fix: add 30s timeout to WebRTC connection_ready.wait() to prevent indefinite hang

[hculap]

Problem

Blueprint.build() and direct UnitreeWebRTCConnection(ip) hang indefinitely when the WebRTC SDP exchange fails. The root cause is connection_ready.wait() in connect() has no timeout — if the connection never establishes, the event is never set and the thread blocks forever with no error.

Common trigger: Go2 only allows one WebRTC client at a time. If the Unitree mobile app is open, the SDP exchange returns "sdp": "reject" and the event never fires. The process appears to hang with no indication of what went wrong.

Call chain:

blueprint().build()
  -> Worker.start_process()   # forkserver subprocess
    -> GO2Connection.__init__()
      -> UnitreeWebRTCConnection(ip)
        -> connect()
          -> self.connection_ready.wait()  # NO TIMEOUT — blocks forever

Fix

Add a 30-second timeout with thread cleanup and a descriptive TimeoutError listing common causes:

if not self.connection_ready.wait(timeout=CONNECT_TIMEOUT):
    if self.loop.is_running():
        self.loop.call_soon_threadsafe(self.loop.stop)
    if self.thread.is_alive():
        self.thread.join(timeout=2.0)
    raise TimeoutError(
        f"WebRTC connection to {self.ip} timed out after {CONNECT_TIMEOUT}s. "
        "Common causes:\n"
        "  - Another WebRTC client is connected (close the Unitree mobile app)\n"
        "  - Robot is unreachable on the network\n"
        "  - Port 9991 (encrypted SDP) is not responding\n"
        "Tip: only one WebRTC client can connect to the Go2 at a time."
    )

Testing

Tested on: Go2 Pro, stock firmware 1.1.7+, STA mode (home WiFi), DimOS v0.0.10.post2, macOS Apple Silicon.

• Normal connection: connects in ~15s as before, no behavior change
• Mobile app connected: raises TimeoutError after 30s with helpful message (previously: hung forever)
• Robot unreachable: raises TimeoutError after 30s (previously: hung forever)
• Blueprint surfaces error: build() now fails with TimeoutError instead of hanging

Related

Discovered while building an AI bridge for Go2 Pro: https://github.com/DataPilot-R-D/go2-ai-bridge

[spomichter]

Can you cherry pick this commit and PR it against dev? Thanks

[hculap]

Closing in favour of #1446 which targets the dev branch as requested.