fix(shared): handle Windows rename-over-existing in write-file-atomically (#3222)

On Windows, renameSync fails with EPERM/EACCES when the target file
already exists. Fall back to unlink + rename on Windows permission
errors while preserving atomic semantics on other platforms.

🤖 Generated with OhMyOpenCode assistance
https://github.com/code-yeongyu/oh-my-opencode

src/shared/write-file-atomically.ts

@@ -1,13 +1,28 @@
-import { closeSync, fsyncSync, openSync, renameSync, writeFileSync } from "node:fs"
+import { closeSync, fsyncSync, openSync, renameSync, unlinkSync, writeFileSync } from "node:fs"
 
 export function writeFileAtomically(filePath: string, content: string): void {
-  const tempPath = `${filePath}.tmp`
-  writeFileSync(tempPath, content, "utf-8")
+	const tempPath = `${filePath}.tmp`
+	writeFileSync(tempPath, content, "utf-8")
   const tempFileDescriptor = openSync(tempPath, "r")
   try {
     fsyncSync(tempFileDescriptor)
   } finally {
     closeSync(tempFileDescriptor)
   }
-  renameSync(tempPath, filePath)
+
+  try {
+    renameSync(tempPath, filePath)
+  } catch (error) {
+    const isWindows = process.platform === "win32"
+    const isPermissionError =
+      error instanceof Error &&
+      (error.message.includes("EPERM") || error.message.includes("EACCES"))
+
+    if (isWindows && isPermissionError) {
+      unlinkSync(filePath)
+      renameSync(tempPath, filePath)
+    } else {
+      throw error
+    }
+  }
 }