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

TODO.md

@@ -31,9 +31,8 @@ P2: security: per-origin rate limiting
 # Completed Steps
 
 - 2026-10-27 the reconciliation pass skips a directory it cannot list and a file
-  whose info it cannot read, and goes on (closes #343). It stopped before its
+  whose info it cannot read, and goes on (closes #343). It returned the error,
-  later checks at a directory it could not list, or at a source or variant file
+  so one such entry stopped every pass before its later checks.
-  whose info it could not read.
     - It logs the warning "skipped unreadable entry in cache directory", with
       the path and the error.
     - A file renamed or removed after its directory was listed gets no warning.

internal/imgcache/eviction_internal_test.go

@@ -819,11 +819,10 @@ func openDirectoryNearPathLimit(t *testing.T, dir string) *os.Root {
 	return root
 }
 
-// makeEntriesTooLongToRead makes a new directory and a new file in the
+// makeEntriesTooLongToRead makes a directory and a file in the directory
-// deepest directory of the chain that openDirectoryNearPathLimit makes
+// that openDirectoryNearPathLimit opens inside dir. Even the root user can
-// inside dir. Even the root user can then neither list the new directory
+// then neither list that directory nor read the file's info. It returns
-// nor read the new file's info. It returns the paths of the new directory
+// their two paths.
-// and the new file.
 func makeEntriesTooLongToRead(t *testing.T, dir string) []string {
 	t.Helper()
 
@@ -848,10 +847,9 @@ func makeEntriesTooLongToRead(t *testing.T, dir string) []string {
 	}
 }
 
-// makeTempFileTooLongToRead makes a temp file in the deepest directory of
+// makeTempFileTooLongToRead makes a temp file in the directory that
-// the chain that openDirectoryNearPathLimit makes inside dir. Even the
+// openDirectoryNearPathLimit opens inside dir. Even the root user then
-// root user then cannot read the temp file's info. It returns the temp
+// cannot read its info. It returns its path.
-// file's path.
 func makeTempFileTooLongToRead(t *testing.T, dir string) string {
 	t.Helper()
 
@@ -866,25 +864,6 @@ func makeTempFileTooLongToRead(t *testing.T, dir string) string {
 	return filepath.Join(deepest.Name(), name)
 }
 
-// assertSkippedEntryWarning checks that logs hold the warning "skipped
-// unreadable entry in cache directory" naming path, with the error
-// ENAMETOOLONG for that path.
-func assertSkippedEntryWarning(t *testing.T, logs, path string) {
-	t.Helper()
-
-	for line := range strings.Lines(logs) {
-		if strings.Contains(line, `"level":"WARN"`) &&
-			strings.Contains(line, `"msg":"skipped unreadable entry in cache directory"`) &&
-			strings.Contains(line, `"path":"`+path+`"`) &&
-			strings.Contains(line, path+": "+syscall.ENAMETOOLONG.Error()) {
-			return
-		}
-	}
-
-	t.Errorf("no warning %q names %s with the error %q",
-		"skipped unreadable entry in cache directory", path, syscall.ENAMETOOLONG)
-}
-
 // TestReconciliationGoesOnPastEntriesItCannotRead puts, in each storage
 // directory, a directory the pass cannot list and a file whose info it
 // cannot read. The pass walks each directory in name order, so it reaches
@@ -936,7 +915,11 @@ func TestReconciliationGoesOnPastEntriesItCannotRead(t *testing.T) {
 	logs := reconcileAsAtStartup(t, cache)
 
 	for _, path := range unreadable {
-		assertSkippedEntryWarning(t, logs, path)
+		assertWarningNames(t, logs, path)
+
+		if !strings.Contains(logs, path+": "+syscall.ENAMETOOLONG.Error()) {
+			t.Errorf("no log line gives the error reading %s", path)
+		}
 	}
 
 	rowQuery := `SELECT COUNT(*) FROM variant_content WHERE cache_key = ?`
@@ -965,11 +948,11 @@ func TestReconciliationGoesOnPastEntriesItCannotRead(t *testing.T) {
 	}
 }
 
-// TestReconciliationWarnsOfTempFilesWhoseInfoItCannotRead puts, in each
+// TestReconciliationWarnsOfTempFilesItCannotRead puts, in each storage
-// storage directory, a temp file whose info the pass cannot read. The
+// directory, a temp file whose info the pass cannot read. The pass must
-// pass must log a warning naming each one's path and the error, as it
+// log a warning naming each one's path and the error, as it does for any
-// does for any other file whose info it cannot read.
+// other file whose info it cannot read.
-func TestReconciliationWarnsOfTempFilesWhoseInfoItCannotRead(t *testing.T) {
+func TestReconciliationWarnsOfTempFilesItCannotRead(t *testing.T) {
 	t.Parallel()
 
 	cache, _ := newEvictionTestCache(t, 1<<30)
@@ -982,7 +965,11 @@ func TestReconciliationWarnsOfTempFilesWhoseInfoItCannotRead(t *testing.T) {
 	logs := reconcileAsAtStartup(t, cache)
 
 	for _, path := range unreadable {
-		assertSkippedEntryWarning(t, logs, path)
+		assertWarningNames(t, logs, path)
+
+		if !strings.Contains(logs, path+": "+syscall.ENAMETOOLONG.Error()) {
+			t.Errorf("no log line gives the error reading %s", path)
+		}
 	}
 }