test(python): synchronize interactive exec TTY readiness

[matthewgrossman]

Summary

Prevent a false failure in test_sandbox_interactive_exec_honors_tty when PTY stdin echo lands between the shell's separate TTY flag writes. Wait for a complete output readiness marker before submitting stdin, so a successful terminal execution cannot turn TTT into TTstreamed-stdin-sentinel\r\nT.

CI Evidence

Observed in PR #4066's Branch E2E Checks on October 1, 2026, at SHA 6c4bb7614af2d86783e8a887b8915ef1520e94df:

• Failed Docker Python E2E job, attempt 2: test_sandbox_interactive_exec_honors_tty failed because stdout contained TTstreamed-stdin-sentinel\r\nT instead of contiguous TTT. All three TTY flags, consumed stdin, both output sentinels, and exit code zero were present. Suite result: 1 failed, 59 passed, 81 skipped.
• Passed Docker Python E2E job, attempt 1: the same test passed at the same SHA. Suite result: 60 passed, 81 skipped.

This was a pre-existing test race exposed on the PR branch; PR #4066 does not modify this test or the interactive runtime.

Changes

• Accumulate output across gRPC events, recognize the complete readiness marker with CRLF normalization, and gate stdin with a bounded event wait. Unblock the request iterator on early exit or RPC failure.
• Require exact TTY flag lines, verify consumed stdin and both output sentinels in TTY mode, and preserve non-TTY stdout/stderr separation checks.

Testing

• Ruff lint, focused formatting, test collection, and git diff --check pass.
• Configured mise run pre-commit hook passes, including repository lint, formatting, license, protobuf, Helm, and SDK checks.
• E2E assertions and input synchronization updated.
• Applied test passes 160 trials through a local service using real PTYs/pipes and Python bidirectional gRPC: 100 ordinary, 30 forced-interleaving, and 30 with one-byte output events. The original test fails 10/10 trials under the same forced ordering with the exact CI transcript.
• The applied test rejects lost TTY support, merged non-TTY streams, lost consumed stdin in either mode, missing TTY output sentinels, early exit, RPC errors, and missing readiness. The actual readiness timeout was exercised; no input-consumption threads remained blocked.
• Full Docker-backed OpenShell Python E2E lane. The local Docker daemon is unavailable; the local harness does not run the Rust gateway, SSH relay, or Linux isolation backend. Draft pending CI validation.

The change is limited to this E2E test; the adjacent request-EOF/output-draining test remains intact.

Checklist

• Follows Conventional Commits.
• Commit is signed off for DCO.
• Architecture docs: not applicable to this test-only change.

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.