fix(gateway): honor tty flag for interactive exec

[emonq]

Summary

Honor the requested TTY mode throughout the interactive SSH relay. When TTY is disabled, the gateway skips PTY allocation and ignores resize events, preserving pipe-based execution semantics.

Related Issue

Fixes #2228

Changes

• Pass ExecSandboxRequest.tty through the interactive exec relay.
• Request an SSH PTY only when tty=true.
• Forward terminal resize events only for PTY-backed sessions.
• Add E2E regression coverage verifying all three standard file descriptors are non-TTY with tty=false and TTY-backed with tty=true.

Testing

• mise run pre-commit all passed.

• cargo test -p openshell-server interactive_exec --lib — 10 passed.

• e2e/python/test_sandbox_api.py::test_sandbox_interactive_exec_honors_tty against a Docker-backed gateway — 1 passed.

• cargo fmt --all -- --check — passed.

• Ruff format and lint checks — passed.

• mise run pre-commit passes

• Unit tests added/updated — existing focused unit tests passed; behavior is covered by E2E.

• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[emonq]

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[emonq]

recheck

[johntmyers]

gator-agent

PR Review Status

Validation: This is a focused gateway bug fix for confirmed issue #2228. It honors the existing ExecSandboxRequest.tty contract without changing sandbox policy, authentication, or privilege boundaries.
Head SHA: bdfe2bc075a393cc3d56520db0836c73d97d803b

Review findings:

• The production change correctly passes the TTY flag through the interactive relay, allocates a PTY only when requested, and ignores resize events for pipe-backed sessions.
• Please strengthen test_sandbox_interactive_exec_honors_tty before pipeline handoff. The test currently combines stdout and stderr and never sends a streamed stdin frame, so it would pass even if stderr were returned as stdout or interactive stdin forwarding regressed. Send a stdin sentinel after the start frame, emit distinct stdout/stderr sentinels, collect the streams separately, and assert the stdin round-trip plus stream separation for tty=false while retaining the NNN/TTT checks.

Docs: No Fern update is needed; this restores behavior already documented by the protobuf contract and the existing --tty/--no-tty documentation.

Next state: gator:in-review