fix: guard case-only rename recovery

src/apps/webapp/adapters/FSAPIStorageAdapter.unit.spec.ts

@@ -8,7 +8,10 @@ class MemoryFileHandle {
     readonly kind = "file";
     private data = new Uint8Array();
 
-    constructor(readonly name: string) {}
+    constructor(
+        readonly name: string,
+        private readonly shouldFailWrite: () => boolean = () => false
+    ) {}
 
     async getFile(): Promise<File> {
         return new File([this.data], this.name, { lastModified: 1 });
@@ -18,6 +21,7 @@ class MemoryFileHandle {
         const handle = this;
         return {
             async write(data: FileSystemWriteChunkType) {
+                if (handle.shouldFailWrite()) throw new Error(`write failed: ${handle.name}`);
                 if (typeof data === "string") {
                     handle.data = new TextEncoder().encode(data);
                 } else if (data instanceof ArrayBuffer) {
@@ -36,6 +40,7 @@ class MemoryFileHandle {
 class MemoryDirectoryHandle {
     readonly kind = "directory";
     private readonly children = new Map<string, MemoryDirectoryHandle | MemoryFileHandle>();
+    private readonly failedWriteNames = new Set<string>();
 
     constructor(
         readonly name: string,
@@ -65,7 +70,7 @@ class MemoryDirectoryHandle {
         const existing = this.children.get(resolvedName);
         if (existing instanceof MemoryFileHandle) return existing as unknown as FileSystemFileHandle;
         if (existing !== undefined || !options?.create) throw new DOMException("File not found", "NotFoundError");
-        const file = new MemoryFileHandle(name);
+        const file = new MemoryFileHandle(name, () => this.failedWriteNames.has(name));
         this.children.set(name, file);
         return file as unknown as FileSystemFileHandle;
     }
@@ -89,6 +94,10 @@ class MemoryDirectoryHandle {
     names(): string[] {
         return [...this.children.keys()];
     }
+
+    failWritesTo(name: string): void {
+        this.failedWriteNames.add(name);
+    }
 }
 
 describe("FSAPIStorageAdapter", () => {
@@ -114,6 +123,21 @@ describe("FSAPIVaultAdapter.rename", () => {
         expect(await (await renamedHandle.getFile()).text()).toBe("content");
         expect(file.path).toBe("calculus.md");
     });
+
+    it("removes a partially created target before restoring the source", async () => {
+        const memoryRoot = new MemoryDirectoryHandle("root");
+        const root = memoryRoot as unknown as FileSystemDirectoryHandle;
+        const adapter = new FSAPIVaultAdapter(root);
+        const file = await adapter.create("Calculus.md", "content");
+        memoryRoot.failWritesTo("calculus.md");
+
+        await expect(adapter.rename(file, "calculus.md")).rejects.toThrow("write failed");
+
+        expect(memoryRoot.names()).toEqual(["Calculus.md"]);
+        const restoredHandle = await root.getFileHandle("Calculus.md");
+        expect(await (await restoredHandle.getFile()).text()).toBe("content");
+        expect(file.path).toBe("Calculus.md");
+    });
 });
 
 describe("FSAPIFileSystemAdapter path case", () => {

src/apps/webapp/adapters/FSAPIVaultAdapter.ts

@@ -97,6 +97,23 @@ export class FSAPIVaultAdapter implements IVaultAdapter<FSAPIFile> {
         };
     }
 
+    private async deletePathIfExists(path: string): Promise<void> {
+        const parts = path.split("/").filter((part) => part !== "");
+        const name = parts.pop();
+        if (!name) return;
+
+        try {
+            let currentHandle = this.rootHandle;
+            for (const part of parts) {
+                currentHandle = await currentHandle.getDirectoryHandle(part);
+            }
+            await currentHandle.removeEntry(name);
+        } catch (error) {
+            if ((error as { name?: unknown })?.name === "NotFoundError") return;
+            throw error;
+        }
+    }
+
     async rename(file: FSAPIFile, newPath: string): Promise<void> {
         const source = await file.handle.getFile();
         const data = await source.arrayBuffer();
@@ -120,6 +137,13 @@ export class FSAPIVaultAdapter implements IVaultAdapter<FSAPIFile> {
             file.stat = renamedFile.stat;
             file.handle = renamedFile.handle;
         } catch (error) {
+            try {
+                await this.deletePathIfExists(newPath);
+            } catch (cleanupError) {
+                throw new Error(
+                    `Could not rename ${oldPath} to ${newPath}, or remove the incomplete target. A temporary copy remains at ${temporaryPath}. Rename error: ${String(error)}. Cleanup error: ${String(cleanupError)}`
+                );
+            }
             try {
                 const restoredFile = await this.createBinary(oldPath, data);
                 file.path = restoredFile.path;