refactor(stream-parsing): restructured stream utilities to use Web standard APIs and generic SSE parsing

- Refactored SSE stream parsing to use generic `readSseJson` utility instead of domain-specific handlers across multiple packages.
- Migrated from Node.js Buffer API to Web standard APIs (Uint8Array, TextDecoder, DataView) for cross-platform compatibility.
- Simplified stream transformation pipeline by consolidating multiple stream operations into unified `createTextLineSplitter` utility.
- Refactored `ptree.ts` to remove complex stream pumping infrastructure and simplify stderr handling with direct async iteration.
- Rewrote stream utilities to operate at binary level with byte-level parsing for improved efficiency and reduced string allocations.
- Updated TypeScript configuration to include DOM.AsyncIterable type definitions for async iterable DOM API support.

packages/coding-agent/src/ssh/ssh-executor.ts

@@ -79,6 +79,7 @@ export async function executeSSH(
 	using child = ptree.spawn(["ssh", ...(await buildRemoteCommand(host, resolvedCommand))], {
 		signal: options?.signal,
 		timeout: options?.timeout,
+		exposeStderr: true,
 	});
 
 	const sink = new OutputSink({
@@ -87,9 +88,11 @@ export async function executeSSH(
 		artifactId: options?.artifactId,
 	});
 
-	await Promise.allSettled([child.stdout.pipeTo(sink.createInput()), child.stderr.pipeTo(sink.createInput())]).catch(
-		() => {},
-	);
+	const streams = [child.stdout.pipeTo(sink.createInput())];
+	if (child.stderr) {
+		streams.push(child.stderr.pipeTo(sink.createInput()));
+	}
+	await Promise.allSettled(streams).catch(() => {});
 
 	try {
 		return {