feat: load personas from target repo .review-bot/personas/

Implements #60.

- Add ParsePersonaBytes() for parsing personas from byte data
- Add LoadRepoPersonas() to fetch personas from repo via Gitea API
- Add MergePersonas() to combine built-in and repo personas
- Add GetBuiltinPersonasMap() helper
- Update main.go to load repo personas first, fall back to built-in
- Add giteaClientAdapter to bridge gitea.Client to review.GiteaClient

When --persona is specified, the bot now:
1. Attempts to fetch personas from .review-bot/personas/*.yaml
2. If the named persona exists in the repo, uses it
3. Otherwise falls back to built-in personas

This allows repos to define domain-specific personas (e.g., trading
experts for gargoyle, crypto experts for kms-lite) without modifying
the review-bot codebase.

cmd/review-bot/main.go

@@ -116,29 +116,7 @@ func main() {
 		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)
-	}
+	// NOTE: Persona loading deferred until after Gitea client init to support repo personas
 
 	// Validate reviewer-name: only safe characters allowed in sentinel
 	if err := validateReviewerName(*reviewerName); err != nil {
@@ -196,6 +174,41 @@ func main() {
 	ctx, cancel := context.WithTimeout(context.Background(), overallTimeout)
 	defer cancel()
 
+	// Load persona if specified (after Gitea client init to support repo personas)
+	var persona *review.Persona
+	if *personaName != "" {
+		// Try loading from repo first, then fall back to built-in
+		repoPersonas, err := review.LoadRepoPersonas(ctx, newGiteaClientAdapter(giteaClient), owner, repoName)
+		if err != nil {
+			slog.Warn("could not load repo personas", "repo", owner+"/"+repoName, "error", err)
+			// Continue with built-in personas only
+		}
+		if p, ok := repoPersonas[*personaName]; ok {
+			persona = p
+			slog.Info("loaded repo persona", "persona", persona.Name, "display", persona.DisplayName, "repo", owner+"/"+repoName)
+		} else {
+			// Fall back to built-in
+			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)
+	}
+
 	slog.Info("reviewing pull request", "pr", prNumber, "repo", fmt.Sprintf("%s/%s", owner, repoName))
 
 	// Step 1: Fetch PR metadata
@@ -783,3 +796,32 @@ func shouldSkipStaleReview(evaluatedSHA, currentSHA string) bool {
 	}
 	return evaluatedSHA != currentSHA
 }
+
+// giteaClientAdapter adapts gitea.Client to review.GiteaClient interface.
+type giteaClientAdapter struct {
+	client *gitea.Client
+}
+
+func newGiteaClientAdapter(c *gitea.Client) *giteaClientAdapter {
+	return &giteaClientAdapter{client: c}
+}
+
+func (a *giteaClientAdapter) ListContents(ctx context.Context, owner, repo, path string) ([]review.ContentEntry, error) {
+	entries, err := a.client.ListContents(ctx, owner, repo, path)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]review.ContentEntry, len(entries))
+	for i, e := range entries {
+		result[i] = review.ContentEntry{
+			Name: e.Name,
+			Path: e.Path,
+			Type: e.Type,
+		}
+	}
+	return result, nil
+}
+
+func (a *giteaClientAdapter) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
+	return a.client.GetFileContent(ctx, owner, repo, filepath)
+}

review/persona.go

@@ -224,6 +224,13 @@ func checkYAMLDepth(node *yaml.Node, depth, maxDepth, maxNodes int, seen map[*ya
 	return nil
 }
 
+// ParsePersonaBytes parses persona data from bytes with a source label for errors.
+// This is useful for parsing personas fetched from external sources (e.g., Gitea API)
+// without requiring filesystem access. Format is detected by source extension.
+func ParsePersonaBytes(data []byte, source string) (*Persona, error) {
+	return parsePersona(data, source)
+}
+
 func validatePersona(p *Persona, source string) error {
 	if p.Name == "" {
 		return fmt.Errorf("persona %s: name is required", source)

review/repo_persona.go

@@ -0,0 +1,138 @@
+package review
+
+import (
+	"context"
+	"log/slog"
+	"strings"
+)
+
+// RepoPersonaPath is the directory path where repo-specific personas are stored.
+const RepoPersonaPath = ".review-bot/personas"
+
+// GiteaClient defines the subset of gitea.Client methods needed for loading repo personas.
+// This interface allows for easier testing and decouples the review package from gitea.
+type GiteaClient interface {
+	ListContents(ctx context.Context, owner, repo, path string) ([]ContentEntry, error)
+	GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error)
+}
+
+// ContentEntry represents a file or directory entry from the contents API.
+// This mirrors gitea.ContentEntry to avoid import cycles.
+type ContentEntry struct {
+	Name string `json:"name"`
+	Path string `json:"path"`
+	Type string `json:"type"` // "file" or "dir"
+}
+
+// LoadRepoPersonas fetches personas from a repository's .review-bot/personas/ directory.
+// Returns an empty map (not nil) if the directory doesn't exist or is empty.
+// Individual parse failures are logged and skipped; the remaining personas are still returned.
+// Auth errors and other non-404 errors are propagated.
+func LoadRepoPersonas(ctx context.Context, client GiteaClient, owner, repo string) (map[string]*Persona, error) {
+	result := make(map[string]*Persona)
+
+	entries, err := client.ListContents(ctx, owner, repo, RepoPersonaPath)
+	if err != nil {
+		// Check if this is a 404 (directory doesn't exist) - expected case
+		if isNotFoundError(err) {
+			slog.Debug("no repo personas directory found", "repo", owner+"/"+repo)
+			return result, nil
+		}
+		// Other errors (auth, server) should propagate
+		return nil, err
+	}
+
+	if len(entries) == 0 {
+		slog.Debug("repo personas directory is empty", "repo", owner+"/"+repo)
+		return result, nil
+	}
+
+	for _, entry := range entries {
+		if entry.Type != "file" {
+			continue
+		}
+		// Only process YAML files
+		if !isYAMLFile(entry.Name) {
+			continue
+		}
+
+		content, err := client.GetFileContent(ctx, owner, repo, entry.Path)
+		if err != nil {
+			slog.Warn("could not fetch repo persona file",
+				"file", entry.Path,
+				"repo", owner+"/"+repo,
+				"error", err)
+			continue
+		}
+
+		persona, err := ParsePersonaBytes([]byte(content), entry.Path)
+		if err != nil {
+			slog.Warn("could not parse repo persona file",
+				"file", entry.Path,
+				"repo", owner+"/"+repo,
+				"error", err)
+			continue
+		}
+
+		result[persona.Name] = persona
+		slog.Debug("loaded repo persona",
+			"name", persona.Name,
+			"file", entry.Path,
+			"repo", owner+"/"+repo)
+	}
+
+	return result, nil
+}
+
+// MergePersonas combines built-in personas with repo personas.
+// Repo personas take precedence on name collision.
+// Returns a new map; inputs are not modified.
+func MergePersonas(builtin, repo map[string]*Persona) map[string]*Persona {
+	result := make(map[string]*Persona, len(builtin)+len(repo))
+
+	// Copy built-in personas first
+	for name, p := range builtin {
+		result[name] = p
+	}
+
+	// Overlay repo personas (override on collision)
+	for name, p := range repo {
+		if _, exists := result[name]; exists {
+			slog.Debug("repo persona overrides built-in", "name", name)
+		}
+		result[name] = p
+	}
+
+	return result
+}
+
+// GetBuiltinPersonasMap returns all built-in personas as a map keyed by name.
+// Returns an empty map (not nil) if loading fails.
+func GetBuiltinPersonasMap() map[string]*Persona {
+	result := make(map[string]*Persona)
+	for _, name := range ListBuiltinPersonas() {
+		p, err := LoadBuiltinPersona(name)
+		if err != nil {
+			slog.Warn("could not load built-in persona", "name", name, "error", err)
+			continue
+		}
+		result[name] = p
+	}
+	return result
+}
+
+// isYAMLFile checks if a filename has a YAML extension.
+func isYAMLFile(name string) bool {
+	lower := strings.ToLower(name)
+	return strings.HasSuffix(lower, ".yaml") || strings.HasSuffix(lower, ".yml")
+}
+
+// isNotFoundError checks if an error represents a 404 response.
+// This is a string-based heuristic since we don't have access to gitea.APIError here.
+func isNotFoundError(err error) bool {
+	if err == nil {
+		return false
+	}
+	errStr := err.Error()
+	return strings.Contains(errStr, "HTTP 404") || strings.Contains(errStr, "not found")
+}

review/repo_persona_test.go

@@ -0,0 +1,410 @@
+package review
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestParsePersonaBytes(t *testing.T) {
+	tests := []struct {
+		name       string
+		data       string
+		source     string
+		wantName   string
+		wantErr    string
+	}{
+		{
+			name: "valid yaml",
+			data: `name: test
+identity: test identity
+focus:
+  - testing
+`,
+			source:   "test.yaml",
+			wantName: "test",
+		},
+		{
+			name:    "missing name",
+			data:    "identity: test\n",
+			source:  "test.yaml",
+			wantErr: "name is required",
+		},
+		{
+			name:    "invalid yaml",
+			data:    "not: valid:\n  yaml: [broken",
+			source:  "test.yaml",
+			wantErr: "parse",
+		},
+		{
+			name: "json format by extension",
+			data: `{"name": "jsontest", "identity": "json identity"}`,
+			source:   "test.json",
+			wantName: "jsontest",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p, err := ParsePersonaBytes([]byte(tt.data), tt.source)
+			if tt.wantErr != "" {
+				if err == nil {
+					t.Fatalf("expected error containing %q, got nil", tt.wantErr)
+				}
+				if !strings.Contains(err.Error(), tt.wantErr) {
+					t.Errorf("error = %q, want containing %q", err.Error(), tt.wantErr)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if p.Name != tt.wantName {
+				t.Errorf("Name = %q, want %q", p.Name, tt.wantName)
+			}
+		})
+	}
+}
+
+// mockGiteaClient implements GiteaClient for testing.
+type mockGiteaClient struct {
+	contents map[string][]ContentEntry // path -> entries
+	files    map[string]string         // path -> content
+	listErr  error
+	fileErr  map[string]error // path -> error
+}
+
+func (m *mockGiteaClient) ListContents(ctx context.Context, owner, repo, path string) ([]ContentEntry, error) {
+	if m.listErr != nil {
+		return nil, m.listErr
+	}
+	entries, ok := m.contents[path]
+	if !ok {
+		return nil, errors.New("list contents .review-bot/personas: HTTP 404: not found")
+	}
+	return entries, nil
+}
+
+func (m *mockGiteaClient) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
+	if m.fileErr != nil {
+		if err, ok := m.fileErr[filepath]; ok {
+			return "", err
+		}
+	}
+	content, ok := m.files[filepath]
+	if !ok {
+		return "", errors.New("HTTP 404: file not found")
+	}
+	return content, nil
+}
+
+func TestLoadRepoPersonas(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("directory not found returns empty map", func(t *testing.T) {
+		client := &mockGiteaClient{} // No contents configured -> 404
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if personas == nil {
+			t.Error("expected empty map, got nil")
+		}
+		if len(personas) != 0 {
+			t.Errorf("expected 0 personas, got %d", len(personas))
+		}
+	})
+
+	t.Run("empty directory returns empty map", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {},
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(personas) != 0 {
+			t.Errorf("expected 0 personas, got %d", len(personas))
+		}
+	})
+
+	t.Run("loads valid personas", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {
+					{Name: "trading.yaml", Path: ".review-bot/personas/trading.yaml", Type: "file"},
+					{Name: "crypto.yaml", Path: ".review-bot/personas/crypto.yaml", Type: "file"},
+				},
+			},
+			files: map[string]string{
+				".review-bot/personas/trading.yaml": `name: trading
+display_name: Trading Expert
+identity: You are a trading expert.
+focus:
+  - order handling
+  - risk management
+`,
+				".review-bot/personas/crypto.yaml": `name: crypto
+display_name: Crypto Expert
+identity: You are a cryptography expert.
+focus:
+  - key management
+  - encryption
+`,
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(personas) != 2 {
+			t.Fatalf("expected 2 personas, got %d", len(personas))
+		}
+		if personas["trading"] == nil {
+			t.Error("expected trading persona")
+		}
+		if personas["crypto"] == nil {
+			t.Error("expected crypto persona")
+		}
+		if personas["trading"].DisplayName != "Trading Expert" {
+			t.Errorf("trading display name = %q, want %q", personas["trading"].DisplayName, "Trading Expert")
+		}
+	})
+
+	t.Run("skips invalid persona files", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {
+					{Name: "valid.yaml", Path: ".review-bot/personas/valid.yaml", Type: "file"},
+					{Name: "invalid.yaml", Path: ".review-bot/personas/invalid.yaml", Type: "file"},
+				},
+			},
+			files: map[string]string{
+				".review-bot/personas/valid.yaml": `name: valid
+identity: Valid persona
+`,
+				".review-bot/personas/invalid.yaml": "not valid yaml: [broken",
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		// Should have the valid one, skip the invalid
+		if len(personas) != 1 {
+			t.Fatalf("expected 1 persona (skipped invalid), got %d", len(personas))
+		}
+		if personas["valid"] == nil {
+			t.Error("expected valid persona")
+		}
+	})
+
+	t.Run("skips non-yaml files", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {
+					{Name: "persona.yaml", Path: ".review-bot/personas/persona.yaml", Type: "file"},
+					{Name: "README.md", Path: ".review-bot/personas/README.md", Type: "file"},
+					{Name: "notes.txt", Path: ".review-bot/personas/notes.txt", Type: "file"},
+				},
+			},
+			files: map[string]string{
+				".review-bot/personas/persona.yaml": `name: test
+identity: Test persona
+`,
+				".review-bot/personas/README.md": "# Personas\n\nPut your personas here.",
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(personas) != 1 {
+			t.Fatalf("expected 1 persona (yaml only), got %d", len(personas))
+		}
+	})
+
+	t.Run("skips subdirectories", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {
+					{Name: "persona.yaml", Path: ".review-bot/personas/persona.yaml", Type: "file"},
+					{Name: "subdir", Path: ".review-bot/personas/subdir", Type: "dir"},
+				},
+			},
+			files: map[string]string{
+				".review-bot/personas/persona.yaml": `name: test
+identity: Test persona
+`,
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(personas) != 1 {
+			t.Fatalf("expected 1 persona (files only), got %d", len(personas))
+		}
+	})
+
+	t.Run("propagates auth errors", func(t *testing.T) {
+		client := &mockGiteaClient{
+			listErr: errors.New("HTTP 401: unauthorized"),
+		}
+		_, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err == nil {
+			t.Fatal("expected error for auth failure")
+		}
+		if !strings.Contains(err.Error(), "401") {
+			t.Errorf("error = %q, want containing '401'", err.Error())
+		}
+	})
+
+	t.Run("skips files that fail to fetch", func(t *testing.T) {
+		client := &mockGiteaClient{
+			contents: map[string][]ContentEntry{
+				RepoPersonaPath: {
+					{Name: "good.yaml", Path: ".review-bot/personas/good.yaml", Type: "file"},
+					{Name: "bad.yaml", Path: ".review-bot/personas/bad.yaml", Type: "file"},
+				},
+			},
+			files: map[string]string{
+				".review-bot/personas/good.yaml": `name: good
+identity: Good persona
+`,
+			},
+			fileErr: map[string]error{
+				".review-bot/personas/bad.yaml": errors.New("HTTP 500: internal server error"),
+			},
+		}
+		personas, err := LoadRepoPersonas(ctx, client, "owner", "repo")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if len(personas) != 1 {
+			t.Fatalf("expected 1 persona (skipped failed fetch), got %d", len(personas))
+		}
+	})
+}
+
+func TestMergePersonas(t *testing.T) {
+	builtin := map[string]*Persona{
+		"security": {Name: "security", Identity: "Built-in security"},
+		"docs":     {Name: "docs", Identity: "Built-in docs"},
+	}
+	repo := map[string]*Persona{
+		"security": {Name: "security", Identity: "Repo security override"},
+		"trading":  {Name: "trading", Identity: "Repo trading"},
+	}
+
+	merged := MergePersonas(builtin, repo)
+
+	t.Run("repo overrides builtin on collision", func(t *testing.T) {
+		if merged["security"].Identity != "Repo security override" {
+			t.Errorf("security identity = %q, want repo override", merged["security"].Identity)
+		}
+	})
+
+	t.Run("builtin preserved when no collision", func(t *testing.T) {
+		if merged["docs"].Identity != "Built-in docs" {
+			t.Errorf("docs identity = %q, want built-in", merged["docs"].Identity)
+		}
+	})
+
+	t.Run("repo-only persona added", func(t *testing.T) {
+		if merged["trading"] == nil {
+			t.Error("expected trading persona from repo")
+		}
+		if merged["trading"].Identity != "Repo trading" {
+			t.Errorf("trading identity = %q, want repo", merged["trading"].Identity)
+		}
+	})
+
+	t.Run("original maps not modified", func(t *testing.T) {
+		if builtin["trading"] != nil {
+			t.Error("builtin map was modified")
+		}
+		if len(repo) != 2 {
+			t.Error("repo map was modified")
+		}
+	})
+}
+
+func TestGetBuiltinPersonasMap(t *testing.T) {
+	personas := GetBuiltinPersonasMap()
+
+	if len(personas) == 0 {
+		t.Fatal("expected at least one built-in persona")
+	}
+
+	// Verify expected personas exist
+	expected := []string{"security", "architect", "docs"}
+	for _, name := range expected {
+		if personas[name] == nil {
+			t.Errorf("expected built-in persona %q", name)
+		}
+	}
+
+	// Verify personas are valid
+	for name, p := range personas {
+		if p.Name != name {
+			t.Errorf("persona %q has mismatched name %q", name, p.Name)
+		}
+		if p.Identity == "" {
+			t.Errorf("persona %q has empty identity", name)
+		}
+	}
+}
+
+func TestIsYAMLFile(t *testing.T) {
+	tests := []struct {
+		name string
+		want bool
+	}{
+		{"test.yaml", true},
+		{"test.yml", true},
+		{"test.YAML", true},
+		{"test.YML", true},
+		{"test.json", false},
+		{"test.md", false},
+		{"test.txt", false},
+		{"yaml", false},
+		{"yaml.md", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := isYAMLFile(tt.name); got != tt.want {
+				t.Errorf("isYAMLFile(%q) = %v, want %v", tt.name, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsNotFoundError(t *testing.T) {
+	tests := []struct {
+		err  error
+		want bool
+	}{
+		{nil, false},
+		{errors.New("HTTP 404: not found"), true},
+		{errors.New("something not found"), true},
+		{errors.New("HTTP 401: unauthorized"), false},
+		{errors.New("connection refused"), false},
+	}
+
+	for _, tt := range tests {
+		name := "nil"
+		if tt.err != nil {
+			name = tt.err.Error()
+		}
+		t.Run(name, func(t *testing.T) {
+			if got := isNotFoundError(tt.err); got != tt.want {
+				t.Errorf("isNotFoundError(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}