fix(unix): detach Codex-launched gateways reliably

[btsouth]

What and why

Codex starts MCP children as process-group leaders. That made Toolport's setsid() fail, leaving the gateway in Codex's terminal session. The login-shell PATH probe could then receive SIGTTIN and stop the whole gateway before its first response.

Normal Unix startup now handles that launch shape and detaches before startup I/O or PATH discovery. Early diagnostic modes keep their existing terminal behavior.

Closes SBS-1063.

Testing

• Added a subprocess regression using process_group(0)
• cargo clippy --manifest-path src-tauri/Cargo.toml --no-default-features --all-targets
• cargo test --manifest-path src-tauri/Cargo.toml --no-default-features --lib --bins --tests
• Codex-style live launch with D-Bus variables removed answered status and fetched Linear

Notes

No Omarchy or client configuration changes are required.

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Note

Medium Risk
Touches process-group and session leadership at gateway startup via unsafe POSIX calls. Failure modes are fail-open to the previous best-effort detach, but a bad detach could still affect job-control or child spawn on Unix.

Overview
Unix gateways launched as process-group leaders (Codex’s MCP spawn) now leave the client’s terminal session instead of failing setsid with EPERM and stopping on SIGTTIN during the PATH probe.

detach_from_client_session briefly rejoins the parent group and retries setsid before session-bus restore or any child spawn. --selftest-secrets still skips detach so that diagnostic path keeps its old terminal behavior. A Unix subprocess test launches the binary with process_group(0) and asserts it becomes its own session.

^{Reviewed by Cursor Bugbot for commit 31bb5e5. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix gateway stall by robustly detaching from client terminal session on Unix

• Replaces the single inline setsid() call with a new detach_from_client_session() function in toolport-gateway.rs that handles the case where the gateway is already a process-group leader: it temporarily reattaches to the parent's group via setpgid(0, parent_group) then calls setsid() again.
• Moves the detach earlier in startup — before environment restoration and PATH probing — so downstream spawns and probes run without a controlling terminal. Detach is skipped when the binary is invoked with --selftest-secrets.
• Adds a Unix-only integration test in gateway_session_detach.rs that spawns the gateway as a process-group leader and polls until its session id equals its pid.
• Behavioral Change: all normal Unix startup now detaches from the client's terminal session before any probes or downstream spawns; non-Unix platforms are unchanged.

^{Macroscope summarized 31bb5e5.}

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• src-tauri/src/bin/toolport-gateway.rs
• src-tauri/tests/gateway_session_detach.rs

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📝 Walkthrough

Walkthrough

The gateway now uses a dedicated session-detachment helper. Normal startup detaches from the client session, while --selftest-secrets skips detachment. A Unix regression test validates process-group-leader startup and session separation.

Changes

Gateway session detachment

Layer / File(s)	Summary
Detachment helper and startup wiring src-tauri/src/bin/toolport-gateway.rs	The gateway adds platform-specific session detachment, skips it for --selftest-secrets, reuses the computed self-test flag, and removes the previous inline setsid block.
Session detachment regression test src-tauri/tests/gateway_session_detach.rs	A Unix-only test launches the gateway as a process-group leader, checks that it remains running, and polls for a separate session within two seconds.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 31bb5

This PR changes Unix gateway startup so Codex-launched gateways detach before startup I/O and adds regression coverage; no actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: bharadwajkanneveti, forever-ivy

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the Unix gateway detachment fix.
Description check	✅ Passed	The description explains the Unix detachment issue, implementation, behavior, testing, and related issue.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/sbs-1063-codex-session-detach

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