulingStrategy protocol from feat: sprint ceremony runtime scheduler with task-driven cadence support #961

Dependencies

• feat: sprint ceremony runtime scheduler with task-driven cadence support #961 (protocol interfaces + reference implementation)