feat(gradle): release v1.6.0 — Gradle build file version bump

Add internal/gradle package with ReadVersion and WriteVersion for
build.gradle (Groovy DSL, single-quoted) and build.gradle.kts (Kotlin
DSL, double-quoted). Quote style is preserved on write. regexp.QuoteMeta
ensures version strings with dots or special characters are safe.

Config follows the established multi-value pattern:
- gradle.build_file: single path (opt-in, no default)
- gradle.build_files: list for multi-module projects (overrides build_file)
- --gradle flag overrides build_file and clears build_files

100% per-package statement coverage maintained across all 13 packages;
FuzzReadVersion and FuzzWriteVersion added per fuzzing guidelines.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/gradle/gradle_test.go

@@ -0,0 +1,180 @@
+package gradle
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const gradleGroovy = `plugins {
+    id 'java'
+}
+
+group = 'com.example'
+version = '1.2.3'
+description = 'My project'
+`
+
+const gradleKotlin = `plugins {
+    kotlin("jvm") version "1.9.0"
+}
+
+group = "com.example"
+version = "1.2.3"
+description = "My project"
+`
+
+func writeGradle(t *testing.T, content string) string {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "build.gradle")
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+// ── ReadVersion ──────────────────────────────────────────────────────────────
+
+func TestReadVersionGroovy(t *testing.T) {
+	got, err := ReadVersion(writeGradle(t, gradleGroovy))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionKotlin(t *testing.T) {
+	got, err := ReadVersion(writeGradle(t, gradleKotlin))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.2.3" {
+		t.Errorf("got %q, want 1.2.3", got)
+	}
+}
+
+func TestReadVersionNoSpaces(t *testing.T) {
+	got, err := ReadVersion(writeGradle(t, `version="1.0.0"`))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "1.0.0" {
+		t.Errorf("got %q, want 1.0.0", got)
+	}
+}
+
+func TestReadVersionMissingFile(t *testing.T) {
+	_, err := ReadVersion(filepath.Join(t.TempDir(), "build.gradle"))
+	if err == nil {
+		t.Error("expected error for missing file")
+	}
+}
+
+func TestReadVersionNoVersionField(t *testing.T) {
+	_, err := ReadVersion(writeGradle(t, `group = "com.example"`))
+	if err == nil {
+		t.Error("expected error when no version assignment is present")
+	}
+}
+
+// ── WriteVersion ─────────────────────────────────────────────────────────────
+
+func TestWriteVersionKotlin(t *testing.T) {
+	path := writeGradle(t, gradleKotlin)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(path)
+	if !strings.Contains(string(data), `version = "1.2.4"`) {
+		t.Errorf("expected updated version; got:\n%s", data)
+	}
+	// plugin version declaration must not be touched
+	if !strings.Contains(string(data), `kotlin("jvm") version "1.9.0"`) {
+		t.Error("plugin version was incorrectly modified")
+	}
+}
+
+func TestWriteVersionGroovy(t *testing.T) {
+	path := writeGradle(t, gradleGroovy)
+	if err := WriteVersion(path, "1.2.3", "1.2.4"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	data, _ := os.ReadFile(path)
+	if !strings.Contains(string(data), `version = '1.2.4'`) {
+		t.Errorf("expected updated version with single quotes; got:\n%s", data)
+	}
+}
+
+func TestWriteVersionMissingFile(t *testing.T) {
+	err := WriteVersion(filepath.Join(t.TempDir(), "build.gradle"), "1.0.0", "1.0.1")
+	if err == nil {
+		t.Error("expected error for missing file")
+	}
+}
+
+func TestWriteVersionNotFound(t *testing.T) {
+	path := writeGradle(t, gradleKotlin)
+	err := WriteVersion(path, "9.9.9", "9.9.10")
+	if err == nil {
+		t.Error("expected error when old version not found in file")
+	}
+}
+
+func TestWriteVersionReadOnly(t *testing.T) {
+	path := writeGradle(t, gradleKotlin)
+	os.Chmod(path, 0444)
+	defer os.Chmod(path, 0644)
+	err := WriteVersion(path, "1.2.3", "1.2.4")
+	if err == nil {
+		t.Error("expected error writing to read-only file")
+	}
+}
+
+// ── replaceVersion ────────────────────────────────────────────────────────────
+
+func TestReplaceVersionNotFound(t *testing.T) {
+	content := `group = "com.example"`
+	got, ok := replaceVersion(content, "1.0.0", "1.0.1")
+	if ok {
+		t.Error("expected ok=false when version not present")
+	}
+	if got != content {
+		t.Error("content should be unchanged when not found")
+	}
+}
+
+// ── fuzz ──────────────────────────────────────────────────────────────────────
+
+// FuzzReadVersion verifies ReadVersion never panics on arbitrary file content.
+func FuzzReadVersion(f *testing.F) {
+	f.Add(gradleGroovy)
+	f.Add(gradleKotlin)
+	f.Add(`version="1.0.0"`)
+	f.Add(`group = "com.example"`)
+	f.Add("")
+	f.Add("\x00\xff")
+
+	f.Fuzz(func(t *testing.T, content string) {
+		path := filepath.Join(t.TempDir(), "build.gradle")
+		os.WriteFile(path, []byte(content), 0644) //nolint:errcheck
+		ReadVersion(path)                          //nolint:errcheck
+	})
+}
+
+// FuzzWriteVersion verifies WriteVersion never panics on arbitrary content or version strings.
+func FuzzWriteVersion(f *testing.F) {
+	f.Add(gradleGroovy, "1.2.3", "1.2.4")
+	f.Add(gradleKotlin, "1.2.3", "1.2.4")
+	f.Add(`version="1.0.0"`, "1.0.0", "1.0.1")
+	f.Add("", "1.0.0", "1.0.1")
+	f.Add(`version = "1.0.0"`, "", "1.0.1")
+
+	f.Fuzz(func(t *testing.T, content, oldVersion, newVersion string) {
+		path := filepath.Join(t.TempDir(), "build.gradle")
+		os.WriteFile(path, []byte(content), 0644)  //nolint:errcheck
+		WriteVersion(path, oldVersion, newVersion)  //nolint:errcheck
+	})
+}