fix: address review feedback on persona feature

MAJOR fixes:
- Remove external YAML dependency (github.com/goccy/go-yaml)
  Per project convention: Go standard library only, zero dependencies.
  Convert all persona files from YAML to JSON format.
- Fix TestValidateWorkspacePath error expectation
  Go 1.21+ filepath.Join normalizes absolute paths differently.

MINOR fixes:
- Remove custom contains helper in persona_test.go (use strings.Contains)
- Add Unicode-safe CapitalizeFirst function for header titles
- ListBuiltinPersonas returns empty slice instead of nil on error
- Fix test comment about filepath.Join behavior

Documentation:
- Update README to reflect JSON-only persona format
- Update design doc with note about JSON decision
- Fix action.yml description for persona-file input

review/formatter.go

@@ -37,7 +37,7 @@ func FormatMarkdownWithDisplay(result *ReviewResult, displayName, sentinelName s
 	}
 
 	if headerName != "" {
-		title := strings.ToUpper(headerName[:1]) + headerName[1:]
+		title := CapitalizeFirst(headerName)
 		sb.WriteString(fmt.Sprintf("# %s Review\n\n", title))
 	}
 

review/persona.go

@@ -5,37 +5,34 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
-	"path/filepath"
 	"strings"
-
-	"github.com/goccy/go-yaml"
+	"unicode/utf8"
 )
 
-//go:embed personas/*.yaml
+//go:embed personas/*.json
 var embeddedPersonas embed.FS
 
 // Persona defines a specialized review role with focused expertise.
 type Persona struct {
-	Name         string   `json:"name" yaml:"name"`
-	DisplayName  string   `json:"display_name" yaml:"display_name"`
-	ModelPref    string   `json:"model_preference,omitempty" yaml:"model_preference,omitempty"`
-	Identity     string   `json:"identity" yaml:"identity"`
-	Focus        []string `json:"focus" yaml:"focus"`
-	Ignore       []string `json:"ignore" yaml:"ignore"`
-	Severity     Severity `json:"severity" yaml:"severity"`
-	OutputFormat string   `json:"output_format,omitempty" yaml:"output_format,omitempty"`
+	Name         string   `json:"name"`
+	DisplayName  string   `json:"display_name"`
+	ModelPref    string   `json:"model_preference,omitempty"`
+	Identity     string   `json:"identity"`
+	Focus        []string `json:"focus"`
+	Ignore       []string `json:"ignore"`
+	Severity     Severity `json:"severity"`
+	OutputFormat string   `json:"output_format,omitempty"`
 }
 
 // Severity defines what constitutes each severity level for this persona.
 // These are prompt guidance for the LLM, not output format changes.
 type Severity struct {
-	Major string `json:"major" yaml:"major"`
-	Minor string `json:"minor" yaml:"minor"`
-	Nit   string `json:"nit" yaml:"nit"`
+	Major string `json:"major"`
+	Minor string `json:"minor"`
+	Nit   string `json:"nit"`
 }
 
-// LoadPersona loads a persona from a file path.
-// Supports both YAML (.yaml, .yml) and JSON (.json) formats.
+// LoadPersona loads a persona from a JSON file path.
 func LoadPersona(path string) (*Persona, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -47,7 +44,7 @@ func LoadPersona(path string) (*Persona, error) {
 // LoadBuiltinPersona loads a built-in persona by name.
 // Returns an error if the persona doesn't exist.
 func LoadBuiltinPersona(name string) (*Persona, error) {
-	filename := name + ".yaml"
+	filename := name + ".json"
 	data, err := embeddedPersonas.ReadFile("personas/" + filename) // embed.FS paths use forward slashes per io/fs spec
 	if err != nil {
 		available := ListBuiltinPersonas()
@@ -57,10 +54,11 @@ func LoadBuiltinPersona(name string) (*Persona, error) {
 }
 
 // ListBuiltinPersonas returns the names of all built-in personas.
+// Returns an empty slice if the embedded directory cannot be read.
 func ListBuiltinPersonas() []string {
 	entries, err := embeddedPersonas.ReadDir("personas")
 	if err != nil {
-		return nil
+		return []string{}
 	}
 	var names []string
 	for _, e := range entries {
@@ -68,10 +66,8 @@ func ListBuiltinPersonas() []string {
 			continue
 		}
 		name := e.Name()
-		if strings.HasSuffix(name, ".yaml") {
-			names = append(names, strings.TrimSuffix(name, ".yaml"))
-		} else if strings.HasSuffix(name, ".yml") {
-			names = append(names, strings.TrimSuffix(name, ".yml"))
+		if strings.HasSuffix(name, ".json") {
+			names = append(names, strings.TrimSuffix(name, ".json"))
 		}
 	}
 	return names
@@ -79,20 +75,9 @@ func ListBuiltinPersonas() []string {
 
 func parsePersona(data []byte, source string) (*Persona, error) {
 	var p Persona
-	
-	// Determine format by extension or try YAML first (it's a superset of JSON)
-	ext := strings.ToLower(filepath.Ext(source))
-	if ext == ".json" {
-		if err := json.Unmarshal(data, &p); err != nil {
-			return nil, fmt.Errorf("parse persona %s: %w", source, err)
-		}
-	} else {
-		// YAML (also handles .yaml, .yml, and builtin: prefix)
-		if err := yaml.Unmarshal(data, &p); err != nil {
-			return nil, fmt.Errorf("parse persona %s: %w", source, err)
-		}
+	if err := json.Unmarshal(data, &p); err != nil {
+		return nil, fmt.Errorf("parse persona %s: %w", source, err)
 	}
-	
 	if err := validatePersona(&p, source); err != nil {
 		return nil, err
 	}
@@ -112,3 +97,16 @@ func validatePersona(p *Persona, source string) error {
 	}
 	return nil
 }
+
+// CapitalizeFirst capitalizes the first rune of a string in a Unicode-safe way.
+// Returns the original string if it's empty.
+func CapitalizeFirst(s string) string {
+	if s == "" {
+		return s
+	}
+	r, size := utf8.DecodeRuneInString(s)
+	if r == utf8.RuneError {
+		return s
+	}
+	return strings.ToUpper(string(r)) + s[size:]
+}

review/persona_test.go

@@ -87,26 +87,22 @@ func TestListBuiltinPersonas(t *testing.T) {
 	}
 }
 
-func TestLoadPersonaFromYAMLFile(t *testing.T) {
+func TestLoadPersonaFromJSONFile(t *testing.T) {
 	dir := t.TempDir()
-	path := filepath.Join(dir, "test.yaml")
+	path := filepath.Join(dir, "test.json")
 
-	content := `
-name: test
-display_name: Test Persona
-identity: |
-  You are a test persona.
-  Multi-line identity works.
-focus:
-  - testing
-  - validation
-ignore:
-  - nothing
-severity:
-  major: Big problems
-  minor: Small problems
-  nit: Tiny problems
-`
+	content := `{
+		"name": "test",
+		"display_name": "Test Persona",
+		"identity": "You are a test persona.\nMulti-line identity works.",
+		"focus": ["testing", "validation"],
+		"ignore": ["nothing"],
+		"severity": {
+			"major": "Big problems",
+			"minor": "Small problems",
+			"nit": "Tiny problems"
+		}
+	}`
 
 	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
 		t.Fatalf("failed to write test file: %v", err)
@@ -131,59 +127,25 @@ severity:
 	}
 }
 
-func TestLoadPersonaFromJSONFile(t *testing.T) {
-	dir := t.TempDir()
-	path := filepath.Join(dir, "test.json")
-
-	content := `{
-		"name": "test",
-		"display_name": "Test Persona",
-		"identity": "You are a test persona.",
-		"focus": ["testing"],
-		"ignore": ["nothing"],
-		"severity": {
-			"major": "Big problems",
-			"minor": "Small problems",
-			"nit": "Tiny problems"
-		}
-	}`
-
-	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
-		t.Fatalf("failed to write test file: %v", err)
-	}
-
-	p, err := LoadPersona(path)
-	if err != nil {
-		t.Fatalf("LoadPersona failed: %v", err)
-	}
-
-	if p.Name != "test" {
-		t.Errorf("Name = %q, want %q", p.Name, "test")
-	}
-	if p.DisplayName != "Test Persona" {
-		t.Errorf("DisplayName = %q, want %q", p.DisplayName, "Test Persona")
-	}
-}
-
 func TestLoadPersonaValidation(t *testing.T) {
 	tests := []struct {
 		name    string
-		yaml    string
+		json    string
 		wantErr string
 	}{
 		{
 			name:    "missing name",
-			yaml:    "identity: test",
+			json:    `{"identity": "test"}`,
 			wantErr: "name is required",
 		},
 		{
 			name:    "missing identity",
-			yaml:    "name: test",
+			json:    `{"name": "test"}`,
 			wantErr: "identity is required",
 		},
 		{
 			name: "display_name defaults to name",
-			yaml: "name: test\nidentity: test identity",
+			json: `{"name": "test", "identity": "test identity"}`,
 			// No error expected - should succeed
 		},
 	}
@@ -191,8 +153,8 @@ func TestLoadPersonaValidation(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			dir := t.TempDir()
-			path := filepath.Join(dir, "test.yaml")
-			if err := os.WriteFile(path, []byte(tt.yaml), 0644); err != nil {
+			path := filepath.Join(dir, "test.json")
+			if err := os.WriteFile(path, []byte(tt.json), 0644); err != nil {
 				t.Fatalf("failed to write test file: %v", err)
 			}
 
@@ -222,21 +184,56 @@ func TestLoadPersonaValidation(t *testing.T) {
 }
 
 func TestLoadPersonaFileNotFound(t *testing.T) {
-	_, err := LoadPersona("/nonexistent/path/persona.yaml")
+	_, err := LoadPersona("/nonexistent/path/persona.json")
 	if err == nil {
 		t.Error("expected error for nonexistent file")
 	}
 }
 
-func TestLoadPersonaInvalidYAML(t *testing.T) {
+func TestLoadPersonaInvalidJSON(t *testing.T) {
 	dir := t.TempDir()
-	path := filepath.Join(dir, "invalid.yaml")
-	if err := os.WriteFile(path, []byte("not: valid: yaml: here"), 0644); err != nil {
+	path := filepath.Join(dir, "invalid.json")
+	if err := os.WriteFile(path, []byte("not valid json {"), 0644); err != nil {
 		t.Fatalf("failed to write test file: %v", err)
 	}
 
 	_, err := LoadPersona(path)
 	if err == nil {
-		t.Error("expected error for invalid YAML")
+		t.Error("expected error for invalid JSON")
+	}
+}
+
+func TestCapitalizeFirst(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"hello", "Hello"},
+		{"Hello", "Hello"},
+		{"HELLO", "HELLO"},
+		{"a", "A"},
+		{"", ""},
+		{"日本語", "日本語"}, // Non-ASCII: Japanese doesn't have case
+		{"über", "Über"},   // German umlaut
+		{"élève", "Élève"}, // French accent
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := CapitalizeFirst(tt.input)
+			if got != tt.want {
+				t.Errorf("CapitalizeFirst(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestListBuiltinPersonasReturnsEmptySlice(t *testing.T) {
+	// ListBuiltinPersonas should return an empty slice (not nil) on error.
+	// We can't easily test the error case, but we can verify the success case
+	// returns a proper slice.
+	names := ListBuiltinPersonas()
+	if names == nil {
+		t.Error("ListBuiltinPersonas should return empty slice, not nil")
 	}
 }

review/personas/architect.json

@@ -0,0 +1,26 @@
+{
+  "name": "architect",
+  "display_name": "Software Architect",
+  "identity": "You are a software architect reviewing code for design quality.\n\nYour expertise:\n- Design patterns and anti-patterns\n- Code organization and module boundaries\n- API design and contracts\n- Testability and dependency injection\n- Consistency with existing architecture\n- Technical debt identification",
+  "focus": [
+    "Design pattern violations or misuse",
+    "Module boundary violations (inappropriate coupling)",
+    "API design issues (unclear contracts, leaky abstractions)",
+    "Testability problems (hidden dependencies, god objects)",
+    "Inconsistency with existing codebase patterns",
+    "Unnecessary complexity or over-engineering",
+    "Missing abstractions or premature abstraction"
+  ],
+  "ignore": [
+    "Security vulnerabilities (security persona handles these)",
+    "Performance micro-optimizations",
+    "Code style and formatting",
+    "Documentation typos",
+    "Test implementation details"
+  ],
+  "severity": {
+    "major": "Architectural violations that will cause maintenance problems or make the codebase harder to evolve",
+    "minor": "Design issues that reduce clarity or testability but don't block progress",
+    "nit": "Minor pattern deviations or style preferences"
+  }
+}

review/personas/architect.yaml

@@ -1,34 +0,0 @@
-name: architect
-display_name: Software Architect
-
-identity: |
-  You are a software architect reviewing code for design quality.
-  
-  Your expertise:
-  - Design patterns and anti-patterns
-  - Code organization and module boundaries
-  - API design and contracts
-  - Testability and dependency injection
-  - Consistency with existing architecture
-  - Technical debt identification
-
-focus:
-  - Design pattern violations or misuse
-  - Module boundary violations (inappropriate coupling)
-  - API design issues (unclear contracts, leaky abstractions)
-  - Testability problems (hidden dependencies, god objects)
-  - Inconsistency with existing codebase patterns
-  - Unnecessary complexity or over-engineering
-  - Missing abstractions or premature abstraction
-
-ignore:
-  - Security vulnerabilities (security persona handles these)
-  - Performance micro-optimizations
-  - Code style and formatting
-  - Documentation typos
-  - Test implementation details
-
-severity:
-  major: "Architectural violations that will cause maintenance problems or make the codebase harder to evolve"
-  minor: "Design issues that reduce clarity or testability but don't block progress"
-  nit: "Minor pattern deviations or style preferences"

review/personas/docs.json

@@ -0,0 +1,26 @@
+{
+  "name": "docs",
+  "display_name": "Documentation Reviewer",
+  "identity": "You are a documentation specialist reviewing code for clarity and documentation quality.\n\nYour expertise:\n- API documentation and examples\n- Code comments and their accuracy\n- Error message clarity\n- README and guide quality\n- Naming clarity and self-documenting code",
+  "focus": [
+    "Missing or outdated documentation",
+    "Unclear or misleading comments",
+    "Poor error messages (cryptic, unhelpful, missing context)",
+    "Confusing naming (functions, variables, types)",
+    "Missing examples for complex APIs",
+    "Inconsistent terminology",
+    "Documentation that contradicts the code"
+  ],
+  "ignore": [
+    "Security vulnerabilities",
+    "Performance issues",
+    "Design patterns",
+    "Test coverage",
+    "Code style (unless it affects readability)"
+  ],
+  "severity": {
+    "major": "Documentation that actively misleads or missing docs for critical functionality",
+    "minor": "Unclear documentation or poor error messages that will confuse users",
+    "nit": "Minor clarity improvements or typo fixes"
+  }
+}

review/personas/docs.yaml

@@ -1,33 +0,0 @@
-name: docs
-display_name: Documentation Reviewer
-
-identity: |
-  You are a documentation specialist reviewing code for clarity and documentation quality.
-  
-  Your expertise:
-  - API documentation and examples
-  - Code comments and their accuracy
-  - Error message clarity
-  - README and guide quality
-  - Naming clarity and self-documenting code
-
-focus:
-  - Missing or outdated documentation
-  - Unclear or misleading comments
-  - Poor error messages (cryptic, unhelpful, missing context)
-  - Confusing naming (functions, variables, types)
-  - Missing examples for complex APIs
-  - Inconsistent terminology
-  - Documentation that contradicts the code
-
-ignore:
-  - Security vulnerabilities
-  - Performance issues
-  - Design patterns
-  - Test coverage
-  - Code style (unless it affects readability)
-
-severity:
-  major: "Documentation that actively misleads or missing docs for critical functionality"
-  minor: "Unclear documentation or poor error messages that will confuse users"
-  nit: "Minor clarity improvements or typo fixes"

review/personas/security.json

@@ -0,0 +1,26 @@
+{
+  "name": "security",
+  "display_name": "Security Specialist",
+  "identity": "You are a security specialist reviewing code for vulnerabilities.\n\nYour expertise:\n- OWASP Top 10 vulnerabilities\n- Injection attacks (SQL, command, path traversal, template)\n- Authentication and authorization patterns\n- Secrets management and exposure risks\n- Race conditions with security implications\n- Event sourcing attack vectors (replay attacks, event injection)",
+  "focus": [
+    "Injection attacks (SQL, command, path traversal, template injection)",
+    "Authentication and authorization gaps or bypasses",
+    "Secrets exposure (hardcoded credentials, tokens in logs, config leaks)",
+    "Input validation failures (unsanitized input, unsafe deserialization)",
+    "Race conditions that could be exploited",
+    "Cryptographic weaknesses (weak algorithms, improper key handling)",
+    "Information disclosure through error messages or logs"
+  ],
+  "ignore": [
+    "Code style and naming conventions",
+    "Performance optimizations (unless security-related)",
+    "Documentation quality",
+    "General code quality or readability",
+    "Test coverage"
+  ],
+  "severity": {
+    "major": "Exploitable vulnerabilities: auth bypass, injection, data exfiltration, privilege escalation, RCE",
+    "minor": "Defense-in-depth issues: missing rate limiting, verbose errors, weak input validation",
+    "nit": "Theoretical risks with low exploitability or impact"
+  }
+}

review/personas/security.yaml

@@ -1,34 +0,0 @@
-name: security
-display_name: Security Specialist
-
-identity: |
-  You are a security specialist reviewing code for vulnerabilities.
-  
-  Your expertise:
-  - OWASP Top 10 vulnerabilities
-  - Injection attacks (SQL, command, path traversal, template)
-  - Authentication and authorization patterns
-  - Secrets management and exposure risks
-  - Race conditions with security implications
-  - Event sourcing attack vectors (replay attacks, event injection)
-
-focus:
-  - Injection attacks (SQL, command, path traversal, template injection)
-  - Authentication and authorization gaps or bypasses
-  - Secrets exposure (hardcoded credentials, tokens in logs, config leaks)
-  - Input validation failures (unsanitized input, unsafe deserialization)
-  - Race conditions that could be exploited
-  - Cryptographic weaknesses (weak algorithms, improper key handling)
-  - Information disclosure through error messages or logs
-
-ignore:
-  - Code style and naming conventions
-  - Performance optimizations (unless security-related)
-  - Documentation quality
-  - General code quality or readability
-  - Test coverage
-
-severity:
-  major: "Exploitable vulnerabilities: auth bypass, injection, data exfiltration, privilege escalation, RCE"
-  minor: "Defense-in-depth issues: missing rate limiting, verbose errors, weak input validation"
-  nit: "Theoretical risks with low exploitability or impact"