fix(cost): add dated model ID for Claude Sonnet 4.6

[colegottdank]

Summary

• Fixes $0 cost calculations for Claude Sonnet 4.6

Problem

PR #5579 added pricing for claude-sonnet-4-6 but the Anthropic API returns the dated version claude-sonnet-4-6-20260217. The cost lookup uses exact string matching, so it failed to find the model.

Changes

• Added claude-sonnet-4-6-20260217 to legacy cost lookup
• Added dated version to unified models mapping

Testing

All cost tests pass.

Priority

HIGH - Blocking customer from going live (ref: Arpit's Slack message)

🤖 Generated with Claude Code

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[claude]

Claude finished @colegottdank's task —— View job

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PR Review Complete ✅

Score: 8/10 - Good to merge, with minor suggestions for improvement

Analysis

This PR fixes a critical issue where Claude Sonnet 4.6 cost calculations were failing because the Anthropic API returns the dated version claude-sonnet-4-6-20260217 but the cost lookup only had claude-sonnet-4-6. The fix correctly adds the dated model ID to both the legacy cost system and unified model mapping.

Code Quality Review

✅ Strengths:

• Correct Fix: Addresses the exact problem described - API returning dated model ID while costs only defined for base model ID
• Consistent Implementation: Properly adds the dated model to both cost lookup systems
• Identical Cost Structure: Uses exact same pricing as the base model, which is appropriate since it's the same model
• Good Code Style: Follows existing patterns and formatting conventions
• Proper Documentation: Includes clear inline comments for cost values

⚠️ Areas for Improvement:

1. Missing Test Coverage: While the PR mentions "All cost tests pass", there don't appear to be specific tests for the dated model ID. Consider adding tests to ensure both claude-sonnet-4-6 and claude-sonnet-4-6-20260217 return the same costs.

2. Future Maintenance: This pattern suggests a potential need for a more systematic approach to handling dated model IDs. Consider whether a mapping or alias system could reduce duplication.

Technical Correctness

• ✅ Cost Values: Identical to base model - correct for same underlying model
• ✅ Model Mapping: Properly added to Anthropic provider with correct model string
• ✅ Structure Consistency: Follows existing patterns for model definitions
• ✅ No Breaking Changes: Additive changes only, maintains backward compatibility

Security & Performance

• ✅ No Security Issues: Changes are configuration-only with no executable code
• ✅ Performance Impact: Minimal - just additional lookup entries

Suggestions for Improvement

1. Add Unit Tests (packages/cost/__tests__/):

   describe('claude-sonnet-4-6 pricing', () => {
     it('should return same cost for base and dated model IDs', () => {
       // Test both claude-sonnet-4-6 and claude-sonnet-4-6-20260217
     });
   });

2. Consider Abstraction: For future dated models, consider implementing an alias system to reduce duplication while maintaining explicit control.

Summary

This is a well-implemented fix for a high-priority customer blocking issue. The changes are minimal, correct, and follow established patterns. The fix directly addresses the stated problem without introducing any risks or breaking changes.

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