fix: preserve external output path spelling (#7) (thanks @jesse-merhi)

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixes
 
+- Add `writeExternalFileWithinRoot()` for libraries that require an output path while preserving caller-provided destination names. (#7; thanks @jesse-merhi)
 - Reject `fileStore()` and `fileStoreSync()` writes through symlinked parent directories so store commits cannot escape the configured root.
 - Harden Root fallback mutators, archive merges, private store reads/writes, durable queue ids, JSON fallback writes, sibling temp writes, temp filename sanitization, and trash moves against symlink-swap and path traversal edge cases.
 - Centralize safe path segment validation, directory identity guards, and guarded mutation wrappers so future filesystem helpers reuse the same race-resistant checks.

src/output.ts

@@ -65,8 +65,8 @@ export async function writeExternalFileWithinRoot<T = void>(
   options: ExternalFileWriteOptions<T>,
 ): Promise<ExternalFileWriteResult<T>> {
   const targetRoot = await root(options.rootDir);
-  const requestedTargetPath = options.path.trim();
-  if (!requestedTargetPath) {
+  const requestedTargetPath = options.path;
+  if (requestedTargetPath.length === 0) {
     throw new FsSafeError("invalid-path", "target path is required");
   }
   const targetPath = toRootPathInput({

test/output.test.ts

@@ -42,6 +42,26 @@ describe("writeExternalFileWithinRoot", () => {
     await expect(fs.stat(tempPath)).rejects.toMatchObject({ code: "ENOENT" });
   });
 
+  it("preserves caller-provided destination filename spacing", async () => {
+    const rootDir = await tempRoot("fs-safe-output-spaces-");
+    const fileName = " report .txt ";
+
+    const result = await writeExternalFileWithinRoot({
+      rootDir,
+      path: fileName,
+      write: async (candidate) => {
+        await fs.writeFile(candidate, "spaced", "utf8");
+      },
+    });
+
+    const finalPath = path.join(rootDir, fileName);
+    expect(result.path).toBe(path.join(await fs.realpath(rootDir), fileName));
+    await expect(fs.readFile(finalPath, "utf8")).resolves.toBe("spaced");
+    await expect(fs.stat(path.join(rootDir, fileName.trim()))).rejects.toMatchObject({
+      code: "ENOENT",
+    });
+  });
+
   it("rejects empty target paths before invoking the external writer", async () => {
     const rootDir = await tempRoot("fs-safe-output-default-");
     let called = false;