Add OpenCode agent support (#5)

Adds support for the OpenCode agent (https://opencode.ai), providing
users with another powerful AI code review option. Enhances #2

## Changes
- Add `opencode` agent implementation using non-interactive CLI mode
- Update fallback chain: codex → claude-code → gemini → copilot →
opencode
- Update tests, README, and CLI help text
- Follows same pattern as gemini/copilot PR (#3)

## Installation
```bash
npm install -g opencode-ai
```

## Testing
- [x] `go test ./...` passes
- [x] `go build ./...` succeeds
- [x] Follows established contribution patterns

## Notes
OpenCode is an open-source AI coding agent that supports multiple
backends, including local LLMs.

---------

Co-authored-by: Jonathan Sims <jonathan@simsventures.ai>
Co-authored-by: Claude <noreply@anthropic.com>

Author: 3 people

README.md

@@ -59,7 +59,7 @@ The range is inclusive of both endpoints. This is useful for reviewing a feature
 Per-repository `.roborev.toml`:
 
 ```toml
-agent = "claude-code"    # codex, claude-code, gemini, or copilot
+agent = "claude-code"    # codex, claude-code, gemini, copilot, or opencode
 review_context_count = 5
 
 # Project-specific review guidelines (multi-line string)
@@ -115,13 +115,14 @@ roborev supports multiple AI review agents:
 | `claude-code` | Anthropic Claude Code | `npm install -g @anthropic-ai/claude-code` |
 | `gemini` | Google Gemini | `npm install -g @google/gemini-cli` |
 | `copilot` | GitHub Copilot | `npm install -g @github/copilot` |
+| `opencode` | OpenCode | `npm install -g opencode-ai` |
 
 ### Automatic Fallback
 
 roborev automatically detects which agents are installed. If your preferred agent isn't available, it falls back in this order:
 
 ```
-codex → claude-code → gemini → copilot
+codex → claude-code → gemini → copilot → opencode
 ```
 
 If none are installed, the job fails with a helpful error message.
@@ -151,7 +152,7 @@ roborev enqueue HEAD --agent copilot
 1. `--agent` flag on enqueue command
 2. Per-repo `.roborev.toml`
 3. Global `~/.roborev/config.toml`
-4. Automatic detection (first available: codex → claude-code → gemini → copilot)
+4. Automatic detection (first available: codex → claude-code → gemini → copilot → opencode)
 
 ## Commands
 

cmd/roborev/main.go

@@ -32,7 +32,7 @@ func main() {
 	rootCmd := &cobra.Command{
 		Use:   "roborev",
 		Short: "Automatic code review for git commits",
-		Long:  "RoboRev automatically reviews git commits using AI agents (Codex, Claude Code, Gemini, Copilot)",
+		Long:  "RoboRev automatically reviews git commits using AI agents (Codex, Claude Code, Gemini, Copilot, OpenCode)",
 	}
 
 	rootCmd.PersistentFlags().StringVar(&serverAddr, "server", "http://127.0.0.1:7373", "daemon server address")
@@ -295,7 +295,7 @@ roborev enqueue --sha HEAD 2>/dev/null &
 		},
 	}
 
-	cmd.Flags().StringVar(&agent, "agent", "", "default agent (codex, claude-code, gemini, copilot)")
+	cmd.Flags().StringVar(&agent, "agent", "", "default agent (codex, claude-code, gemini, copilot, opencode)")
 
 	return cmd
 }
@@ -418,7 +418,7 @@ Examples:
 
 	cmd.Flags().StringVar(&repoPath, "repo", "", "path to git repository (default: current directory)")
 	cmd.Flags().StringVar(&sha, "sha", "HEAD", "commit SHA to review (used when no positional args)")
-	cmd.Flags().StringVar(&agent, "agent", "", "agent to use (codex, claude-code, gemini, copilot)")
+	cmd.Flags().StringVar(&agent, "agent", "", "agent to use (codex, claude-code, gemini, copilot, opencode)")
 
 	return cmd
 }

internal/agent/agent.go

@@ -73,8 +73,8 @@ func GetAvailable(preferred string) (Agent, error) {
 		return Get(preferred)
 	}
 
-	// Fallback order: codex, claude-code, gemini, copilot
-	fallbacks := []string{"codex", "claude-code", "gemini", "copilot"}
+	// Fallback order: codex, claude-code, gemini, copilot, opencode
+	fallbacks := []string{"codex", "claude-code", "gemini", "copilot", "opencode"}
 	for _, name := range fallbacks {
 		if name != preferred && IsAvailable(name) {
 			return Get(name)
@@ -90,7 +90,7 @@ func GetAvailable(preferred string) (Agent, error) {
 	}
 
 	if len(available) == 0 {
-		return nil, fmt.Errorf("no agents available (install one of: codex, claude-code, gemini, copilot)")
+		return nil, fmt.Errorf("no agents available (install one of: codex, claude-code, gemini, copilot, opencode)")
 	}
 
 	return Get(available[0])

internal/agent/agent_test.go

@@ -6,7 +6,7 @@ import (
 
 func TestAgentRegistry(t *testing.T) {
 	// Check that all agents are registered
-	agents := []string{"codex", "claude-code", "gemini", "copilot", "test"}
+	agents := []string{"codex", "claude-code", "gemini", "copilot", "opencode", "test"}
 	for _, name := range agents {
 		a, err := Get(name)
 		if err != nil {
@@ -26,16 +26,17 @@ func TestAgentRegistry(t *testing.T) {
 
 func TestAvailableAgents(t *testing.T) {
 	agents := Available()
-	// We have 5 agents: codex, claude-code, gemini, copilot, test
-	if len(agents) < 5 {
-		t.Errorf("Expected at least 5 agents, got %d: %v", len(agents), agents)
+	// We have 6 agents: codex, claude-code, gemini, copilot, opencode, test
+	if len(agents) < 6 {
+		t.Errorf("Expected at least 6 agents, got %d: %v", len(agents), agents)
 	}
 
 	expected := map[string]bool{
 		"codex":       false,
 		"claude-code": false,
 		"gemini":      false,
 		"copilot":     false,
+		"opencode":    false,
 		"test":        false,
 	}
 

internal/agent/opencode.go

@@ -0,0 +1,68 @@
+package agent
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+)
+
+// OpenCodeAgent runs code reviews using the OpenCode CLI
+type OpenCodeAgent struct {
+	Command string // The opencode command to run (default: "opencode")
+}
+
+// NewOpenCodeAgent creates a new OpenCode agent
+func NewOpenCodeAgent(command string) *OpenCodeAgent {
+	if command == "" {
+		command = "opencode"
+	}
+	return &OpenCodeAgent{Command: command}
+}
+
+func (a *OpenCodeAgent) Name() string {
+	return "opencode"
+}
+
+func (a *OpenCodeAgent) CommandName() string {
+	return a.Command
+}
+
+func (a *OpenCodeAgent) Review(ctx context.Context, repoPath, commitSHA, prompt string) (string, error) {
+	// OpenCode CLI supports a headless invocation via `opencode run [message..]`.
+	// We run it from the repo root so it can use project context, and pass the full
+	// roborev prompt as the message.
+	//
+	// Helpful reference:
+	//   opencode --help
+	//   opencode run --help
+	args := []string{"run", "--format", "default", prompt}
+
+	cmd := exec.CommandContext(ctx, a.Command, args...)
+	cmd.Dir = repoPath
+
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	if err := cmd.Run(); err != nil {
+		// opencode sometimes prints failures/usage to stdout; include both streams.
+		return "", fmt.Errorf(
+			"opencode failed: %w\nstdout: %s\nstderr: %s",
+			err,
+			stdout.String(),
+			stderr.String(),
+		)
+	}
+
+	output := stdout.String()
+	if len(output) == 0 {
+		return "No review output generated", nil
+	}
+
+	return output, nil
+}
+
+func init() {
+	Register(NewOpenCodeAgent(""))
+}