Two agents

An app's JavaScript runtime should have one Parallax debugger at a time: two debugger sessions on one Hermes runtime have crashed an app. So Parallax holds one lock per app.

With the Parallax window openCopy Anchor Link

All agents share the window's single core. Nothing to do: every agent can use the app tools, and the window sees every call.

Without the windowCopy Anchor Link

Each agent's MCP server starts a core of its own. The first one that attaches to the app takes the per-app debugger lock (a private file in the debuggers folder next to the run directory; a lock left by a dead process is taken over). A second core does not attach. Its app tools answer no_app_target:

Another Parallax core (pid N, started HH:MM) is already attached to this app as its debugger

The next app call attaches once the other core has exited. So without the window, use the app tools from one agent at a time. The device tools (screen and input) are not affected. doctor and status warn about another live core on the same app.

A debugger of someone else, such as React Native DevTools, holds no lock and is not reported.

See also Troubleshooting.