# Multi-Provider Code Agent Interface

> **Status:** In Progress (Weeks 1-4 Complete)
> **Feature:** Unified interface supporting Claude Code and OpenCode providers

## Overview

This document describes the architecture for supporting multiple code agent providers (Claude Code, OpenCode) through a unified interface. The design enables provider switching at runtime without breaking existing functionality.

## Implementation Progress

| Phase | Status | Description |
|-------|--------|-------------|
| Week 1: Foundation | ✅ Complete | Domain models, port interface, registry |
| Week 2: Claude Code Adapter | ✅ Complete | kubectl exec wrapper, stream-json parser |
| Week 3: OpenCode Adapter | ✅ Complete | HTTP/SSE client, session management |
| Week 4: Service Integration | ✅ Complete | ProjectService integration, event streaming |
| Week 5: Polish | ⬜ Pending | Model selection API, health monitoring, metrics, docs |

## Architecture

### Current Flow

```
Handler → ProjectService → CodeAgent (port) → ClaudeCodeAdapter | OpenCodeAdapter
                                                     ↓                    ↓
                                              kubectl exec          HTTP API
                                              claude -p             opencode serve
```

### Fallback Support

When `CodeAgentRegistry` is not configured, the service falls back to the legacy `CommandExecutor` for backward compatibility.

## Domain Models (✅ Implemented)

### File: `internal/domain/code_agent.go`

```go
// AgentProvider identifies which code agent implementation to use
type AgentProvider string

const (
    AgentProviderClaudeCode AgentProvider = "claudecode"
    AgentProviderOpenCode   AgentProvider = "opencode"
)

// Validation and parsing
func (p AgentProvider) IsValid() bool
func (p AgentProvider) String() string
func ParseAgentProvider(s string) (AgentProvider, error)
func ValidAgentProviders() []AgentProvider

// AgentRequest contains parameters for executing a code agent command
type AgentRequest struct {
    Prompt       string
    ProjectID    ProjectID
    SessionID    string            // For continuation
    AllowedTools []string          // Tool restrictions
    Model        string            // Model override (OpenCode only)
    WorkingDir   string            // Defaults to /workspace
    Timeout      time.Duration     // Execution timeout
    Metadata     map[string]string // Provider-specific options
}

// AgentEventType categorizes events emitted during agent execution
type AgentEventType string

const (
    AgentEventOutput     AgentEventType = "output"
    AgentEventToolUse    AgentEventType = "tool_use"
    AgentEventToolResult AgentEventType = "tool_result"
    AgentEventThinking   AgentEventType = "thinking"
    AgentEventError      AgentEventType = "error"
    AgentEventComplete   AgentEventType = "complete"
)

// AgentEvent represents a single event during agent execution
type AgentEvent struct {
    Type      AgentEventType
    Timestamp time.Time
    Content   string
    Stream    string         // "stdout", "stderr", or empty
    ToolName  string         // For tool_use/tool_result events
    ToolInput map[string]any // Tool invocation arguments
    Metadata  map[string]any
}

// AgentEventHandler is a callback for receiving agent events
type AgentEventHandler func(event AgentEvent)

// AgentResult contains the outcome of agent execution
type AgentResult struct {
    SessionID   string           // For continuation
    ExitCode    int
    DurationMs  int64
    Error       error
    TokensUsed  *AgentTokenUsage // If available
    FinalOutput string
}

func (r *AgentResult) Success() bool // ExitCode == 0 && Error == nil

// AgentTokenUsage tracks token consumption
type AgentTokenUsage struct {
    InputTokens  int64
    OutputTokens int64
    TotalTokens  int64
}

// AgentCapabilities describes what a provider supports
type AgentCapabilities struct {
    Provider                    AgentProvider
    SupportsSessionContinuation bool
    SupportsModelSelection      bool
    SupportsToolControl         bool
    SupportedModels             []string
    DefaultModel                string
    MaxPromptLength             int
    SupportsStreaming           bool
}
```

### Project Extension

```go
// In domain/project.go
type Project struct {
    // ... existing fields ...
    AgentProvider AgentProvider // Which code agent to use
}

// New label for K8s discovery
const LabelAgentProvider = "rdev.orchard9.ai/agent-provider"
```

### Error Handling

```go
// In domain/errors.go
var ErrInvalidAgentProvider = errors.New("invalid agent provider")
```

## Port Interface (✅ Implemented)

### File: `internal/port/code_agent.go`

```go
// CodeAgent defines operations for executing AI coding agent commands
type CodeAgent interface {
    // Name returns a human-readable name for this agent
    Name() string

    // Provider returns the agent provider identifier
    Provider() domain.AgentProvider

    // Execute runs an agent command and streams events to the handler
    Execute(ctx context.Context, req *domain.AgentRequest, handler domain.AgentEventHandler) (*domain.AgentResult, error)

    // Cancel attempts to cancel a running agent session
    Cancel(ctx context.Context, sessionID string) error

    // Capabilities returns what this agent supports
    Capabilities() domain.AgentCapabilities

    // Available returns true if the agent is ready to accept requests
    Available(ctx context.Context) bool
}

// CodeAgentRegistry manages registered code agent implementations
type CodeAgentRegistry interface {
    // Register adds an agent for a provider (overwrites existing)
    Register(agent CodeAgent)

    // Get returns the agent for a specific provider (nil if not found)
    Get(provider domain.AgentProvider) CodeAgent

    // Default returns the default agent (nil if empty)
    Default() CodeAgent

    // SetDefault sets the default provider (error if not registered)
    SetDefault(provider domain.AgentProvider) error

    // Available returns all registered providers
    Available() []domain.AgentProvider

    // AvailableAgents returns agents that are currently available
    AvailableAgents(ctx context.Context) []CodeAgent
}
```

## Provider Registry (✅ Implemented)

### File: `internal/adapter/codeagent/registry.go`

```go
// Registry implements port.CodeAgentRegistry with thread-safe agent management
type Registry struct {
    mu       sync.RWMutex
    agents   map[domain.AgentProvider]port.CodeAgent
    defProv  domain.AgentProvider
    hasAgent bool
}

func NewRegistry() *Registry

// Additional methods beyond interface
func (r *Registry) DefaultProvider() domain.AgentProvider
func (r *Registry) Count() int
```

**Thread Safety:**
- `sync.RWMutex` for concurrent access
- Read locks for: `Get`, `Default`, `Available`, `AvailableAgents`, `DefaultProvider`, `Count`
- Write locks for: `Register`, `SetDefault`
- First registered agent becomes default automatically

**Test Coverage:**
- Register/Get operations
- Default selection (first registered)
- SetDefault (success and failure)
- Available providers listing
- AvailableAgents filtering
- Concurrent access (race-tested)
- Re-registration overwrites

## Claude Code Adapter (✅ Implemented)

### Package: `internal/adapter/codeagent/claudecode/`

**Files:**
- `adapter.go` - CodeAgent implementation wrapping kubectl exec
- `parser.go` - Stream-JSON NDJSON parser for Claude Code output
- `adapter_test.go` - Comprehensive test coverage
- `parser_test.go` - Parser unit tests

**Key Features:**
- Wraps `kubectl exec` for pod access
- Uses `--output-format stream-json` for structured NDJSON output
- Supports `--resume <session_id>` for conversation continuation
- Maps `AllowedTools` to `--allowedTools` flag
- Uses `--dangerously-skip-permissions` for non-interactive mode

**Command Construction:**
```go
func (a *Adapter) buildCommandArgs(namespace, podName string, req *domain.AgentRequest) []string {
    args := []string{
        "exec", "-n", namespace, podName, "--",
        "claude", "-p", "--output-format", "stream-json", "--dangerously-skip-permissions",
    }
    if req.SessionID != "" {
        args = append(args, "--resume", req.SessionID)
    }
    for _, tool := range req.AllowedTools {
        args = append(args, "--allowedTools", tool)
    }
    if req.WorkingDir != "" && req.WorkingDir != "/workspace" {
        args = append(args, "--add-dir", req.WorkingDir)
    }
    args = append(args, req.Prompt)
    return args
}
```

**Stream JSON Message Types:**
| Type | Description | Mapped Event |
|------|-------------|--------------|
| `init` | Session started | `AgentEventOutput` |
| `message` | Text output from assistant | `AgentEventOutput` |
| `tool_use` | Tool invocation | `AgentEventToolUse` |
| `tool_result` | Tool response | `AgentEventToolResult` |
| `result` | Execution complete | `AgentEventComplete` |

**Capabilities:**
```go
func (a *Adapter) Capabilities() domain.AgentCapabilities {
    return domain.AgentCapabilities{
        Provider:                    domain.AgentProviderClaudeCode,
        SupportsSessionContinuation: true,
        SupportsModelSelection:      false, // Claude Code only uses Claude
        SupportsToolControl:         true,
        SupportedModels:             []string{"claude-sonnet-4-20250514", "claude-opus-4-20250514"},
        DefaultModel:                "claude-sonnet-4-20250514",
        MaxPromptLength:             0, // Unlimited
        SupportsStreaming:           true,
    }
}
```

## OpenCode Adapter (✅ Implemented)

### Package: `internal/adapter/codeagent/opencode/`

**Files:**
- `adapter.go` - CodeAgent implementation using HTTP/SSE
- `client.go` - HTTP client with SSE subscription support
- `adapter_test.go` - Mock server tests for all operations

**HTTP Client API:**
```go
type Client struct {
    baseURL    string
    httpClient *http.Client
    username   string
    password   string
}

// Health check
func (c *Client) Health(ctx context.Context) (*HealthResponse, error)

// Session management
func (c *Client) CreateSession(ctx context.Context, req *CreateSessionRequest) (*Session, error)
func (c *Client) GetSession(ctx context.Context, sessionID string) (*Session, error)
func (c *Client) AbortSession(ctx context.Context, sessionID string) error

// Message sending
func (c *Client) SendMessage(ctx context.Context, sessionID string, req *SendMessageRequest) (*SendMessageResponse, error)
func (c *Client) SendPromptAsync(ctx context.Context, sessionID string, req *SendMessageRequest) error

// SSE streaming
func (c *Client) SubscribeEvents(ctx context.Context) (<-chan SSEEvent, error)
```

**SSE Event Mapping:**
| SSE Event | Description | Mapped Event |
|-----------|-------------|--------------|
| `server.connected` | Connected to server | `AgentEventOutput` |
| `message.created` | New message | `AgentEventOutput` |
| `message.updated` | Message updated | `AgentEventOutput` |
| `tool.started` | Tool execution started | `AgentEventToolUse` |
| `tool.completed` | Tool execution done | `AgentEventToolResult` |
| `session.completed` | Session finished | `AgentEventComplete` |
| `error` | Error occurred | `AgentEventError` |

**Capabilities:**
```go
func (a *Adapter) Capabilities() domain.AgentCapabilities {
    return domain.AgentCapabilities{
        Provider:                    domain.AgentProviderOpenCode,
        SupportsSessionContinuation: true,
        SupportsModelSelection:      true, // OpenCode supports multiple providers
        SupportsToolControl:         true,
        SupportedModels: []string{
            "claude-sonnet-4-20250514",
            "claude-opus-4-20250514",
            "gpt-4o",
            "gpt-4-turbo",
            "gemini-pro",
        },
        DefaultModel:      "claude-sonnet-4-20250514",
        MaxPromptLength:   0, // Unlimited
        SupportsStreaming: true,
    }
}
```

**Authentication:**
- Basic auth support via `username` and `password` config
- Default username: `opencode`

## Service Integration (✅ Implemented)

### Files Modified/Created

| File | Description |
|------|-------------|
| `project_service.go` | Core service with agent registry support |
| `project_service_agent.go` | Agent execution and resolution methods |
| `project_service_commands.go` | Shell/Git command execution (extracted) |
| `project_service_queue.go` | Queue operations (extracted) |

### ProjectService Changes

**New Fields:**
```go
type ProjectService struct {
    // ... existing fields ...
    agentRegistry port.CodeAgentRegistry // Optional code agent registry
}

func (s *ProjectService) WithCodeAgentRegistry(registry port.CodeAgentRegistry) *ProjectService
```

**Updated Request/Response:**
```go
type ExecuteClaudeRequest struct {
    ProjectID    domain.ProjectID
    Prompt       string
    StreamID     string
    SessionID    string            // Optional: resume a previous session
    Model        string            // Optional: model override (OpenCode only)
    AllowedTools []string          // Optional: restrict tool access
    Audit        *AuditContext
}

type ExecuteClaudeResult struct {
    CommandID     domain.CommandID
    StreamURL     string
    SessionID     string              // Session ID for continuation
    AgentProvider domain.AgentProvider // Which provider handled the request
}
```

**Agent Resolution:**
```go
// resolveAgent returns the appropriate CodeAgent for a project.
// Returns nil if no agent registry is configured or no agent is available.
func (s *ProjectService) resolveAgent(project *domain.Project) port.CodeAgent {
    if s.agentRegistry == nil {
        return nil
    }

    // Try project-specific agent first
    if project.AgentProvider != "" {
        if agent := s.agentRegistry.Get(project.AgentProvider); agent != nil {
            return agent
        }
    }

    // Fall back to default
    return s.agentRegistry.Default()
}
```

**Event Streaming:**

Agent events are converted to SSE stream events:

| Agent Event | Stream Event | Data |
|-------------|--------------|------|
| `AgentEventOutput` | `output` | `{line, stream}` |
| `AgentEventToolUse` | `tool_use` | `{tool, input}` |
| `AgentEventToolResult` | `tool_result` | `{output}` |
| `AgentEventError` | `error` | `{error}` |
| `AgentEventComplete` | `agent_complete` | metadata |
| (final) | `complete` | `{exit_code, duration_ms, session_id, provider}` |

**Additional Service Methods:**
```go
// Get capabilities for a specific provider
func (s *ProjectService) GetAgentCapabilities(provider domain.AgentProvider) *domain.AgentCapabilities

// List all available providers
func (s *ProjectService) ListAvailableAgents() []domain.AgentProvider

// Get/set default agent
func (s *ProjectService) GetDefaultAgent() domain.AgentProvider
func (s *ProjectService) SetDefaultAgent(provider domain.AgentProvider) error
```

## API Changes (⬜ Pending - Week 5)

### Project Response

```json
{
  "id": "proj-123",
  "name": "my-project",
  "agent_provider": "claudecode",
  "agent_capabilities": {
    "supports_session_continuation": true,
    "supports_model_selection": false
  }
}
```

### Update Provider

```http
PATCH /projects/{id}
Content-Type: application/json

{
  "agent_provider": "opencode"
}
```

### Execute with Model (OpenCode only)

```http
POST /projects/{id}/claude
Content-Type: application/json

{
  "prompt": "Fix the bug in main.go",
  "model": "gpt-4o",
  "session_id": "prev-session-123"
}
```

## Configuration

### Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| `CODE_AGENT_DEFAULT` | `claudecode` | Default provider for new projects |
| `OPENCODE_ENABLED` | `false` | Enable OpenCode adapter |
| `OPENCODE_URL` | `http://127.0.0.1:4096` | OpenCode server URL |
| `OPENCODE_USERNAME` | `opencode` | OpenCode basic auth username |
| `OPENCODE_PASSWORD` | (none) | OpenCode basic auth password |

### Project-Level Override

Projects can specify their preferred provider in the database. On provider switch:
1. Active session is cleared (no cross-provider continuation)
2. New provider is validated as available
3. Next command uses new provider

## File Structure

```
internal/
├── domain/
│   ├── code_agent.go           ✅ AgentProvider, AgentRequest, AgentEvent, etc.
│   ├── code_agent_test.go      ✅ Domain model tests
│   ├── project.go              ✅ Added AgentProvider field
│   └── errors.go               ✅ Added ErrInvalidAgentProvider
├── port/
│   └── code_agent.go           ✅ CodeAgent, CodeAgentRegistry interfaces
├── adapter/
│   └── codeagent/
│       ├── registry.go         ✅ Provider registry implementation
│       ├── registry_test.go    ✅ Registry tests (incl. concurrent access)
│       ├── claudecode/         ✅ Week 2
│       │   ├── adapter.go      ✅ CodeAgent implementation
│       │   ├── parser.go       ✅ Stream-JSON NDJSON parser
│       │   ├── adapter_test.go ✅ Adapter tests
│       │   └── parser_test.go  ✅ Parser tests
│       └── opencode/           ✅ Week 3
│           ├── adapter.go      ✅ CodeAgent implementation
│           ├── client.go       ✅ HTTP/SSE client
│           └── adapter_test.go ✅ Mock server tests
├── service/
│   ├── project_service.go       ✅ Week 4: Agent registry integration
│   ├── project_service_agent.go ✅ Week 4: Agent execution methods
│   ├── project_service_commands.go ✅ Extracted shell/git commands
│   └── project_service_queue.go ✅ Extracted queue operations
└── worker/
    └── queue_processor.go       ⬜ Week 5: Use CodeAgent for queue
```

## Observability (⬜ Pending - Week 5)

### Metrics

| Metric | Labels | Description |
|--------|--------|-------------|
| `code_agent_requests_total` | provider, project, status | Total requests |
| `code_agent_duration_seconds` | provider, project | Execution duration |
| `code_agent_events_total` | provider, event_type | Streaming events |

### Health Check

```http
GET /health

{
  "status": "healthy",
  "agents": {
    "claudecode": "available",
    "opencode": "unavailable"
  }
}
```

## Risks and Mitigations

| Risk | Impact | Mitigation |
|------|--------|------------|
| OpenCode API changes | Adapter breaks | Pin to specific version, add API versioning |
| Latency difference (subprocess vs HTTP) | User experience varies | Monitor p99 latency, document tradeoffs |
| Session state incompatibility | Can't resume across providers | Clear session on provider switch |
| Container image size increase | Slower deployments | OpenCode sidecar optional, not in base image |

## Design Decisions

1. **Event callback pattern** - Matches existing `OutputHandler`, enables streaming
2. **Registry pattern** - Allows runtime switching, extensible for more providers
3. **OpenCode as sidecar** - Keeps Claude Code as proven default, OpenCode opt-in
4. **Session per provider** - No cross-provider session sharing to avoid state corruption
5. **First-registered default** - Registry automatically uses first agent as default
6. **Backward compatibility** - Falls back to legacy executor when no registry configured
7. **File splitting** - Service files split to comply with 500-line limit