feat(persona): add role-based review personas

Add persona system for specialized review roles. Each persona defines:
- A specific review focus (security, architecture, documentation)
- Custom system prompt additions
- Personality/tone adjustments

Built-in personas: security, architect, docs
Custom personas: load from JSON via persona-file flag

Includes workspace validation to prevent path traversal attacks.

Closes #51

cmd/review-bot/main.go

@@ -70,6 +70,8 @@ func main() {
 	llmTemp := flag.Float64("llm-temperature", envOrDefaultFloat("LLM_TEMPERATURE", 0), "LLM temperature (0 = server default)")
 	llmTimeout := flag.Int("llm-timeout", envOrDefaultInt("LLM_TIMEOUT", 300), "LLM request timeout in seconds (default 300)")
 	llmProvider := flag.String("llm-provider", envOrDefault("LLM_PROVIDER", "openai"), "LLM API provider: openai or anthropic")
+	personaName := flag.String("persona", envOrDefault("PERSONA", ""), "Built-in persona name (security, architect, docs)")
+	personaFile := flag.String("persona-file", envOrDefault("PERSONA_FILE", ""), "Path to persona JSON file")
 
 	flag.Parse()
 
@@ -91,6 +93,36 @@ func main() {
 		os.Exit(1)
 	}
 
+	// Validate persona flags are mutually exclusive
+	if *personaName != "" && *personaFile != "" {
+		slog.Error("--persona and --persona-file are mutually exclusive")
+		os.Exit(1)
+	}
+
+	// Load persona if specified
+	var persona *review.Persona
+	if *personaName != "" {
+		var err error
+		persona, err = review.LoadBuiltinPersona(*personaName)
+		if err != nil {
+			slog.Error("failed to load persona", "persona", *personaName, "error", err)
+			os.Exit(1)
+		}
+		slog.Info("loaded built-in persona", "persona", persona.Name, "display", persona.DisplayName)
+	} else if *personaFile != "" {
+		resolvedPath, err := validateWorkspacePath(*personaFile, "persona-file")
+		if err != nil {
+			slog.Error("invalid persona-file path", "error", err)
+			os.Exit(1)
+		}
+		persona, err = review.LoadPersona(resolvedPath)
+		if err != nil {
+			slog.Error("failed to load persona file", "file", *personaFile, "error", err)
+			os.Exit(1)
+		}
+		slog.Info("loaded persona from file", "file", *personaFile, "persona", persona.Name)
+	}
+
 	// Validate reviewer-name: only safe characters allowed in sentinel
 	if err := validateReviewerName(*reviewerName); err != nil {
 		slog.Error("invalid reviewer name", "error", err)
@@ -201,34 +233,14 @@ func main() {
 	// Step 6b: Load additional system prompt if specified
 	additionalPrompt := ""
 	if *systemPromptFile != "" {
-		workspace := os.Getenv("GITHUB_WORKSPACE")
-		if workspace == "" {
-			workspace, _ = os.Getwd()
-		}
-		absWorkspace, err := filepath.Abs(workspace)
+		resolvedPath, err := validateWorkspacePath(*systemPromptFile, "system-prompt-file")
 		if err != nil {
-			slog.Error("failed to resolve workspace path", "error", err)
-			os.Exit(1)
-		}
-		promptPath := filepath.Join(absWorkspace, *systemPromptFile)
-		promptPath = filepath.Clean(promptPath)
-		if !strings.HasPrefix(promptPath, absWorkspace+string(filepath.Separator)) && promptPath != absWorkspace {
-			slog.Error("system-prompt-file resolves outside workspace", "path", promptPath, "workspace", absWorkspace)
-			os.Exit(1)
-		}
-		// Resolve symlinks and re-validate to prevent symlink traversal
-		resolvedPath, err := filepath.EvalSymlinks(promptPath)
-		if err != nil {
-			slog.Error("failed to resolve system prompt file", "path", promptPath, "error", err)
-			os.Exit(1)
-		}
-		if !strings.HasPrefix(resolvedPath, absWorkspace+string(filepath.Separator)) && resolvedPath != absWorkspace {
-			slog.Error("system-prompt-file symlink resolves outside workspace", "resolved", resolvedPath, "workspace", absWorkspace)
+			slog.Error("invalid system-prompt-file path", "error", err)
 			os.Exit(1)
 		}
 		data, err := os.ReadFile(resolvedPath)
 		if err != nil {
-			slog.Error("failed to read system prompt file", "path", promptPath, "error", err)
+			slog.Error("failed to read system prompt file", "path", *systemPromptFile, "error", err)
 			os.Exit(1)
 		}
 		additionalPrompt = string(data)
@@ -236,7 +248,13 @@ func main() {
 	}
 
 	// Step 7: Budget-aware prompt assembly
-	systemBase := review.BuildSystemBase()
+	var systemBase string
+	if persona != nil {
+		systemBase = review.BuildPersonaSystemPrompt(persona)
+		slog.Debug("using persona system prompt", "persona", persona.Name)
+	} else {
+		systemBase = review.BuildSystemBase()
+	}
 	if additionalPrompt != "" {
 		systemBase += "\n\n## Additional Review Instructions\n\n" + additionalPrompt
 	}
@@ -293,7 +311,12 @@ func main() {
 	slog.Info("review parsed", "verdict", result.Verdict, "findings", len(result.Findings))
 
 	// Step 10: Format and post review
-	reviewBody := review.FormatMarkdown(result, *reviewerName)
+	var reviewBody string
+	if persona != nil && persona.DisplayName != "" {
+		reviewBody = review.FormatMarkdownWithDisplay(result, persona.DisplayName, *reviewerName)
+	} else {
+		reviewBody = review.FormatMarkdown(result, *reviewerName)
+	}
 
 	// Add commit footer so readers know which commit was evaluated
 	if pr.Head.Sha != "" {
@@ -587,6 +610,43 @@ func validateReviewerName(name string) error {
 	return nil
 }
 
+// validateWorkspacePath ensures a file path is within the workspace and resolves
+// symlinks to prevent traversal attacks. Returns the resolved absolute path or
+// an error if the path is outside the workspace.
+func validateWorkspacePath(path, pathName string) (string, error) {
+	workspace := os.Getenv("GITHUB_WORKSPACE")
+	if workspace == "" {
+		workspace, _ = os.Getwd()
+	}
+	absWorkspace, err := filepath.Abs(workspace)
+	if err != nil {
+		return "", fmt.Errorf("failed to resolve workspace path: %w", err)
+	}
+
+	// Join and clean the path
+	fullPath := filepath.Join(absWorkspace, path)
+	fullPath = filepath.Clean(fullPath)
+
+	// Check path is within workspace using filepath.Rel (more robust than HasPrefix)
+	rel, err := filepath.Rel(absWorkspace, fullPath)
+	if err != nil || strings.HasPrefix(rel, "..") {
+		return "", fmt.Errorf("%s resolves outside workspace: path=%s workspace=%s", pathName, fullPath, absWorkspace)
+	}
+
+	// Resolve symlinks and re-validate to prevent symlink traversal
+	resolvedPath, err := filepath.EvalSymlinks(fullPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to resolve %s: %w", pathName, err)
+	}
+
+	relResolved, err := filepath.Rel(absWorkspace, resolvedPath)
+	if err != nil || strings.HasPrefix(relResolved, "..") {
+		return "", fmt.Errorf("%s symlink resolves outside workspace: resolved=%s workspace=%s", pathName, resolvedPath, absWorkspace)
+	}
+
+	return resolvedPath, nil
+}
+
 // buildSupersededBody creates the body for a superseded review: struck-through banner
 // with collapsed original content and the commit it was evaluated against.
 func buildSupersededBody(originalBody, commitSHA, newReviewURL, sentinel string) string {

cmd/review-bot/main_test.go

@@ -6,6 +6,7 @@ import (
 	"log/slog"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -45,6 +46,113 @@ func TestValidateReviewerName(t *testing.T) {
 	}
 }
 
+func TestValidateWorkspacePath(t *testing.T) {
+	// Create a temp directory as our workspace
+	tmpDir := t.TempDir()
+
+	// Create a valid file inside the workspace
+	validFile := filepath.Join(tmpDir, "valid.json")
+	if err := os.WriteFile(validFile, []byte("{}"), 0644); err != nil {
+		t.Fatalf("failed to create test file: %v", err)
+	}
+
+	// Create a subdirectory with a file
+	subDir := filepath.Join(tmpDir, "subdir")
+	if err := os.MkdirAll(subDir, 0755); err != nil {
+		t.Fatalf("failed to create subdir: %v", err)
+	}
+	nestedFile := filepath.Join(subDir, "nested.json")
+	if err := os.WriteFile(nestedFile, []byte("{}"), 0644); err != nil {
+		t.Fatalf("failed to create nested file: %v", err)
+	}
+
+	// Create a symlink pointing outside the workspace
+	symlinkPath := filepath.Join(tmpDir, "evil-symlink.json")
+	if err := os.Symlink("/etc/passwd", symlinkPath); err != nil {
+		t.Fatalf("failed to create symlink: %v", err)
+	}
+
+	// Save and restore GITHUB_WORKSPACE
+	origWorkspace := os.Getenv("GITHUB_WORKSPACE")
+	defer os.Setenv("GITHUB_WORKSPACE", origWorkspace)
+
+	tests := []struct {
+		name      string
+		workspace string
+		path      string
+		wantErr   bool
+		errMatch  string
+	}{
+		{
+			name:      "valid relative path",
+			workspace: tmpDir,
+			path:      "valid.json",
+			wantErr:   false,
+		},
+		{
+			name:      "valid nested path",
+			workspace: tmpDir,
+			path:      "subdir/nested.json",
+			wantErr:   false,
+		},
+		{
+			name:      "path traversal attempt",
+			workspace: tmpDir,
+			path:      "../../../etc/passwd",
+			wantErr:   true,
+			errMatch:  "resolves outside workspace",
+		},
+		{
+			name:      "absolute path gets normalized to relative",
+			workspace: tmpDir,
+			path:      "/etc/passwd",
+			wantErr:   true,
+			errMatch:  "failed to resolve", // filepath.Join strips leading / making it <workspace>/etc/passwd which doesn't exist
+		},
+		{
+			name:      "nonexistent file",
+			workspace: tmpDir,
+			path:      "nonexistent.json",
+			wantErr:   true,
+			errMatch:  "failed to resolve",
+		},
+		{
+			name:      "symlink escaping workspace",
+			workspace: tmpDir,
+			path:      "evil-symlink.json",
+			wantErr:   true,
+			errMatch:  "symlink resolves outside workspace",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			os.Setenv("GITHUB_WORKSPACE", tc.workspace)
+			resolved, err := validateWorkspacePath(tc.path, "test-file")
+
+			if tc.wantErr {
+				if err == nil {
+					t.Errorf("expected error for %q, got nil", tc.path)
+				} else if tc.errMatch != "" && !strings.Contains(err.Error(), tc.errMatch) {
+					t.Errorf("error %q should contain %q", err.Error(), tc.errMatch)
+				}
+			} else {
+				if err != nil {
+					t.Errorf("expected no error for %q, got %v", tc.path, err)
+				}
+				if resolved == "" {
+					t.Error("expected non-empty resolved path")
+				}
+				// Verify resolved path is within workspace
+				if !strings.HasPrefix(resolved, tc.workspace) {
+					t.Errorf("resolved path %q not within workspace %q", resolved, tc.workspace)
+				}
+			}
+		})
+	}
+}
+
+
 func makeReview(id int64, login, state string, stale bool, body string) gitea.Review {
 	r := gitea.Review{
 		ID:    id,