Add gemini-cli, copilot CLI support (#3)

* Add Gemini CLI and GitHub Copilot CLI agents

- Add gemini agent using `gemini -p` for non-interactive reviews
- Add copilot agent using `copilot --prompt` for non-interactive reviews
- Update fallback order to include new agents
- Update tests to verify all 5 agents are registered

Install with:
  npm install -g @google/gemini-cli
  npm install -g @github/copilot

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update README with expanded agent support

- Add table showing all 4 agents with install commands
- Document fallback order: codex → claude-code → gemini → copilot
- Improve "Setting the Default Agent" section with all config options
- Update config example to list all agent options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update error message to list all supported agents

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update CLI help text to list all supported agents

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: wesm

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"    # or "codex"
+agent = "claude-code"    # codex, claude-code, gemini, or copilot
 review_context_count = 5
 
 # Project-specific review guidelines (multi-line string)
@@ -109,37 +109,49 @@ The daemon starts automatically when needed and handles port conflicts by findin
 
 roborev supports multiple AI review agents:
 
-- `codex` - OpenAI Codex CLI
-- `claude-code` - Anthropic Claude Code CLI
+| Agent | CLI | Install |
+|-------|-----|---------|
+| `codex` | OpenAI Codex | `npm install -g @openai/codex` |
+| `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` |
 
 ### Automatic Fallback
 
-roborev automatically detects which agents are installed and falls back gracefully:
+roborev automatically detects which agents are installed. If your preferred agent isn't available, it falls back in this order:
 
-- If `codex` is requested but not installed, roborev uses `claude` instead
-- If `claude-code` is requested but not installed, roborev uses `codex` instead
-- If neither is installed, the job fails with a helpful error message
+```
+codex → claude-code → gemini → copilot
+```
 
-### Explicit Agent Selection
+If none are installed, the job fails with a helpful error message.
 
-To use a specific agent for a repository, create `.roborev.toml` in the repo root:
+### Setting the Default Agent
+
+**Per-repository** - create `.roborev.toml` in the repo root:
 
 ```toml
-agent = "claude-code"
+agent = "gemini"
 ```
 
-Or set a global default in `~/.roborev/config.toml`:
+**Global default** - create or edit `~/.roborev/config.toml`:
 
 ```toml
 default_agent = "claude-code"
 ```
 
+**Per-command** - use the `--agent` flag:
+
+```bash
+roborev enqueue HEAD --agent copilot
+```
+
 ### Selection Priority
 
 1. `--agent` flag on enqueue command
 2. Per-repo `.roborev.toml`
 3. Global `~/.roborev/config.toml`
-4. Automatic detection (uses first available: codex, claude-code)
+4. Automatic detection (first available: codex → claude-code → gemini → copilot)
 
 ## 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)",
+		Long:  "RoboRev automatically reviews git commits using AI agents (Codex, Claude Code, Gemini, Copilot)",
 	}
 
 	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)")
+	cmd.Flags().StringVar(&agent, "agent", "", "default agent (codex, claude-code, gemini, copilot)")
 
 	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)")
+	cmd.Flags().StringVar(&agent, "agent", "", "agent to use (codex, claude-code, gemini, copilot)")
 
 	return cmd
 }

internal/agent/agent.go

@@ -73,8 +73,8 @@ func GetAvailable(preferred string) (Agent, error) {
 		return Get(preferred)
 	}
 
-	// Fallback order: codex, claude-code
-	fallbacks := []string{"codex", "claude-code"}
+	// Fallback order: codex, claude-code, gemini, copilot
+	fallbacks := []string{"codex", "claude-code", "gemini", "copilot"}
 	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 codex or claude)")
+		return nil, fmt.Errorf("no agents available (install one of: codex, claude-code, gemini, copilot)")
 	}
 
 	return Get(available[0])

internal/agent/agent_test.go

@@ -5,51 +5,49 @@ import (
 )
 
 func TestAgentRegistry(t *testing.T) {
-	// Check that default agents are registered
-	codex, err := Get("codex")
-	if err != nil {
-		t.Fatalf("Failed to get codex agent: %v", err)
-	}
-	if codex.Name() != "codex" {
-		t.Errorf("Expected name 'codex', got '%s'", codex.Name())
-	}
-
-	claude, err := Get("claude-code")
-	if err != nil {
-		t.Fatalf("Failed to get claude-code agent: %v", err)
-	}
-	if claude.Name() != "claude-code" {
-		t.Errorf("Expected name 'claude-code', got '%s'", claude.Name())
+	// Check that all agents are registered
+	agents := []string{"codex", "claude-code", "gemini", "copilot", "test"}
+	for _, name := range agents {
+		a, err := Get(name)
+		if err != nil {
+			t.Fatalf("Failed to get %s agent: %v", name, err)
+		}
+		if a.Name() != name {
+			t.Errorf("Expected name '%s', got '%s'", name, a.Name())
+		}
 	}
 
 	// Check unknown agent
-	_, err = Get("unknown-agent")
+	_, err := Get("unknown-agent")
 	if err == nil {
 		t.Error("Expected error for unknown agent")
 	}
 }
 
 func TestAvailableAgents(t *testing.T) {
 	agents := Available()
-	if len(agents) < 2 {
-		t.Errorf("Expected at least 2 agents, got %d", len(agents))
+	// 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)
+	}
+
+	expected := map[string]bool{
+		"codex":       false,
+		"claude-code": false,
+		"gemini":      false,
+		"copilot":     false,
+		"test":        false,
 	}
 
-	hasCodex := false
-	hasClaude := false
 	for _, a := range agents {
-		if a == "codex" {
-			hasCodex = true
-		}
-		if a == "claude-code" {
-			hasClaude = true
+		if _, ok := expected[a]; ok {
+			expected[a] = true
 		}
 	}
 
-	if !hasCodex {
-		t.Error("Expected codex in available agents")
-	}
-	if !hasClaude {
-		t.Error("Expected claude-code in available agents")
+	for name, found := range expected {
+		if !found {
+			t.Errorf("Expected %s in available agents", name)
+		}
 	}
 }

internal/agent/copilot.go

@@ -0,0 +1,58 @@
+package agent
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+)
+
+// CopilotAgent runs code reviews using the GitHub Copilot CLI
+type CopilotAgent struct {
+	Command string // The copilot command to run (default: "copilot")
+}
+
+// NewCopilotAgent creates a new Copilot agent
+func NewCopilotAgent(command string) *CopilotAgent {
+	if command == "" {
+		command = "copilot"
+	}
+	return &CopilotAgent{Command: command}
+}
+
+func (a *CopilotAgent) Name() string {
+	return "copilot"
+}
+
+func (a *CopilotAgent) CommandName() string {
+	return a.Command
+}
+
+func (a *CopilotAgent) Review(ctx context.Context, repoPath, commitSHA, prompt string) (string, error) {
+	// Use copilot with --prompt for non-interactive mode
+	args := []string{
+		"--prompt", 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 {
+		return "", fmt.Errorf("copilot failed: %w\nstderr: %s", err, stderr.String())
+	}
+
+	output := stdout.String()
+	if len(output) == 0 {
+		return "No review output generated", nil
+	}
+
+	return output, nil
+}
+
+func init() {
+	Register(NewCopilotAgent(""))
+}

internal/agent/gemini.go

@@ -0,0 +1,59 @@
+package agent
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os/exec"
+)
+
+// GeminiAgent runs code reviews using the Gemini CLI
+type GeminiAgent struct {
+	Command string // The gemini command to run (default: "gemini")
+}
+
+// NewGeminiAgent creates a new Gemini agent
+func NewGeminiAgent(command string) *GeminiAgent {
+	if command == "" {
+		command = "gemini"
+	}
+	return &GeminiAgent{Command: command}
+}
+
+func (a *GeminiAgent) Name() string {
+	return "gemini"
+}
+
+func (a *GeminiAgent) CommandName() string {
+	return a.Command
+}
+
+func (a *GeminiAgent) Review(ctx context.Context, repoPath, commitSHA, prompt string) (string, error) {
+	// Use gemini with -p for non-interactive mode
+	// Output goes to stdout
+	args := []string{
+		"-p", 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 {
+		return "", fmt.Errorf("gemini failed: %w\nstderr: %s", err, stderr.String())
+	}
+
+	output := stdout.String()
+	if len(output) == 0 {
+		return "No review output generated", nil
+	}
+
+	return output, nil
+}
+
+func init() {
+	Register(NewGeminiAgent(""))
+}