feat(schemas): add discriminated union to QualityMetricsSchema

[EdwardIrby]

Summary

• Adds type: z.literal('run') discriminator to QualityMetricsSchema and type: z.literal('trial') to TrialsQualityMetricsSchema
• Aligns quality metrics with the existing discriminated union pattern used by ReliabilityMetricsSchema / TrialsReliabilityMetricsSchema
• Eliminates the need for custom type guards — consumers can now narrow with metrics.type === 'run' or metrics.type === 'trial'

Closes #50

Test plan

• bun run check passes (type-check, lint, format)
• bun test passes (563 tests, 0 failures)
• New assertions verify type: 'run' in compare-statistical.spec.ts
• New assertions verify type: 'trial' in compare-trials.spec.ts
• Confirmed discriminator pattern matches ReliabilityMetricsSchema

🤖 Generated with Claude Code

[claude]

Review Summary

✅ Approved - This is a clean, well-tested enhancement that improves type safety and consistency.

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Code Quality

Strengths:

• ✅ Perfectly aligns with existing pattern in ReliabilityMetricsSchema / TrialsReliabilityMetricsSchema
• ✅ Adds discriminator fields to both QualityMetricsSchema (type: 'run') and TrialsQualityMetricsSchema (type: 'trial')
• ✅ Comprehensive test coverage with new assertions in both test files
• ✅ TSDoc comments appropriately updated
• ✅ Follows core conventions: proper TypeScript, clean diff, minimal changes

Implementation correctness:

• The schemas remain separate (not merged into z.discriminatedUnion) because they're used in different contexts:
  • QualityMetricsSchema → ComparisonReport.quality (schemas.ts:812)
  • TrialsQualityMetricsSchema → TrialsComparisonReport.quality (schemas.ts:1056)
• This matches the reliability metrics pattern exactly

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Test Coverage

✅ Excellent coverage

• New assertions in compare-statistical.spec.ts:809-812 verify type: 'run'
• New assertion in compare-trials.spec.ts:480 verifies type: 'trial'
• All 563 tests passing per PR description
• Tests verify the discriminator at the output boundary (after computation)

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Best Practices Compliance

Checked against .agents/rules/:

Rule	Status	Notes
core.md	✅	Uses type (not interface), proper TSDoc, no violations
testing.md	✅	Uses test(), clear assertions, both code paths tested
accuracy.md	✅	Implementation verified against existing ReliabilityMetrics pattern
modules.md	✅	No new files, clean edits to existing modules
documentation.md	✅	TSDoc comments properly describe discriminators

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Potential Improvements (Optional)

Consider for future (not blocking):

1. Type narrowing helper - While the discriminator enables manual narrowing, consumers might benefit from a helper:

   export const isRunQuality = (m: QualityMetrics | TrialsQualityMetrics): m is QualityMetrics => m.type === 'run'
   export const isTrialQuality = (m: QualityMetrics | TrialsQualityMetrics): m is TrialsQualityMetrics => m.type === 'trial'

   However, this assumes consumers receive both types in a union, which may not be the common case.

2. Migration guide - If this is consumed by external projects, a changelog entry documenting the new required field would help downstream consumers update their parsers.

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Security & Performance

• ✅ No security concerns (pure schema changes)
• ✅ No performance impact (single field addition)
• ✅ No breaking API changes (additive only)

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Final Verdict

This PR is ready to merge. It successfully addresses issue #50 by adding type discriminators to quality metrics schemas, making them consistent with reliability metrics and improving TypeScript developer experience.

The implementation is minimal, well-tested, and follows all repository conventions.

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Files reviewed:

• src/schemas/schemas.ts - Schema definitions
• src/pipeline/compare.ts - Run quality metrics computation
• src/pipeline/compare-trials.ts - Trial quality metrics computation
• src/pipeline/tests/compare-statistical.spec.ts - Run metrics tests
• src/pipeline/tests/compare-trials.spec.ts - Trial metrics tests

🤖 Review performed by Claude Sonnet 4.5

[claude]

PR Review: Add discriminated union to QualityMetricsSchema

Summary

This PR adds type discriminators (type: 'run' and type: 'trial') to quality metrics schemas, aligning them with the existing reliability metrics pattern. The implementation is clean, well-tested, and follows repository conventions.

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✅ Code Quality

Strengths:

• Perfect consistency with existing ReliabilityMetricsSchema / TrialsReliabilityMetricsSchema pattern (schemas.ts:694-696, 882-884)
• Minimal, focused changes - only touches necessary files
• Proper TSDoc comments for new discriminator fields
• Follows all core conventions (type over interface, arrow functions, PascalCase)

Implementation:

• QualityMetricsSchema gets type: z.literal('run') (schemas.ts:794-795)
• TrialsQualityMetricsSchema gets type: z.literal('trial') (schemas.ts:947-948)
• Discriminators added at computation sites:
  • compare.ts:368 - run quality metrics
  • compare-trials.ts:265 - trial quality metrics

---

✅ Test Coverage

Excellent coverage:

• New assertions in compare-statistical.spec.ts:809-812 verify type: 'run'
• New assertion in compare-trials.spec.ts:482 verifies type: 'trial'
• Tests verify discriminators at output boundaries (after computation)
• All 563 tests passing (per PR description)

Pattern validation:
Both test files now verify discriminators consistently with existing reliability metrics tests.

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✅ Architecture & Design

Why separate schemas (not z.discriminatedUnion)?
The implementation correctly keeps schemas separate because they're used in different contexts:

• QualityMetricsSchema → ComparisonReport.quality (schemas.ts:812)
• TrialsQualityMetricsSchema → TrialsComparisonReport.quality (schemas.ts:1056)

This matches the reliability metrics pattern exactly - schemas are structurally similar but serve different comparison types.

Type narrowing:
Consumers can now narrow with metrics.type === 'run' or metrics.type === 'trial', eliminating need for custom type guards.

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🔍 Additional Changes Review

Rules consolidation (AGENTS.md):

• Deleted individual .agents/rules/*.md files
• Consolidated all rules into AGENTS.md between <!-- PLAITED-RULES-START/END --> markers
• Removed symlinks (.claude/rules, .cursor/rules)
• This aligns with the scaffold-rules skill update (SKILL.md:273-302)

Rationale: Rules are now inline in AGENTS.md for better discoverability and single-source-of-truth maintenance.

Dependency updates:

• @biomejs/biome: 2.3.12 → 2.3.14
• @types/bun: 1.3.6 → 1.3.9
• @plaited/development-skills: 0.7.0 → 0.8.0

These are minor version bumps (patch/minor) - safe to include.

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🛡️ Security & Performance

• ✅ No security concerns (pure schema changes)
• ✅ No performance impact (single field addition)
• ✅ Additive change - no breaking API changes

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📋 Best Practices Compliance

Checked against .agents/rules/ (now in AGENTS.md):

Rule	Status	Notes
Bun APIs	✅	No Bun API changes
Core conventions	✅	Uses type, proper TSDoc, correct naming
Testing	✅	Uses test(), clear assertions, both paths tested
Modules	✅	No new files, clean edits to existing modules
Documentation	✅	TSDoc properly describes discriminators
Workflow	✅	Conventional commit format, proper PR structure

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💡 Optional Future Enhancements (Not blocking)

1. Type narrowing helpers - If consumers receive both types in a union context:

   export const isRunQuality = (m: QualityMetrics | TrialsQualityMetrics): m is QualityMetrics => 
     m.type === 'run'

   However, this may not be a common use case based on current architecture.

2. Migration note - If this library has external consumers, consider documenting the new required field in CHANGELOG.

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✅ Final Verdict

LGTM - Ready to merge

This PR successfully addresses issue #50 by:

• Adding type discriminators to quality metrics schemas
• Maintaining consistency with existing reliability metrics pattern
• Improving TypeScript developer experience
• Including comprehensive test coverage
• Following all repository conventions

The implementation is minimal, well-tested, and production-ready.

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Files reviewed:

• src/schemas/schemas.ts - Schema definitions ✅
• src/pipeline/compare.ts - Run quality metrics computation ✅
• src/pipeline/compare-trials.ts - Trial quality metrics computation ✅
• src/pipeline/tests/compare-statistical.spec.ts - Run metrics tests ✅
• src/pipeline/tests/compare-trials.spec.ts - Trial metrics tests ✅
• AGENTS.md - Rules consolidation ✅
• package.json / bun.lock - Dependency updates ✅

🤖 Review performed by Claude Sonnet 4.5