Fix all linter errors

- Add explicit error ignoring with _ = for Close/Remove calls
- Rename WriteTo to Write to avoid io.WriterTo interface conflict
- Fix errcheck warnings in fetch, freshen, gen, mfer, checker,
  deserialize, serialize, and output files

internal/checker/checker.go

@@ -218,7 +218,7 @@ func (c *Checker) checkFile(entry *mfer.MFFilePath, checkedBytes *int64) Result
 	if err != nil {
 		return Result{Path: entry.Path, Status: StatusError, Message: err.Error()}
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 
 	h := sha256.New()
 	n, err := io.Copy(h, f)

internal/cli/fetch.go

@@ -48,7 +48,7 @@ func (mfa *CLIApp) fetchManifestOperation(ctx *cli.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to fetch manifest: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("failed to fetch manifest: HTTP %d", resp.StatusCode)
@@ -283,7 +283,7 @@ func downloadFile(fileURL, localPath string, entry *mfer.MFFilePath, progress ch
 	if err != nil {
 		return err
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("HTTP %d", resp.StatusCode)
@@ -322,24 +322,24 @@ func downloadFile(fileURL, localPath string, entry *mfer.MFFilePath, progress ch
 
 	// If copy failed, clean up temp file and return error
 	if copyErr != nil {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return copyErr
 	}
 	if closeErr != nil {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return closeErr
 	}
 
 	// Verify size
 	if written != expectedSize {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return fmt.Errorf("size mismatch: expected %d bytes, got %d", expectedSize, written)
 	}
 
 	// Encode computed hash as multihash
 	computed, err := multihash.Encode(h.Sum(nil), multihash.SHA2_256)
 	if err != nil {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return fmt.Errorf("failed to encode hash: %w", err)
 	}
 
@@ -352,13 +352,13 @@ func downloadFile(fileURL, localPath string, entry *mfer.MFFilePath, progress ch
 		}
 	}
 	if !hashMatch {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return fmt.Errorf("hash mismatch")
 	}
 
 	// Rename temp file to final path
 	if err := os.Rename(tmpPath, localPath); err != nil {
-		os.Remove(tmpPath)
+		_ = os.Remove(tmpPath)
 		return fmt.Errorf("failed to rename temp file: %w", err)
 	}
 

internal/cli/fetch_test.go

@@ -127,7 +127,7 @@ func TestFetchFromHTTP(t *testing.T) {
 		path := r.URL.Path
 		if path == "/index.mf" {
 			w.Header().Set("Content-Type", "application/octet-stream")
-			w.Write(manifestData)
+			_, _ = w.Write(manifestData)
 			return
 		}
 
@@ -143,20 +143,20 @@ func TestFetchFromHTTP(t *testing.T) {
 		}
 
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(content)
+		_, _ = w.Write(content)
 	}))
 	defer server.Close()
 
 	// Create destination directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	// Change to dest directory for the test
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Parse the manifest to get file entries
 	manifest, err := mfer.NewManifestFromReader(bytes.NewReader(manifestData))
@@ -217,19 +217,19 @@ func TestFetchHashMismatch(t *testing.T) {
 	tamperedContent := []byte("Tampered content!")
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(tamperedContent)
+		_, _ = w.Write(tamperedContent)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-hash-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Try to download - should fail with hash mismatch
 	err = downloadFile(server.URL+"/file.txt", "file.txt", files[0], nil)
@@ -269,19 +269,19 @@ func TestFetchSizeMismatch(t *testing.T) {
 	wrongSizeContent := []byte("Short")
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/octet-stream")
-		w.Write(wrongSizeContent)
+		_, _ = w.Write(wrongSizeContent)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-size-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Try to download - should fail with size mismatch
 	err = downloadFile(server.URL+"/file.txt", "file.txt", files[0], nil)
@@ -320,19 +320,19 @@ func TestFetchProgress(t *testing.T) {
 		w.Header().Set("Content-Length", "102400")
 		// Write in chunks to allow progress reporting
 		reader := bytes.NewReader(content)
-		io.Copy(w, reader)
+		_, _ = io.Copy(w, reader)
 	}))
 	defer server.Close()
 
 	// Create temp directory
 	destDir, err := os.MkdirTemp("", "mfer-fetch-progress-test-*")
 	require.NoError(t, err)
-	defer os.RemoveAll(destDir)
+	defer func() { _ = os.RemoveAll(destDir) }()
 
 	origDir, err := os.Getwd()
 	require.NoError(t, err)
 	require.NoError(t, os.Chdir(destDir))
-	defer os.Chdir(origDir)
+	defer func() { _ = os.Chdir(origDir) }()
 
 	// Set up progress channel and collect updates
 	progress := make(chan DownloadProgress, 100)

internal/cli/freshen.go

@@ -258,7 +258,7 @@ func (mfa *CLIApp) freshenManifestOperation(ctx *cli.Context) error {
 					}
 				}
 			})
-			f.Close()
+			_ = f.Close()
 
 			if err != nil {
 				return fmt.Errorf("failed to hash %s: %w", e.path, err)
@@ -287,15 +287,15 @@ func (mfa *CLIApp) freshenManifestOperation(ctx *cli.Context) error {
 	}
 
 	err = builder.Build(outFile)
-	outFile.Close()
+	_ = outFile.Close()
 	if err != nil {
-		mfa.Fs.Remove(tmpPath)
+		_ = mfa.Fs.Remove(tmpPath)
 		return fmt.Errorf("failed to write manifest: %w", err)
 	}
 
 	// Rename temp to final
 	if err := mfa.Fs.Rename(tmpPath, manifestPath); err != nil {
-		mfa.Fs.Remove(tmpPath)
+		_ = mfa.Fs.Remove(tmpPath)
 		return fmt.Errorf("failed to rename manifest: %w", err)
 	}
 

internal/cli/gen.go

@@ -76,7 +76,7 @@ func (mfa *CLIApp) generateManifestOperation(ctx *cli.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to create output file: %w", err)
 	}
-	defer outFile.Close()
+	defer func() { _ = outFile.Close() }()
 
 	// Phase 2: Scan - read file contents and generate manifest
 	var scanProgress chan scanner.ScanStatus

internal/cli/mfer.go

@@ -41,7 +41,7 @@ const banner = `
     \__\/         \__\/       \__\/         \__\/`
 
 func (mfa *CLIApp) printBanner() {
-	fmt.Fprintln(mfa.Stdout, banner)
+	_, _ = fmt.Fprintln(mfa.Stdout, banner)
 }
 
 // VersionString returns the version and git revision formatted for display.
@@ -201,7 +201,7 @@ func (mfa *CLIApp) run(args []string) {
 				Name:  "version",
 				Usage: "Show version",
 				Action: func(c *cli.Context) error {
-					fmt.Fprintln(mfa.Stdout, mfa.VersionString())
+					_, _ = fmt.Fprintln(mfa.Stdout, mfa.VersionString())
 					return nil
 				},
 			},

mfer/deserialize.go

@@ -26,7 +26,7 @@ func (m *manifest) deserializeInner() error {
 	if err != nil {
 		return err
 	}
-	defer gzr.Close()
+	defer func() { _ = gzr.Close() }()
 
 	dat, err := io.ReadAll(gzr)
 	if err != nil {
@@ -99,7 +99,7 @@ func NewManifestFromFile(fs afero.Fs, path string) (*manifest, error) {
 	if err != nil {
 		return nil, err
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 	return NewManifestFromReader(f)
 }
 

mfer/output.go

@@ -12,12 +12,12 @@ func (m *manifest) WriteToFile(path string) error {
 	if err != nil {
 		return err
 	}
-	defer f.Close()
+	defer func() { _ = f.Close() }()
 
-	return m.WriteTo(f)
+	return m.Write(f)
 }
 
-func (m *manifest) WriteTo(output io.Writer) error {
+func (m *manifest) Write(output io.Writer) error {
 	if m.pbOuter == nil {
 		err := m.generate()
 		if err != nil {

mfer/serialize.go

@@ -65,7 +65,7 @@ func (m *manifest) generateOuter() error {
 		return err
 	}
 
-	gzw.Close()
+	_ = gzw.Close()
 
 	o := &MFFileOuter{
 		InnerMessage:    idc.Bytes(),