NewChecker takes CheckerOptions instead of positional arguments (closes #78)

NewChecker now takes *CheckerOptions (ManifestPath, BasePath, Fs), named
like ScannerOptions. A nil Fs still means the OS filesystem, as before and
as in ScannerOptions; nil options or an empty path return an error naming
the missing path.

Audit of the other exported constructors in mfer: NewManifestFromFile took
a filesystem and a path positionally; it now takes
*ManifestFromFileOptions (Path, Fs) with the same nil and empty rules.
NewBuilder and NewScanner take no arguments, NewScannerWithOptions already
takes options, and NewManifestFromReader takes one reader, which the style
guide exempts; these are unchanged.

Model: opus-5-5

internal/cli/check.go

@@ -298,7 +298,11 @@ func (mfa *CLIApp) checkManifestOperation(ctx *cli.Context) error {
 	log.Infof("checking manifest %s with base %s", manifestPath, basePath)
 
 	// Create checker
-	chk, err := mfer.NewChecker(manifestPath, basePath, mfa.Fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: manifestPath,
+		BasePath:     basePath,
+		Fs:           mfa.Fs,
+	})
 	if err != nil {
 		return fmt.Errorf("failed to load manifest: %w", err)
 	}

internal/cli/entry_test.go

@@ -504,7 +504,10 @@ func TestGenerateExcludesDotfilesByDefault(t *testing.T) {
 	assert.True(t, exists)
 
 	// Verify manifest only has 1 file (the non-dotfile)
-	manifest, err := mfer.NewManifestFromFile(fs, testMF)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: testMF,
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 1)
 	assert.Equal(t, "file1.txt", manifest.Files()[0].GetPath())
@@ -528,7 +531,10 @@ func TestGenerateWithIncludeDotfiles(t *testing.T) {
 	require.Equal(t, 0, exitCode)
 
 	// Verify manifest has 2 files (including dotfile)
-	manifest, err := mfer.NewManifestFromFile(fs, testMF)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: testMF,
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)
 }

internal/cli/errmsg_test.go

@@ -61,7 +61,11 @@ func unsignedChecker(t *testing.T) *mfer.Checker {
 	require.NoError(t, s.ToManifest(context.Background(), &buf, nil))
 	require.NoError(t, afero.WriteFile(fs, "/d/index.mf", buf.Bytes(), 0o644))
 
-	chk, err := mfer.NewChecker("/d/index.mf", "/d", fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: "/d/index.mf",
+		BasePath:     "/d",
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 	require.False(t, chk.IsSigned())
 
@@ -167,7 +171,11 @@ func signedChecker(t *testing.T) *mfer.Checker {
 	fs := afero.NewMemMapFs()
 	require.NoError(t, afero.WriteFile(fs, "/index.mf", buf.Bytes(), 0o644))
 
-	chk, err := mfer.NewChecker("/index.mf", "/", fs)
+	chk, err := mfer.NewChecker(&mfer.CheckerOptions{
+		ManifestPath: "/index.mf",
+		BasePath:     "/",
+		Fs:           fs,
+	})
 	require.NoError(t, err)
 	require.True(t, chk.IsSigned())
 

internal/cli/freshen.go

@@ -445,7 +445,10 @@ func (mfa *CLIApp) loadExistingEntries(
 	log.Infof("loading manifest from %s", manifestPath)
 
 	// Load existing manifest
-	manifest, err := mfer.NewManifestFromFile(mfa.Fs, manifestPath)
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: manifestPath,
+		Fs:   mfa.Fs,
+	})
 	if err != nil {
 		return nil, fmt.Errorf("failed to load manifest: %w", err)
 	}

internal/cli/freshen_test.go

@@ -58,7 +58,10 @@ func TestFreshenUnchanged(t *testing.T) {
 	setupFreshenDir(t, fs)
 
 	// Parse manifest to verify
-	manifest, err := mfer.NewManifestFromFile(fs, "/testdir/.index.mf")
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: "/testdir/.index.mf",
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)
 }
@@ -70,7 +73,10 @@ func TestFreshenWithChanges(t *testing.T) {
 	setupFreshenDir(t, fs)
 
 	// Verify initial manifest has 2 files
-	manifest, err := mfer.NewManifestFromFile(fs, "/testdir/.index.mf")
+	manifest, err := mfer.NewManifestFromFile(&mfer.ManifestFromFileOptions{
+		Path: "/testdir/.index.mf",
+		Fs:   fs,
+	})
 	require.NoError(t, err)
 	assert.Len(t, manifest.Files(), 2)