diff --git a/build/npm/postinstall.ts b/build/npm/postinstall.ts
index 5ab9d682857..db659fa78a4 100644
--- a/build/npm/postinstall.ts
+++ b/build/npm/postinstall.ts
@@ -182,6 +182,32 @@ function clearInheritedNpmrcConfig(dir: string, env: NodeJS.ProcessEnv): void {
 	}
 }
 
+function ensureAgentHarnessLink(sourceRelativePath: string, linkPath: string): 'existing' | 'junction' | 'symlink' | 'hard link' {
+	if (fs.existsSync(linkPath)) {
+		return 'existing';
+	}
+
+	const sourcePath = path.resolve(path.dirname(linkPath), sourceRelativePath);
+	const isDirectory = fs.statSync(sourcePath).isDirectory();
+
+	try {
+		if (process.platform === 'win32' && isDirectory) {
+			fs.symlinkSync(sourcePath, linkPath, 'junction');
+			return 'junction';
+		}
+
+		fs.symlinkSync(sourceRelativePath, linkPath, isDirectory ? 'dir' : 'file');
+		return 'symlink';
+	} catch (error) {
+		if (process.platform === 'win32' && !isDirectory && (error as NodeJS.ErrnoException).code === 'EPERM') {
+			fs.linkSync(sourcePath, linkPath);
+			return 'hard link';
+		}
+
+		throw error;
+	}
+}
+
 async function runWithConcurrency(tasks: (() => Promise<void>)[], concurrency: number): Promise<void> {
 	const errors: Error[] = [];
 	let index = 0;
@@ -294,15 +320,15 @@ async function main() {
 	fs.mkdirSync(claudeDir, { recursive: true });
 
 	const claudeMdLink = path.join(claudeDir, 'CLAUDE.md');
-	if (!fs.existsSync(claudeMdLink)) {
-		fs.symlinkSync(path.join('..', '.github', 'copilot-instructions.md'), claudeMdLink);
-		log('.', 'Symlinked .claude/CLAUDE.md -> .github/copilot-instructions.md');
+	const claudeMdLinkType = ensureAgentHarnessLink(path.join('..', '.github', 'copilot-instructions.md'), claudeMdLink);
+	if (claudeMdLinkType !== 'existing') {
+		log('.', `Created ${claudeMdLinkType} .claude/CLAUDE.md -> .github/copilot-instructions.md`);
 	}
 
 	const claudeSkillsLink = path.join(claudeDir, 'skills');
-	if (!fs.existsSync(claudeSkillsLink)) {
-		fs.symlinkSync(path.join('..', '.agents', 'skills'), claudeSkillsLink);
-		log('.', 'Symlinked .claude/skills -> .agents/skills');
+	const claudeSkillsLinkType = ensureAgentHarnessLink(path.join('..', '.agents', 'skills'), claudeSkillsLink);
+	if (claudeSkillsLinkType !== 'existing') {
+		log('.', `Created ${claudeSkillsLinkType} .claude/skills -> .agents/skills`);
 	}
 
 	// Temporary: patch @github/copilot-sdk session.js to fix ESM import