fix: fix race in reconnecting-pty/screen #19248
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…onnection to avoid race on first attach When the first attach is opened only for connection reporting and closed immediately, the screen readiness wait (screen -X version) inherited the connection context and was canceled, but Attach treated context.Canceled as success. That left no master session, and subsequent attaches failed with ‘Cannot find master process to attach to!’. Use the attach context directly for readiness (do not cancel it on output reader exit), so the session must reach the ready state or fail. Co-authored-by: sreya <4856196+sreya@users.noreply.github.com>
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Context: Screen backend used a readiness probe (screen -X version) tied to a cancel coming from the output reader, so an initial short-lived attach (e.g., for connection reporting) could cancel the wait and leave no master session. Subsequent attaches then failed with "Cannot find master process to attach to!" and tests would fail attempting to find the prompt.
Change: decouple the readiness probe from the output reader cancellation; use the attach context directly so the session must reach ready or fail. This prevents the flake where the first quick connect/disconnect prevents actual session creation.
Tested: ran agent package tests locally; Screen subtest is skipped here without
screen, but the change is isolated to screen backend.Co-authored-by: sreya 4856196+sreya@users.noreply.github.com