feat: Add OpenAI spec compliance with developer role support

[vapi-tasker]

Summary

• Add developer role to message types for GPT-5.x and o-series models (HIGH priority)
• Create comprehensive type definitions in src/types/openai.ts
• Update ConversationMessageProps and ChatMessage interfaces to include developer role
• Add validation utilities: isValidRole, supportsDeveloperRole, validateRole
• Add deprecation notice for function role (recommend using tool instead)
• Export new types from main index for public API access
• Add Playwright tests for new functionality

Technical Details

New Types Added (src/types/openai.ts)

• MessageRole const object with all valid roles including developer
• OpenAIModel const object with GPT-5.x, o-series, and legacy models
• DEVELOPER_ROLE_MODELS array identifying models requiring developer role
• Utility functions: supportsDeveloperRole(), isValidRole(), isDeprecatedRole(), getReplacementRole(), validateRole(), createMessage()

Updated Interfaces

• ConversationMessageProps.role: Added 'developer' to union type
• MarkdownMessageProps.role: Updated to use ConversationMessageRole
• ChatMessage.role: Added 'developer' to union type

Testing

• Added tests/openai-types.spec.ts with Playwright tests covering:
  • MessageRole definitions
  • OpenAIModel definitions
  • Developer role detection for GPT-5.x and o-series models
  • Role validation utilities
  • Deprecation handling for function role

Backward Compatibility

• All existing roles (user, assistant, tool) continue to work unchanged
• The function role is still supported but will log a deprecation warning
• No breaking changes to existing APIs

Related

• Part of VAP-11729: Audit and update client SDKs against latest OpenAI spec
• Related PRs: server-sdk-typescript#35, client-sdk-web#151, client-sdk-python#22

Test plan

• Run npm run type-check - TypeScript compilation passes
• Run npm run lint - ESLint passes with no warnings
• Run npm run build - Production build succeeds
• Verify developer role can be used in ChatMessage
• Verify deprecation warning appears when using function role

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