RuntimeWire reports discovering a functional but undocumented command-line interface in Cursor 3.16.17 called Desktop Bridge that lets shell scripts enumerate and send messages into AI agent conversations already running in the Cursor desktop app. The researchers activated the feature via Cursor's test-flag mechanism and verified it works: `cursor desktop ls` lists open threads as JSON (including thread ID, title, status, window), and `cursor desktop send <thread> [text...]` injects new instructions that trigger agent turns. The feature is gated behind a server-side feature flag and a disabled-by-default user setting both called `desktop_bridge`. Importantly, the source notes this *isn't* Cursor's public SDK Bridge—it's a separate control surface for desktop conversations specifically. Authentication uses a random bearer token stored in `.cursor/desktop-bridge` with owner-only file permissions, protecting against unauthenticated local calls but not against same-user processes. The researchers did not test the `--force` interrupt option or cloud-sourced threads. The command cannot create agents, retrieve transcripts, or echo responses back to the terminal. Cursor's public CLI documentation contains no mention of this feature as of August 18, 2026. One open question: what's Cursor's threat model for same-user process isolation, and will Desktop Bridge remain gated before broader release?