macOS: claude:// gets registered to the Electron helper bundle, login fails with Finder error -600
Claude Desktop 1.24012.9, macOS 26 (Darwin 25.3.0).
After the browser login flow, macOS shows a Finder dialog "Unable to open the application. -600" and the app never receives the callback.
Cause: the claude:// URL scheme handler in LaunchServices is set to com.anthropic.claudefordesktop.helper instead of com.anthropic.claudefordesktop. All four helper bundles inside Contents/Frameworks share that same identifier and none of them is launchable, so LSOpenURLsWithRole fails with procNotFound (-600).
It looks like app.setAsDefaultProtocolClient is being called from a helper process: NSWorkspace.urlForApplication(toOpen:) resolves claude:// to Claude Helper (Plugin).app. The registration is rewritten by the app itself, observed 9 seconds after launch and again within minutes while the app was already running, so fixing the handler manually does not stick.
Workaround for users: the "Sign in with code" link on the login page avoids the claude:// callback entirely.