feat(files): add save-as-new vs overwrite choice for library file edits (#564)

Editing a file from the library used to silently supersede it: the worker auto-saved every result as a new version and the leaf-only listing hid the original, which read as a destructive overwrite. Tool pages now show a per-edit choice for library-sourced files. The default saves the result as an independent new file and keeps the original; picking overwrite keeps the old superseding-version behavior.

The client sends a saveMode multipart field next to fileId, validated with a 400 on unknown values, and autoSaveToLibrary branches on it. Every hand-written route that honors fileId parses the field the same way as the factory. The review panel shows where an auto-saved result went instead of offering a second, duplicate save. Tools whose route or submitter ignores fileId keep the selector hidden via a shared unsupported-tools set, and the choice resets to the non-destructive default whenever a new file is staged.

Closes #495

tests/unit/web/stores/file-store-save-mode.test.ts

@@ -0,0 +1,83 @@
+// @vitest-environment jsdom
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const revokeObjectURL = vi.fn();
+const createObjectURL = vi.fn((_obj: Blob | MediaSource) => "blob:fake-url");
+
+vi.stubGlobal("URL", {
+  ...globalThis.URL,
+  createObjectURL,
+  revokeObjectURL,
+});
+
+const imagePreviewMock = vi.hoisted(() => ({
+  needsServerPreview: vi.fn(() => false),
+  fetchDecodedPreview: vi.fn(() => Promise.resolve(null)),
+}));
+
+vi.mock("@/lib/image-preview", () => imagePreviewMock);
+
+vi.mock("@/lib/analytics", () => ({
+  track: vi.fn(),
+}));
+
+import { useFileStore } from "@/stores/file-store";
+
+function makeFile(name: string, size = 1024, type = "image/png"): File {
+  const buf = new ArrayBuffer(size);
+  return new File([buf], name, { type });
+}
+
+describe("useFileStore library save mode (issue #495)", () => {
+  beforeEach(() => {
+    useFileStore.getState().reset();
+    vi.clearAllMocks();
+  });
+
+  it("defaults librarySaveMode to non-destructive 'new'", () => {
+    expect(useFileStore.getState().librarySaveMode).toBe("new");
+  });
+
+  it("setLibrarySaveMode switches the mode", () => {
+    useFileStore.getState().setLibrarySaveMode("overwrite");
+    expect(useFileStore.getState().librarySaveMode).toBe("overwrite");
+  });
+
+  it("reset restores the 'new' default and clears the last saved file id", () => {
+    useFileStore.getState().setLibrarySaveMode("overwrite");
+    useFileStore.getState().setLastSavedLibraryFileId("lib-1");
+
+    useFileStore.getState().reset();
+
+    expect(useFileStore.getState().librarySaveMode).toBe("new");
+    expect(useFileStore.getState().lastSavedLibraryFileId).toBeNull();
+  });
+
+  it("undoProcessing keeps the chosen mode but clears the last saved file id", () => {
+    useFileStore.getState().setFiles([makeFile("a.png")]);
+    useFileStore.getState().setLibrarySaveMode("overwrite");
+    useFileStore.getState().setLastSavedLibraryFileId("lib-2");
+
+    useFileStore.getState().undoProcessing();
+
+    expect(useFileStore.getState().librarySaveMode).toBe("overwrite");
+    expect(useFileStore.getState().lastSavedLibraryFileId).toBeNull();
+  });
+
+  it("staging a new file set restores the non-destructive default", () => {
+    useFileStore.getState().setFiles([makeFile("a.png")]);
+    useFileStore.getState().setLibrarySaveMode("overwrite");
+
+    // A later library import stages a different file; the overwrite choice
+    // made for the previous file must not carry over (#495 review finding).
+    useFileStore.getState().setFiles([makeFile("b.png")]);
+
+    expect(useFileStore.getState().librarySaveMode).toBe("new");
+  });
+
+  it("tracks the last saved library file id", () => {
+    expect(useFileStore.getState().lastSavedLibraryFileId).toBeNull();
+    useFileStore.getState().setLastSavedLibraryFileId("lib-3");
+    expect(useFileStore.getState().lastSavedLibraryFileId).toBe("lib-3");
+  });
+});