Summary

Implement the BudgetDrivenStrategy for the pluggable ceremony scheduling system.

Ceremonies fire at cost-consumption thresholds. Ties directly into the existing budget module (cost tracking, quota degradation, CFO optimization).

Design Reference

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

Key Behaviors

• should_fire_ceremony: checks if context.budget_consumed_fraction has crossed a configured threshold (e.g., 25%, 50%, 75%)
• should_transition_sprint: returns IN_REVIEW when budget is exhausted (100% consumed) or configured budget threshold is crossed
• on_budget_updated: tracks budget consumption for threshold evaluation
• Other hooks: no-op
• Default velocity calculator: BudgetVelocityCalculator (pts/EUR)

Implementation

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

Also implement: BudgetVelocityCalculator

• New: src/synthorg/engine/workflow/velocity_calculators/budget.py
• New: tests/unit/engine/workflow/velocity_calculators/test_budget.py
• Primary unit: pts/EUR (uses default display currency from budget config)
• Requires VelocityRecord.budget_consumed field (added in feat: sprint ceremony runtime scheduler with task-driven cadence support #961)

Integration Points

• src/synthorg/budget/ -- cost tracking, budget enforcement
• CeremonyEvalContext.budget_consumed_fraction and budget_remaining

Dependencies

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