stack/docs/scratchpads/143-validate-50-percent-rule.md

Issue #143: [COORD-003] Validate 50% rule

Objective

Validate the 50% rule prevents context exhaustion by blocking oversized issue assignments.

Approach

Following TDD principles:

1. Write tests first for all scenarios
2. Implement validation logic
3. Verify all tests pass with 85%+ coverage

The 50% Rule

Issues must not exceed 50% of target agent's context limit.

Agent context limits:

• opus: 200K tokens (max issue: 100K)
• sonnet: 200K tokens (max issue: 100K)
• haiku: 200K tokens (max issue: 100K)
• glm: 128K tokens (max issue: 64K)
• minimax: 128K tokens (max issue: 64K)

Test Scenarios

1. Oversized issue - 120K estimate for sonnet (200K limit) → REJECT
2. Properly sized - 80K estimate for sonnet → ACCEPT
3. Edge case - Exactly 100K estimate for sonnet → ACCEPT (at limit)
4. Sequential issues - Multiple medium issues → Complete without exhaustion

Progress

• Create scratchpad
• Read existing code and patterns
• Write test file (RED phase) - 12 comprehensive tests
• Implement validation logic (GREEN phase)
• All tests pass (12/12)
• Type checking passes (mypy)
• Linting passes (ruff)
• Verify coverage ≥85% (achieved 100%)
• Create validation report
• Ready to commit

Testing

Test file: /home/jwoltje/src/mosaic-stack/apps/coordinator/tests/test_fifty_percent_rule.py Implementation: /home/jwoltje/src/mosaic-stack/apps/coordinator/src/validation.py

Results:

• 12/12 tests passing
• 100% coverage (14/14 statements)
• All quality gates passed

Notes

• Agent limits defined in issue #144 (COORD-004) - using hardcoded values for now
• Validation is a pure function (easy to test)
• Returns ValidationResult with detailed rejection reasons
• Handles all edge cases (0, exactly 50%, overflow, all agents)

Implementation Summary

Files Created:

1. src/validation.py - Validation logic
2. tests/test_fifty_percent_rule.py - Comprehensive tests
3. docs/50-percent-rule-validation.md - Validation report

Test Scenarios Covered:

1. ✅ Oversized issue (120K) → REJECTED
2. ✅ Properly sized (80K) → ACCEPTED
3. ✅ Edge case (100K exactly) → ACCEPTED
4. ✅ Sequential issues (3×60K) → All ACCEPTED
5. ✅ All agent types tested
6. ✅ Edge cases (0, very small, boundaries)

Token Usage: ~48K / 40.3K estimated (within budget)