A cached file checked as another is refused and left, not deleted for the next model

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/agent/weights/fetch.go

@@ -230,9 +230,17 @@ func (f *Fetcher) fetchChecked(ctx context.Context, source, target, want string)
 // the checksum kept beside it, or worked out once and then kept. One that
 // is not is deleted, to be fetched again. Any file is, when want is empty.
 func (f *Fetcher) cachedIs(target, want string) (bool, error) {
-	if want == "" || readChecksum(target) == want {
+	kept := readChecksum(target)
+	if want == "" || kept == want {
 		return true, nil
 	}
+	if kept != "" {
+		// Checked when it was fetched, as another file: the same address
+		// gives the same bytes again, and another model may be serving
+		// these. Refused, and left.
+		return false, fmt.Errorf("the copy of this file here has sha256 %s, as fetched, and the catalog names %s: refused",
+			kept, want)
+	}
 	sum, err := fileSHA256(target)
 	if err != nil {
 		return false, err

internal/agent/weights/fetch_test.go

@@ -339,3 +339,25 @@ func TestAFileThatIsNotWhatTheRegistryPublishedIsRefused(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+// A cached file checked when it was fetched, that another model names with
+// another checksum, is refused and left for the model it is.
+func TestACheckedFileAnotherChecksumNamesIsRefusedAndLeft(t *testing.T) {
+	body := "the weights"
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) { _, _ = w.Write([]byte(body)) }))
+	defer srv.Close()
+	sum := sha256.Sum256([]byte(body))
+	f := &Fetcher{CacheDir: t.TempDir()}
+	src := srv.URL + "/m.gguf"
+	path, err := f.EnsureChecked(t.Context(), src, false, hex.EncodeToString(sum[:]))
+	if err != nil {
+		t.Fatal(err)
+	}
+	wrong := strings.Repeat("0", 64)
+	if _, err := f.EnsureChecked(t.Context(), src, false, wrong); err == nil || !strings.Contains(err.Error(), wrong) {
+		t.Fatalf("not refused: %v", err)
+	}
+	if b, err := os.ReadFile(path); err != nil || string(b) != body {
+		t.Errorf("the checked file was not left: %v", err)
+	}
+}