feat(cdp): BU_CDP_HTTP to attach to a browser on another host

Upstream can only drive a browser on localhost. The pi extension always goes
through the daemon (src/index.ts uses createDaemonTransport), the daemon
resolves Chrome with discoverWsUrl() (src/daemon/bridge.ts), and that probe is
hardcoded to 127.0.0.1 (src/cdp/discovery.ts). BU_CDP_WS is read only by the
in-process client (src/client.ts), which that path never touches, so it has no
effect on the extension - the only workaround is relaying the remote browser
onto localhost first.

BU_CDP_HTTP="host:port" points at the remote CDP HTTP endpoint. It is resolved
inside discoverEndpoint(), so the daemon and the client both honour it.

Deliberately an HTTP endpoint rather than a WebSocket URL: it is re-resolved on
every discovery call, so the browser UUID is re-read after the remote browser
restarts. Chrome re-mints that UUID on every launch, so a pinned WebSocket URL
goes stale as soon as the remote browser is recycled.

Also skips performSetup's local-process precondition when BU_CDP_HTTP is set:
isBrowserRunning() enumerates local processes and can never see a remote
browser. Step 4 still fails loudly if it is unreachable.

No userDataDir is returned for remote endpoints, since the profile registry
lives on the remote host - profile enumeration degrades to the pre-profile
behaviour rather than reading the wrong machine's Local State.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/setup.ts b/src/setup.ts
index 395fff4..44dfc2c 100644
--- a/src/setup.ts
+++ b/src/setup.ts
@@ -22,9 +22,15 @@ export function registerSetupCommand(pi: ExtensionAPI, client: BrowserClient): v
 export type SetupResult = { success: true; data: string } | { success: false; error: string };
 
 export async function performSetup(client: BrowserClient, ctx?: ExtensionContext): Promise<SetupResult> {
-  const chromeRunning = await isBrowserRunning();
-  if (!chromeRunning) {
-    return { success: false, error: "No browser instance running. Please open your browser and then run /browser-setup." };
+  // Step 1: Check Chrome is running
+  // LOCAL PATCH: isBrowserRunning() enumerates *local* processes, so it can
+  // never see a browser reached via BU_CDP_HTTP. Skip the precondition in that
+  // case — step 4 still fails loudly if the remote browser is unreachable.
+  if (!process.env["BU_CDP_HTTP"]?.trim()) {
+    const chromeRunning = await isBrowserRunning();
+    if (!chromeRunning) {
+      return { success: false, error: "No browser instance running. Please open your browser and then run /browser-setup." };
+    }
   }
 
   const daemonReady = await ensureDaemon();