feat: add GitHub Copilot CLI provider support

README.md

@@ -44,7 +44,7 @@ See the [documentation](https://minicodemonkey.github.io/chief/concepts/how-it-w
 
 ## Requirements
 
-- **[Claude Code CLI](https://docs.anthropic.com/en/docs/claude-code)**, **[Codex CLI](https://developers.openai.com/codex/cli/reference)**, **[OpenCode CLI](https://opencode.ai)**, or **[Gemini CLI](https://github.com/google-gemini/gemini-cli)** installed and authenticated
+- **[Claude Code CLI](https://docs.anthropic.com/en/docs/claude-code)**, **[Codex CLI](https://developers.openai.com/codex/cli/reference)**, **[OpenCode CLI](https://opencode.ai)**, **[Gemini CLI](https://github.com/google-gemini/gemini-cli)**, or **[GitHub Copilot CLI](https://github.com/features/copilot/cli)** installed and authenticated
 
 Use Claude by default, or configure another provider in `.chief/config.yaml`:
 
@@ -56,7 +56,7 @@ agent:
 
 Or run with `chief --agent opencode` or set `CHIEF_AGENT=opencode`.
 
-Supported values for `provider` are: `claude`, `codex`, `opencode`, `cursor`, and `gemini`.
+Supported values for `provider` are: `claude`, `codex`, `opencode`, `cursor`, `gemini`, and `copilot`.
 
 ## License
 

cmd/chief/main.go

@@ -28,7 +28,7 @@ type TUIOptions struct {
 	Merge         bool
 	Force         bool
 	NoRetry       bool
-	Agent         string // --agent claude|codex|opencode|cursor
+	Agent         string // --agent claude|codex|opencode|cursor|gemini|copilot
 	AgentPath     string // --agent-path
 }
 
@@ -134,7 +134,7 @@ func parseAgentFlags(args []string, startIdx int) (agentName, agentPath string,
 				i++
 				agentName = args[i]
 			} else {
-				fmt.Fprintf(os.Stderr, "Error: --agent requires a value (claude, codex, opencode, cursor or gemini)\n")
+				fmt.Fprintf(os.Stderr, "Error: --agent requires a value (claude, codex, opencode, cursor, gemini or copilot)\n")
 				os.Exit(1)
 			}
 		case strings.HasPrefix(arg, "--agent="):
@@ -514,7 +514,7 @@ Commands:
   help                      Show this help message
 
 Global Options:
-  --agent <provider>        Agent CLI to use: claude (default), codex, opencode, cursor, or gemini
+  --agent <provider>        Agent CLI to use: claude (default), codex, opencode, cursor, gemini, or copilot
   --agent-path <path>       Custom path to agent CLI binary
   --max-iterations N, -n N  Set maximum iterations (default: dynamic)
   --no-retry                Disable auto-retry on agent crashes
@@ -542,6 +542,7 @@ Examples:
   chief --verbose           Launch with raw agent output visible
   chief --agent codex       Use Codex CLI instead of Claude
   chief --agent cursor      Use Cursor CLI as agent
+  chief --agent copilot     Use GitHub Copilot CLI as agent
   chief new                 Create PRD in .chief/prds/main/
   chief new auth            Create PRD in .chief/prds/auth/
   chief new auth "JWT authentication for REST API"

docs/concepts/prd-format.md

@@ -23,7 +23,7 @@ Each PRD lives in its own subdirectory inside `.chief/prds/`:
 
 - **`prd.md`** — Written by you, read and updated by Chief. Contains project context and structured user stories.
 - **`progress.md`** — Written by the agent. Tracks what was done, what changed, and what was learned.
-- **`claude.log`** (or `codex.log` / `opencode.log` / `cursor.log`) — Written by Chief. Raw output from the agent for debugging.
+- **Agent log** (`claude.log`, `codex.log`, `opencode.log`, `cursor.log`, `gemini.log`, or `copilot.log`) — Written by Chief. Raw output from the agent for debugging.
 
 ## prd.md — The PRD File
 

docs/guide/installation.md

@@ -54,6 +54,15 @@ To use [Cursor CLI](https://cursor.com/docs/cli/overview) as the agent:
 3. Run `agent login` for authentication.
 4. Run Chief with `chief --agent cursor` or set `CHIEF_AGENT=cursor`, or set `agent.provider: cursor` in `.chief/config.yaml`.
 
+### Option E: GitHub Copilot CLI
+
+To use [GitHub Copilot CLI](https://github.com/features/copilot/cli) as the agent:
+
+1. Install Copilot CLI using the [official instructions](https://docs.github.com/en/copilot/how-tos/copilot-cli/set-up-copilot-cli/install-copilot-cli).
+2. Ensure `copilot` is on your PATH, or set `agent.cliPath` in `.chief/config.yaml`.
+3. Run `copilot login` for authentication.
+4. Run Chief with `chief --agent copilot` or set `CHIEF_AGENT=copilot`, or set `agent.provider: copilot` in `.chief/config.yaml`.
+
 ### Optional: GitHub CLI (`gh`)
 
 If you want Chief to automatically create pull requests when a PRD completes, install the [GitHub CLI](https://cli.github.com/):

docs/guide/quick-start.md

@@ -19,6 +19,8 @@ Before you begin, make sure you have:
   - [Codex CLI](https://developers.openai.com/codex/cli/reference)
   - [OpenCode CLI](https://opencode.ai/docs/)
   - [Cursor CLI](https://cursor.com/docs/cli/overview)
+  - [Gemini CLI](https://github.com/google-gemini/gemini-cli)
+  - [GitHub Copilot CLI](https://github.com/features/copilot/cli)
 - A project you want to work on (or create a new one)
 
 ::: tip Verify your agent CLI is working
@@ -27,6 +29,8 @@ Run the version command for your agent to confirm it's installed:
 - `codex --version` (Codex)
 - `opencode --version` (OpenCode)
 - `agent --version` (Cursor CLI)
+- `gemini --version` (Gemini CLI)
+- `copilot --version` (GitHub Copilot CLI)
 :::
 
 ## Step 1: Install Chief

docs/reference/configuration.md

@@ -14,7 +14,7 @@ Chief stores project-level settings in `.chief/config.yaml`. This file is create
 
 ```yaml
 agent:
-  provider: claude   # or "codex", "opencode", or "cursor"
+  provider: claude   # or "codex", "opencode", "cursor", "gemini", or "copilot"
   cliPath: ""        # optional path to CLI binary
 worktree:
   setup: "npm install"
@@ -27,7 +27,7 @@ onComplete:
 
 | Key | Type | Default | Description |
 |-----|------|---------|-------------|
-| `agent.provider` | string | `"claude"` | Agent CLI to use: `claude`, `codex`, `opencode`, or `cursor` |
+| `agent.provider` | string | `"claude"` | Agent CLI to use: `claude`, `codex`, `opencode`, `cursor`, `gemini`, or `copilot` |
 | `agent.cliPath` | string | `""` | Optional path to the agent binary (e.g. `/usr/local/bin/opencode`). If empty, Chief uses the provider name from PATH. |
 | `worktree.setup` | string | `""` | Shell command to run in new worktrees (e.g., `npm install`, `go mod download`) |
 | `onComplete.push` | bool | `false` | Automatically push the branch to remote when a PRD completes |
@@ -88,7 +88,7 @@ These settings are saved to `.chief/config.yaml` and can be changed at any time
 
 | Flag | Description | Default |
 |------|-------------|---------|
-| `--agent <provider>` | Agent CLI to use: `claude`, `codex`, `opencode`, or `cursor` | From config / env / `claude` |
+| `--agent <provider>` | Agent CLI to use: `claude`, `codex`, `opencode`, `cursor`, `gemini`, or `copilot` | From config / env / `claude` |
 | `--agent-path <path>` | Custom path to the agent CLI binary | From config / env |
 | `--max-iterations <n>`, `-n` | Loop iteration limit | Dynamic |
 | `--no-retry` | Disable auto-retry on agent crashes | `false` |
@@ -100,7 +100,7 @@ When `--max-iterations` is not specified, Chief calculates a dynamic limit based
 
 ## Agent
 
-Chief can use **Claude Code** (default), **Codex CLI**, **OpenCode CLI**, **Cursor CLI**, or **Gemini CLI** as the agent. Choose via:
+Chief can use **Claude Code** (default), **Codex CLI**, **OpenCode CLI**, **Cursor CLI**, **Gemini CLI**, or **GitHub Copilot CLI** as the agent. Choose via:
 
 - **Config:** `agent.provider: opencode` and optionally `agent.cliPath: /path/to/opencode` in `.chief/config.yaml`
 - **Environment:** `CHIEF_AGENT=opencode`, `CHIEF_AGENT_PATH=/path/to/opencode`

docs/troubleshooting/common-issues.md

@@ -51,6 +51,13 @@ Error: OpenCode CLI not found in PATH. Install it or set agent.cliPath in .chief
     cliPath: /path/to/agent
   ```
   Run `agent login`. Verify with `agent --version` (or your `cliPath`).
+- **GitHub Copilot:** Install [GitHub Copilot CLI](https://github.com/features/copilot/cli) and ensure `copilot` is in PATH, or set the path in config:
+  ```yaml
+  agent:
+    provider: copilot
+    cliPath: /usr/local/bin/copilot
+  ```
+  Run `copilot login`. Verify with `copilot --version` (or your `cliPath`).
 
 ## Permission Denied
 
@@ -70,9 +77,9 @@ Chief automatically configures the agent for autonomous operation by disabling p
 
 **Solution:**
 
-1. Check the agent log for errors (the log file matches your agent: `claude.log`, `codex.log`, `opencode.log`, or `cursor.log`):
+1. Check the agent log for errors (the log file matches your agent: `claude.log`, `codex.log`, `opencode.log`, `cursor.log`, `gemini.log`, or `copilot.log`):
    ```bash
-   tail -100 .chief/prds/your-prd/claude.log  # or codex.log / opencode.log / cursor.log
+   tail -100 .chief/prds/your-prd/copilot.log
    ```
 
 2. Manually mark story complete if appropriate by editing `prd.md`:
@@ -92,7 +99,7 @@ Chief automatically configures the agent for autonomous operation by disabling p
 
 1. Check the agent log for what the agent is doing:
    ```bash
-   tail -f .chief/prds/your-prd/claude.log  # or codex.log / opencode.log / cursor.log
+   tail -f .chief/prds/your-prd/copilot.log
    ```
 
 2. Simplify the current story's acceptance criteria
@@ -121,7 +128,7 @@ Chief automatically configures the agent for autonomous operation by disabling p
 
 2. Or investigate why it's taking so many iterations:
    - Story too complex? Split it
-   - Stuck in a loop? Check the agent log (`claude.log`, `codex.log`, `opencode.log`, or `cursor.log`)
+   - Stuck in a loop? Check the matching agent log (for example, `claude.log` or `copilot.log`)
    - Unclear acceptance criteria? Clarify them
 
 ## "No PRD Found"
@@ -262,4 +269,4 @@ If none of these solutions help:
 3. Open a new issue with:
    - Chief version (`chief --version`)
    - Your `prd.md` (sanitized)
-   - Relevant agent log excerpts (e.g. `claude.log`, `codex.log`, `opencode.log`, or `cursor.log`)
+   - Relevant agent log excerpts (for example, `claude.log` or `copilot.log`)

internal/agent/copilot.go

@@ -0,0 +1,88 @@
+package agent
+
+import (
+	"context"
+	"encoding/json"
+	"os/exec"
+	"strings"
+
+	"github.com/minicodemonkey/chief/internal/loop"
+)
+
+// CopilotProvider implements loop.Provider for GitHub Copilot CLI.
+type CopilotProvider struct {
+	cliPath string
+}
+
+// NewCopilotProvider returns a Provider for GitHub Copilot CLI.
+// If cliPath is empty, "copilot" is used.
+func NewCopilotProvider(cliPath string) *CopilotProvider {
+	if cliPath == "" {
+		cliPath = "copilot"
+	}
+	return &CopilotProvider{cliPath: cliPath}
+}
+
+// Name implements loop.Provider.
+func (p *CopilotProvider) Name() string { return "Copilot" }
+
+// CLIPath implements loop.Provider.
+func (p *CopilotProvider) CLIPath() string { return p.cliPath }
+
+// LoopCommand implements loop.Provider.
+func (p *CopilotProvider) LoopCommand(ctx context.Context, prompt, workDir string) *exec.Cmd {
+	cmd := exec.CommandContext(ctx, p.cliPath,
+		"-p", prompt,
+		"--output-format", "json",
+		"--allow-all",
+		"--no-ask-user",
+		"--no-color",
+		"--no-auto-update",
+		"--no-remote",
+		"--no-remote-export",
+	)
+	cmd.Dir = workDir
+	return cmd
+}
+
+// InteractiveCommand implements loop.Provider.
+func (p *CopilotProvider) InteractiveCommand(workDir, prompt string) *exec.Cmd {
+	cmd := exec.Command(p.cliPath, "-i", prompt)
+	cmd.Dir = workDir
+	return cmd
+}
+
+// ParseLine implements loop.Provider.
+func (p *CopilotProvider) ParseLine(line string) *loop.Event {
+	return loop.ParseLineCopilot(line)
+}
+
+// LogFileName implements loop.Provider.
+func (p *CopilotProvider) LogFileName() string { return "copilot.log" }
+
+// CleanOutput extracts complete assistant messages from Copilot's JSONL output.
+func (p *CopilotProvider) CleanOutput(output string) string {
+	output = strings.TrimSpace(output)
+	if output == "" {
+		return output
+	}
+
+	var messages []string
+	for _, line := range strings.Split(output, "\n") {
+		var event struct {
+			Type string `json:"type"`
+			Data struct {
+				Content string `json:"content"`
+			} `json:"data"`
+		}
+		if json.Unmarshal([]byte(line), &event) == nil &&
+			event.Type == "assistant.message" &&
+			event.Data.Content != "" {
+			messages = append(messages, event.Data.Content)
+		}
+	}
+	if len(messages) > 0 {
+		return strings.Join(messages, "\n")
+	}
+	return output
+}

internal/agent/copilot_test.go

@@ -0,0 +1,82 @@
+package agent
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/minicodemonkey/chief/internal/loop"
+)
+
+func TestCopilotProvider(t *testing.T) {
+	p := NewCopilotProvider("")
+	if p.Name() != "Copilot" {
+		t.Errorf("Name() = %q, want Copilot", p.Name())
+	}
+	if p.CLIPath() != "copilot" {
+		t.Errorf("CLIPath() = %q, want copilot", p.CLIPath())
+	}
+	if p.LogFileName() != "copilot.log" {
+		t.Errorf("LogFileName() = %q, want copilot.log", p.LogFileName())
+	}
+
+	custom := NewCopilotProvider("/opt/copilot")
+	if custom.CLIPath() != "/opt/copilot" {
+		t.Errorf("custom CLIPath() = %q, want /opt/copilot", custom.CLIPath())
+	}
+}
+
+func TestCopilotProvider_LoopCommand(t *testing.T) {
+	p := NewCopilotProvider("/bin/copilot")
+	cmd := p.LoopCommand(context.Background(), "build it", "/work")
+
+	wantArgs := []string{
+		"/bin/copilot", "-p", "build it",
+		"--output-format", "json",
+		"--allow-all",
+		"--no-ask-user",
+		"--no-color",
+		"--no-auto-update",
+		"--no-remote",
+		"--no-remote-export",
+	}
+	if strings.Join(cmd.Args, "\x00") != strings.Join(wantArgs, "\x00") {
+		t.Errorf("LoopCommand Args = %v, want %v", cmd.Args, wantArgs)
+	}
+	if cmd.Dir != "/work" {
+		t.Errorf("LoopCommand Dir = %q, want /work", cmd.Dir)
+	}
+}
+
+func TestCopilotProvider_InteractiveCommand(t *testing.T) {
+	p := NewCopilotProvider("/bin/copilot")
+	cmd := p.InteractiveCommand("/work", "review this")
+	wantArgs := []string{"/bin/copilot", "-i", "review this"}
+	if strings.Join(cmd.Args, "\x00") != strings.Join(wantArgs, "\x00") {
+		t.Errorf("InteractiveCommand Args = %v, want %v", cmd.Args, wantArgs)
+	}
+	if cmd.Dir != "/work" {
+		t.Errorf("InteractiveCommand Dir = %q, want /work", cmd.Dir)
+	}
+}
+
+func TestCopilotProvider_ParseLine(t *testing.T) {
+	p := NewCopilotProvider("")
+	event := p.ParseLine(`{"type":"assistant.message","data":{"content":"done <chief-done/>"}}`)
+	if event == nil || event.Type != loop.EventStoryDone {
+		t.Fatalf("ParseLine() = %#v, want EventStoryDone", event)
+	}
+}
+
+func TestCopilotProvider_CleanOutput(t *testing.T) {
+	p := NewCopilotProvider("")
+	output := `{"type":"assistant.message","data":{"content":"first"}}
+{"type":"tool.execution_start","data":{"toolName":"bash"}}
+{"type":"assistant.message","data":{"content":"second"}}`
+	if got := p.CleanOutput(output); got != "first\nsecond" {
+		t.Errorf("CleanOutput() = %q, want %q", got, "first\nsecond")
+	}
+	if got := p.CleanOutput("plain text"); got != "plain text" {
+		t.Errorf("CleanOutput(plain) = %q, want plain text", got)
+	}
+}

internal/agent/resolve.go

@@ -43,8 +43,10 @@ func Resolve(flagAgent, flagPath string, cfg *config.Config) (loop.Provider, err
 		return NewCursorProvider(cliPath), nil
 	case "gemini":
 		return NewGeminiProvider(cliPath), nil
+	case "copilot", "copilot-cli":
+		return NewCopilotProvider(cliPath), nil
 	default:
-		return nil, fmt.Errorf("unknown agent provider %q: expected \"claude\", \"codex\", \"opencode\", \"cursor\", or \"gemini\"", providerName)
+		return nil, fmt.Errorf("unknown agent provider %q: expected \"claude\", \"codex\", \"opencode\", \"cursor\", \"gemini\", or \"copilot\"", providerName)
 	}
 }
 

internal/agent/resolve_test.go

@@ -178,6 +178,23 @@ func TestResolve_gemini(t *testing.T) {
 	}
 }
 
+func TestResolve_copilot(t *testing.T) {
+	for _, name := range []string{"copilot", "copilot-cli"} {
+		got := mustResolve(t, name, "", nil)
+		if got.Name() != "Copilot" {
+			t.Errorf("Resolve(%s) name = %q, want Copilot", name, got.Name())
+		}
+		if got.CLIPath() != "copilot" {
+			t.Errorf("Resolve(%s) CLIPath = %q, want copilot", name, got.CLIPath())
+		}
+	}
+
+	got := mustResolve(t, "copilot", "/usr/local/bin/copilot", nil)
+	if got.CLIPath() != "/usr/local/bin/copilot" {
+		t.Errorf("Resolve(copilot, custom path) CLIPath = %q, want /usr/local/bin/copilot", got.CLIPath())
+	}
+}
+
 func TestResolve_unknownProvider(t *testing.T) {
 	_, err := Resolve("typo", "", nil)
 	if err == nil {
@@ -189,6 +206,9 @@ func TestResolve_unknownProvider(t *testing.T) {
 	if !strings.Contains(err.Error(), "gemini") {
 		t.Errorf("error should mention gemini as a valid option: %v", err)
 	}
+	if !strings.Contains(err.Error(), "copilot") {
+		t.Errorf("error should mention copilot as a valid option: %v", err)
+	}
 }
 
 func TestCheckInstalled_notFound(t *testing.T) {