Forward POSIX shutdown signals to supervised processes in JSON mode

[harsh21234i]

Summary

When reflex run --json supervises a child process, a SIGINT sent to the supervisor PID can interrupt the supervisor without stopping the child. Forward SIGINT to the running child on POSIX so process supervisors configured with stopsignal=INT can stop Reflex cleanly.

Closes #7509.

Testing

• uv run pytest tests/units/reflex_base/utils/test_log.py -q — 80 passed, 2 skipped on Windows.
• Linux PID-targeted SIGINT regression test — 1 passed.
• Applicable pre-commit hooks — passed.

[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Reply with feedback, questions, or to request a fix.

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[greptile-apps]

Confidence Score: 5/5

[High impact] The PR appears safe to merge; the previous terminal quit issue is fixed.

Summary

On POSIX, reflex run --json forwards shutdown signals to the child's process group and waits for the child.

• JSON mode forwards POSIX shutdown signals to the supervised app.

_{Reviews (6) · Last reviewed commit: "fix: forward SIGQUIT to supervised proce..." · Reviewed by Greptile}

[codspeed]

Merging this PR will not alter performance

⚠️ 10 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• test_cli_startup[version]
• test_cli_startup[help]
• test_cli_startup[deploy_help]
• test_modify_state[disk]
• test_import_cli
• test_set_state[disk]
• test_cli_startup[cloud_help]
• test_python_process_startup
• test_emit_update
• test_cli_startup[run_help]

✅ 148 untouched benchmarks

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_{Comparing harsh21234i:fix/7509-json-run-sigint (b78bd1a) with main (7ccaa4e)}

[cubic-dev-ai]

All reported issues were addressed across 4 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

View guided diff | Re-trigger cubic</sub>