Remediate all lint findings under the canonical golangci-lint config

Fix every finding surfaced by the canonical .golangci.yml with
golangci-lint v2.12.2 (refs #61), behavior-preserving throughout:

- err113: dynamic errors replaced with package-level sentinels and %w
  wrapping; direct comparisons converted to errors.Is
- goprintffuncname: printf-style helpers renamed with an f suffix
  (ui.Writer message methods, cli.ReportErrorf, database.Fatalf,
  vaultik stdoutf) and all call sites updated
- revive: stuttering type names renamed (blob.Handler, blob.WithReader,
  blob.ChunkPosition, storage.URL, storage.Info), doc comments added,
  unused parameters blanked, package comments added
- contextcheck/noctx: ctx threaded through blob.Packer
  (AddChunk/Flush/FinalizeBlob/PackChunks) and scanner call sites;
  context-aware exec and sql variants used
- funlen/cyclop/gocognit/nestif/dupl: oversized or duplicated
  functions split into focused helpers across production and test code
- paralleltest/tparallel/thelper/usetesting/testpackage: tests
  parallelized where safe (global log.Initialize kept in the serial
  phase), helpers marked, t.TempDir adopted, external test packages
  where only exported API is used
- gosec: integer conversions clamped or justified, header timeouts
  added, remaining findings suppressed with per-site justifications
- mnd/goconst/lll/wsl_v5/nlreturn/noinlineerr/errcheck and other
  mechanical findings fixed directly

Remove the deprecated log.LogOptions alias (callers migrated to
log.Options). make check is green.

internal/chunker/chunker.go

@@ -1,3 +1,6 @@
+// Package chunker splits input data into content-defined chunks using the
+// FastCDC algorithm so that identical data sequences produce identical
+// chunks regardless of their position in the file.
 package chunker
 
 import (
@@ -9,9 +12,10 @@ import (
 	"os"
 )
 
-// Chunk represents a single chunk of data produced by the content-defined chunking algorithm.
-// Each chunk is identified by its SHA256 hash and contains the raw data along with
-// its position and size information from the original file.
+// Chunk represents a single chunk of data produced by the content-defined
+// chunking algorithm. Each chunk is identified by its SHA256 hash and
+// contains the raw data along with its position and size information from
+// the original file.
 type Chunk struct {
 	Hash   string // Content hash of the chunk
 	Data   []byte // Chunk data
@@ -29,6 +33,10 @@ type Chunker struct {
 	maxChunkSize int
 }
 
+// chunkSizeSpread is the FastCDC-recommended factor between the average
+// chunk size and the minimum (avg/spread) and maximum (avg*spread) sizes.
+const chunkSizeSpread = 4
+
 // NewChunker creates a new chunker with the specified average chunk size.
 // The actual chunk sizes will vary between avgChunkSize/4 and avgChunkSize*4
 // as recommended by the FastCDC algorithm. Typical values for avgChunkSize
@@ -37,17 +45,19 @@ func NewChunker(avgChunkSize int64) *Chunker {
 	// FastCDC recommends min = avg/4 and max = avg*4
 	return &Chunker{
 		avgChunkSize: int(avgChunkSize),
-		minChunkSize: int(avgChunkSize / 4),
-		maxChunkSize: int(avgChunkSize * 4),
+		minChunkSize: int(avgChunkSize / chunkSizeSpread),
+		maxChunkSize: int(avgChunkSize * chunkSizeSpread),
 	}
 }
 
-// ChunkReader splits the reader into content-defined chunks and returns all chunks at once.
-// This method loads all chunk data into memory, so it should only be used for
-// reasonably sized inputs. For large files or streams, use ChunkReaderStreaming instead.
+// ChunkReader splits the reader into content-defined chunks and returns all
+// chunks at once. This method loads all chunk data into memory, so it should
+// only be used for reasonably sized inputs. For large files or streams, use
+// ChunkReaderStreaming instead.
 // Returns an error if chunking fails or if reading from the input fails.
 func (c *Chunker) ChunkReader(r io.Reader) ([]Chunk, error) {
-	chunker := AcquireReusableChunker(r, c.minChunkSize, c.avgChunkSize, c.maxChunkSize)
+	chunker := AcquireReusableChunker(
+		r, c.minChunkSize, c.avgChunkSize, c.maxChunkSize)
 	defer chunker.Release()
 
 	var chunks []Chunk
@@ -86,21 +96,26 @@ func (c *Chunker) ChunkReader(r io.Reader) ([]Chunk, error) {
 
 // ChunkCallback is a function called for each chunk as it's processed.
 // The callback receives a Chunk containing the hash, data, offset, and size.
-// If the callback returns an error, chunk processing stops and the error is propagated.
+// If the callback returns an error, chunk processing stops and the error is
+// propagated.
 type ChunkCallback func(chunk Chunk) error
 
-// ChunkReaderStreaming splits the reader into chunks and calls the callback for each chunk.
-// This is the preferred method for processing large files or streams as it doesn't
-// accumulate all chunks in memory. The callback is invoked for each chunk as it's
-// produced, allowing for streaming processing and immediate storage or transmission.
-// Returns the SHA256 hash of the entire file content and an error if chunking fails,
-// reading fails, or if the callback returns an error.
-func (c *Chunker) ChunkReaderStreaming(r io.Reader, callback ChunkCallback) (string, error) {
+// ChunkReaderStreaming splits the reader into chunks and calls the callback
+// for each chunk. This is the preferred method for processing large files or
+// streams as it doesn't accumulate all chunks in memory. The callback is
+// invoked for each chunk as it's produced, allowing for streaming processing
+// and immediate storage or transmission.
+// Returns the SHA256 hash of the entire file content and an error if
+// chunking fails, reading fails, or if the callback returns an error.
+func (c *Chunker) ChunkReaderStreaming(
+	r io.Reader, callback ChunkCallback,
+) (string, error) {
 	// Create a tee reader to calculate full file hash while chunking
 	fileHasher := sha256.New()
 	teeReader := io.TeeReader(r, fileHasher)
 
-	chunker := AcquireReusableChunker(teeReader, c.minChunkSize, c.avgChunkSize, c.maxChunkSize)
+	chunker := AcquireReusableChunker(
+		teeReader, c.minChunkSize, c.avgChunkSize, c.maxChunkSize)
 	defer chunker.Release()
 
 	offset := int64(0)
@@ -118,15 +133,17 @@ func (c *Chunker) ChunkReaderStreaming(r io.Reader, callback ChunkCallback) (str
 		// Calculate chunk hash
 		hash := sha256.Sum256(chunk.Data)
 
-		// Pass the data directly - caller must process it before we call Next() again
-		// (chunker reuses its internal buffer, but since we process synchronously
-		// and completely before continuing, no copy is needed)
-		if err := callback(Chunk{
+		// Pass the data directly - caller must process it before we call
+		// Next() again (chunker reuses its internal buffer, but since we
+		// process synchronously and completely before continuing, no copy
+		// is needed)
+		err = callback(Chunk{
 			Hash:   hex.EncodeToString(hash[:]),
 			Data:   chunk.Data,
 			Offset: offset,
 			Size:   int64(len(chunk.Data)),
-		}); err != nil {
+		})
+		if err != nil {
 			return "", fmt.Errorf("callback error: %w", err)
 		}
 
@@ -142,7 +159,7 @@ func (c *Chunker) ChunkReaderStreaming(r io.Reader, callback ChunkCallback) (str
 // For large files, consider using ChunkReaderStreaming with a file handle instead.
 // Returns an error if the file cannot be opened or if chunking fails.
 func (c *Chunker) ChunkFile(path string) ([]Chunk, error) {
-	file, err := os.Open(path)
+	file, err := os.Open(path) //nolint:gosec // G304: path is caller-supplied by design
 	if err != nil {
 		return nil, fmt.Errorf("opening file: %w", err)
 	}