Go on past cache entries the reconciliation pass cannot read (closes #343)

The walk of each storage directory returned the error of an entry it
could not read. The pass then stopped before its later checks, and the
same entry stopped every later pass. Now reconcileFiles skips a
directory it cannot list and a file whose info it cannot read, temp
files included. It logs a warning naming the path and the error, and the
walk goes on. It reads each file's info once, before the temp-file
check, and hands it to sweepStaleTempFile, reconcileVariantFile or
reconcileSourceFile. A file renamed or removed after its directory was
listed is skipped with no warning. A cancelled context still stops the
walk with its error. README.md says so under Storage.

Model: opus-5-5

internal/imgcache/eviction.go

@@ -515,12 +515,15 @@ func (c *Cache) reconcileAccounting(ctx context.Context) error {
 }
 
 // reconcileFiles walks baseDir, one of the cache's storage directories,
-// sweeping stale temp files and passing each other file, with its name, to
-// reconcileFile. Once ctx is cancelled it stops at the next file and
-// returns ctx's error.
+// sweeping stale temp files and passing each other file, with its info and
+// name, to reconcileFile. It skips a directory it cannot list and a file
+// whose info it cannot read, so one such entry does not stop the pass. It
+// logs a warning naming the path and the error. A file renamed or removed
+// after its directory was listed is skipped with no warning. Once ctx is
+// cancelled it stops at the next file and returns ctx's error.
 func (c *Cache) reconcileFiles(
 	ctx context.Context, baseDir string,
-	reconcileFile func(path string, entry fs.DirEntry, name string) error,
+	reconcileFile func(path string, info fs.FileInfo, name string) error,
 ) error {
 	return filepath.WalkDir(
 		baseDir,
@@ -529,19 +532,38 @@ func (c *Cache) reconcileFiles(
 				return ctx.Err()
 			}
 
-			if err != nil || entry.IsDir() {
-				return err
+			if err != nil {
+				c.log.Warn("skipped unreadable entry in cache directory",
+					"path", path, "error", err)
+
+				return nil
+			}
+
+			if entry.IsDir() {
+				return nil
+			}
+
+			info, err := entry.Info()
+			if errors.Is(err, fs.ErrNotExist) {
+				return nil
+			}
+
+			if err != nil {
+				c.log.Warn("skipped unreadable entry in cache directory",
+					"path", path, "error", err)
+
+				return nil
 			}
 
 			name := entry.Name()
 
 			if strings.HasPrefix(name, tempFilePrefix) {
-				c.sweepStaleTempFile(path, entry)
+				c.sweepStaleTempFile(path, info)
 
 				return nil
 			}
 
-			return reconcileFile(path, entry, name)
+			return reconcileFile(path, info, name)
 		},
 	)
 }
@@ -551,8 +573,8 @@ func (c *Cache) reconcileFiles(
 // and sweeping stale temp files.
 func (c *Cache) reconcileVariantFiles(ctx context.Context) error {
 	return c.reconcileFiles(ctx, c.variants.baseDir,
-		func(path string, entry fs.DirEntry, name string) error {
-			return c.reconcileVariantFile(ctx, path, entry, imagerequest.VariantKey(name))
+		func(path string, info fs.FileInfo, name string) error {
+			return c.reconcileVariantFile(ctx, path, info, imagerequest.VariantKey(name))
 		})
 }
 
@@ -562,16 +584,11 @@ func (c *Cache) reconcileVariantFiles(ctx context.Context) error {
 // crash or a restored snapshot can leave it, is removed with its row and
 // a warning naming it, so the variant is converted again.
 func (c *Cache) reconcileVariantFile(
-	ctx context.Context, path string, entry fs.DirEntry, cacheKey imagerequest.VariantKey,
+	ctx context.Context, path string, info fs.FileInfo, cacheKey imagerequest.VariantKey,
 ) error {
-	info, err := entry.Info()
-	if err != nil {
-		return fmt.Errorf("failed to stat variant file: %w", err)
-	}
-
 	var recordedSize int64
 
-	err = c.db.QueryRowContext(ctx,
+	err := c.db.QueryRowContext(ctx,
 		`SELECT size_bytes FROM variant_content WHERE cache_key = ?`, string(cacheKey),
 	).Scan(&recordedSize)
 
@@ -714,8 +731,8 @@ func queryStringColumn[T ~string](
 // and sweeping stale temp files.
 func (c *Cache) reconcileSourceFiles(ctx context.Context) error {
 	return c.reconcileFiles(ctx, c.srcContent.baseDir,
-		func(path string, entry fs.DirEntry, name string) error {
-			return c.reconcileSourceFile(ctx, path, entry, imagerequest.SourceKey(name))
+		func(path string, info fs.FileInfo, name string) error {
+			return c.reconcileSourceFile(ctx, path, info, imagerequest.SourceKey(name))
 		})
 }
 
@@ -726,16 +743,11 @@ func (c *Cache) reconcileSourceFiles(ctx context.Context) error {
 // is removed with its row and a warning naming it, so the source is
 // fetched again.
 func (c *Cache) reconcileSourceFile(
-	ctx context.Context, path string, entry fs.DirEntry, key imagerequest.SourceKey,
+	ctx context.Context, path string, info fs.FileInfo, key imagerequest.SourceKey,
 ) error {
-	info, err := entry.Info()
-	if err != nil {
-		return fmt.Errorf("failed to stat source content file: %w", err)
-	}
-
 	var recordedSize int64
 
-	err = c.db.QueryRowContext(ctx,
+	err := c.db.QueryRowContext(ctx,
 		`SELECT size_bytes FROM source_content WHERE source_key = ?`,
 		string(key),
 	).Scan(&recordedSize)
@@ -900,17 +912,12 @@ func (c *Cache) correctUsageTotal(
 
 // sweepStaleTempFile removes a temp file left behind by a crashed
 // write once it is old enough that no in-flight store can own it.
-func (c *Cache) sweepStaleTempFile(path string, entry fs.DirEntry) {
-	info, err := entry.Info()
-	if err != nil {
-		return
-	}
-
+func (c *Cache) sweepStaleTempFile(path string, info fs.FileInfo) {
 	if time.Since(info.ModTime()) < staleTempFileAge {
 		return
 	}
 
-	err = os.Remove(path)
+	err := os.Remove(path)
 	if err != nil && !os.IsNotExist(err) {
 		c.log.Warn("failed to remove stale temp file", "path", path, "error", err)