Store a source the way a variant is stored, one row and one file per source URL (closes #308)

A source is now one source_content row and one file named by its
SourceKey, the SHA-256 of its host, path and query, made as the variant
key is. A store writes the file, then upserts the row, and removes the
file when the row cannot be written; an eviction deletes the row, then
the file, with no lock. source_metadata, the JSON files under
cache/metadata/, MetadataStorage, the content lock, the eviction
transaction and its test hook are gone, as is the reconciliation pass
that dropped a source row whose file is missing. Two source URLs
serving the same bytes store them twice.

Model: opus-5-5

internal/imgcache/partial_cache_files_internal_test.go

@@ -2,8 +2,6 @@ package imgcache
 
 import (
 	"bytes"
-	"crypto/sha256"
-	"encoding/hex"
 	"io"
 	"log/slog"
 	"os"
@@ -67,12 +65,12 @@ func cachedSourcePath(
 ) string {
 	t.Helper()
 
-	contentHash, _, err := svc.cache.LookupSource(t.Context(), req)
-	if err != nil || contentHash == "" {
-		t.Fatalf("LookupSource() = %q, %v; want the cached source", contentHash, err)
+	sourceKey, _, err := svc.cache.LookupSource(t.Context(), req)
+	if err != nil || sourceKey == "" {
+		t.Fatalf("LookupSource() = %q, %v; want the cached source", sourceKey, err)
 	}
 
-	return svc.cache.srcContent.hashToPath(contentHash)
+	return svc.cache.srcContent.keyToPath(sourceKey)
 }
 
 // reconcileAsAtStartup runs the cache's reconciliation pass, as pixa does
@@ -316,10 +314,10 @@ func TestVariantStorage_StoreReplacesMetaFile(t *testing.T) {
 	}
 }
 
-// TestContentStorage_StoreHashedReplacesFileOfAnotherSize checks that a
-// store over a file of another size at the content's path, such as a
+// TestContentStorage_StoreReplacesFileOfAnotherSize checks that a
+// store over a file of another size at the source's path, such as a
 // partial file a crash left, replaces it with the content.
-func TestContentStorage_StoreHashedReplacesFileOfAnotherSize(t *testing.T) {
+func TestContentStorage_StoreReplacesFileOfAnotherSize(t *testing.T) {
 	t.Parallel()
 
 	storage, err := NewContentStorage(t.TempDir())
@@ -328,13 +326,12 @@ func TestContentStorage_StoreHashedReplacesFileOfAnotherSize(t *testing.T) {
 	}
 
 	content := []byte("the whole source image")
-	sum := sha256.Sum256(content)
-	hash := ContentHash(hex.EncodeToString(sum[:]))
-	path := storage.hashToPath(hash)
+	key := imagerequest.Source{Host: testHostCDN, Path: testPathCat}.Key()
+	path := storage.keyToPath(key)
 
 	err = os.MkdirAll(filepath.Dir(path), StorageDirPerm)
 	if err != nil {
-		t.Fatalf("creating the content's directory: %v", err)
+		t.Fatalf("creating the source's directory: %v", err)
 	}
 
 	err = os.WriteFile(path, content[:5], StorageFilePerm)
@@ -342,12 +339,12 @@ func TestContentStorage_StoreHashedReplacesFileOfAnotherSize(t *testing.T) {
 		t.Fatalf("writing a partial file: %v", err)
 	}
 
-	_, err = storage.StoreHashed(hash, content)
+	_, err = storage.Store(key, content)
 	if err != nil {
-		t.Fatalf("StoreHashed() error = %v", err)
+		t.Fatalf("Store() error = %v", err)
 	}
 
-	stored, err := storage.Load(hash)
+	stored, err := storage.Load(key)
 	if err != nil {
 		t.Fatalf("Load() error = %v", err)
 	}