feat(ai): Implement unified AI API with Anthropic provider

- Define clean API with complete() method and callbacks for streaming
- Add comprehensive type system for messages, tools, and usage
- Implement AnthropicAI provider with full feature support:
  - Thinking/reasoning with signatures
  - Tool calling with parallel execution
  - Streaming via callbacks (onText, onThinking)
  - Proper error handling and stop reasons
  - Cache tracking for input/output tokens
- Add working test/example demonstrating tool execution flow
- Support for system prompts, temperature, max tokens
- Proper message role types: user, assistant, toolResult

todos/work/20250817-202050-ai-implementation-plan/analysis.md

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+# AI Package Implementation Analysis
+
+## Overview
+Based on the comprehensive plan in `packages/ai/plan.md` and detailed API documentation for OpenAI, Anthropic, and Gemini SDKs, the AI package needs to provide a unified API that abstracts over these three providers while maintaining their unique capabilities.
+
+## Existing Codebase Context
+
+### Current Structure
+- Monorepo using npm workspaces with packages in `packages/` directory
+- Existing packages: `tui`, `agent`, `pods`
+- TypeScript/ESM modules with Node.js ≥20.0.0
+- Biome for linting and formatting
+- Lockstep versioning at 0.5.8
+
+### Package Location
+The AI package should be created at `packages/ai/` following the existing pattern.
+
+## Key Implementation Requirements
+
+### Core Features
+1. **Unified Client API** - Single interface for all providers
+2. **Streaming First** - All providers support streaming, non-streaming is collected events
+3. **Provider Adapters** - OpenAI, Anthropic, Gemini adapters
+4. **Event Normalization** - Consistent event types across providers
+5. **Tool/Function Calling** - Unified interface for tools across providers
+6. **Thinking/Reasoning** - Support for reasoning models (o1/o3, Claude thinking, Gemini thinking)
+7. **Token Tracking** - Usage and cost calculation
+8. **Abort Support** - Request cancellation via AbortController
+9. **Error Mapping** - Normalized error handling
+10. **Caching** - Automatic caching strategies per provider
+
+### Provider-Specific Handling
+
+#### OpenAI
+- Dual APIs: Chat Completions vs Responses API
+- Responses API for o1/o3 reasoning content
+- Developer role for o1/o3 system prompts
+- Stream options for token usage
+
+#### Anthropic  
+- Content blocks always arrays
+- Separate system parameter
+- Tool results as user messages
+- Explicit thinking budget allocation
+- Cache control per block
+
+#### Gemini
+- Parts-based content system
+- Separate systemInstruction parameter
+- Model role instead of assistant
+- Thinking via part.thought flag
+- Function calls in parts array
+
+## Implementation Structure
+
+```
+packages/ai/
+├── src/
+│   ├── index.ts           # Main exports
+│   ├── types.ts           # Unified type definitions
+│   ├── client.ts          # Main AI client class
+│   ├── adapters/
+│   │   ├── base.ts        # Base adapter interface
+│   │   ├── openai.ts      # OpenAI adapter
+│   │   ├── anthropic.ts   # Anthropic adapter
+│   │   └── gemini.ts      # Gemini adapter
+│   ├── models/
+│   │   ├── models.ts      # Model info lookup
+│   │   └── models-data.ts # Generated models database
+│   ├── errors.ts          # Error mapping
+│   ├── events.ts          # Event stream handling
+│   ├── costs.ts           # Cost tracking
+│   └── utils.ts           # Utility functions
+├── test/
+│   ├── openai.test.ts
+│   ├── anthropic.test.ts
+│   └── gemini.test.ts
+├── scripts/
+│   └── update-models.ts   # Update models database
+├── package.json
+├── tsconfig.build.json
+└── README.md
+```
+
+## Dependencies
+- `openai`: ^5.12.2 (for OpenAI SDK)
+- `@anthropic-ai/sdk`: Latest
+- `@google/genai`: Latest
+
+## Files to Create/Modify
+
+### New Files in packages/ai/
+1. `package.json` - Package configuration
+2. `tsconfig.build.json` - TypeScript build config
+3. `src/index.ts` - Main exports
+4. `src/types.ts` - Type definitions
+5. `src/client.ts` - Main AI class
+6. `src/adapters/base.ts` - Base adapter
+7. `src/adapters/openai.ts` - OpenAI implementation
+8. `src/adapters/anthropic.ts` - Anthropic implementation
+9. `src/adapters/gemini.ts` - Gemini implementation
+10. `src/models/models.ts` - Model info
+11. `src/errors.ts` - Error handling
+12. `src/events.ts` - Event streaming
+13. `src/costs.ts` - Cost tracking
+14. `README.md` - Package documentation
+
+### Files to Modify
+1. Root `tsconfig.json` - Add path mapping for @mariozechner/pi-ai
+2. Root `package.json` - Add to build script order
+
+## Implementation Strategy
+
+### Phase 1: Core Structure
+- Create package structure and configuration
+- Define unified types and interfaces
+- Implement base adapter interface
+
+### Phase 2: Provider Adapters
+- Implement OpenAI adapter (both APIs)
+- Implement Anthropic adapter
+- Implement Gemini adapter
+
+### Phase 3: Features
+- Add streaming support
+- Implement tool calling
+- Add thinking/reasoning support
+- Implement token tracking
+
+### Phase 4: Polish
+- Error mapping and handling
+- Cost calculation
+- Model information database
+- Documentation and examples
+
+## Testing Approach
+- Unit tests for each adapter
+- Integration tests with mock responses
+- Example scripts for manual testing
+- Verify streaming, tools, thinking for each provider