Exit a stopped render when no terminal is attached

[gorandodig]

A render started without a terminal no longer spins at 100% CPU, and a stopped one exits with status 1 instead of waiting for an Enter nobody can press.

What happens now

When stdin, stdout or stderr is not a terminal, codeplain renders as --headless does, and says so on the first line:

[00:00:00] INFO codeplain: No terminal attached, so rendering without the TUI, as with --headless.

Progress streams to stdout as it happens, and a render that stops exits with status 1, the same status --headless gives. A render that completes exits 0. Started from a terminal, nothing changes: the TUI runs, and after a stop it waits for Enter at 0% CPU.

Why it happened

The TUI is Textual, and Textual reads keys from stdin in a thread. A script or an agent starts codeplain with stdin at end-of-file (/dev/null, which is also what a non-interactive shell gives a background & job). End-of-file is always "ready to read", so the thread's select() returns at once, read() returns nothing, and it loops again: 2.76 million empty reads in 4 seconds. That pins a core for the whole render, not only after the stop. Once the render stopped, the TUI waited for Enter, which could never arrive, so the process stayed alive until it was killed.

Why fall back to headless, rather than make the TUI exit on stop

• It fixes the spin for the whole render. Exiting on stop would leave the input thread spinning from the first second to the stop.
• render.log gets readable progress lines instead of screen-drawing escape codes (23 KB of them in 12 seconds here).
• The resume-choice prompt is a TUI too, and would wait for a key the same way. Headless already skips it.
• The exit status is --headless's by construction, not a second implementation of it.

It checks all three streams because the TUI needs all three: keys come from stdin, Textual draws on stderr, and the exit summary goes to stdout. Checking stdout also covers codeplain module.plain > render.log 2>&1 & from an interactive shell. There stdin is still the terminal, but a background job that changes the terminal settings is stopped by the shell (Stopped (tty output)), so before this the render never got going.

Verification

A local harness, no live render: it runs the real plain2code.main() on the hello-world example with the API connection check, the API report and telemetry stubbed. Its module renderer "renders" for 2 seconds, then stops the way a functionality still failing its unit tests does: it marks the render unsuccessful and publishes RenderFailed. Argument parsing, logging, the headless/TUI decision, the TUI and the exit status are the real code.

No terminal: python harness_main_stop.py hello_world_python.plain </dev/null >render.log 2>&1 &, with ps -o %cpu=,time= sampled each second.

	before (main)	after
CPU while rendering (0 to 2 s)	94 to 100%	8% at start-up, then 0.1%
CPU after the stop	98 to 100%, still running at 12 s, killed	the process had exited
exit status	none, killed	1
explicit --headless	1	1

As a background job of an interactive bash on a pseudo-terminal (... > render.log 2>&1 &): before, jobs -l shows Stopped (tty output) and the render never reaches its stop; after, it shows Exit 1.

With a terminal (the harness under a pseudo-terminal, Enter sent 8 s in), before and after are same: 0.0 to 0.4% CPU while waiting for Enter, and Enter exits.

New tests in tests/test_terminal_attachment.py:

• attached_to_terminal() is false when any of stdin, stdout or stderr is not a terminal, or is missing.
• Through the real main() and render(), with no terminal: the TUI never starts, the resume-choice TUI is never opened, a stopped render exits 1, a completed one exits 0, and the log says why. With a terminal the TUI still runs and nothing is logged about it.
• Under a real pseudo-terminal, the stopped TUI uses under 0.5 CPU-seconds over 2 seconds of waiting, and Enter exits it. The same measurement with stdin at end-of-file reads 2.0 CPU-seconds, so it catches a spin. Skipped on Windows.

The existing main() tests in tests/test_render_finished_report.py describe a TUI render, so they now pin a terminal. Under pytest there is none, and they would otherwise switch to headless.

Not changed

A stopped render in the TUI still exits 0 after Enter. Only headless mode turns a stop into a non-zero status, and that is unchanged here.

Summary by CodeRabbit

• New Features
  • The app now automatically uses headless mode when stdin, stdout, or stderr is not connected to a terminal. Non-terminal runs use headless logging and exit handling instead of the interactive progress display and resume prompts.
  • Updated the --headless help text and documentation to explain when automatic detection applies.

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• tests/test_terminal_attachment.py

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📝 Walkthrough

The CLI checks whether stdin, stdout, and stderr are attached to terminals. If any stream is not attached and --headless was not requested, it enables headless rendering, suppresses Rich console output, and prints a notice. Documentation and tests cover the selection and render behavior.

Changes: Terminal-aware rendering

Layer / File(s)	Summary
Terminal detection and headless selection plain2code.py, plain2code_arguments.py, docs/plain2code_cli.md	The CLI checks all three standard streams for terminal attachment. When any stream is not attached, it enables headless mode unless requested otherwise. The help text and CLI documentation describe this behavior.
Render behavior and terminal tests tests/test_terminal_attachment.py, tests/test_render_finished_report.py	Tests cover stream detection, terminal and non-terminal render outcomes, stopped-render behavior in a POSIX pseudo-terminal, and a fixture that forces terminal attachment.

Priority: ➖ Normal

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

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant main
  participant attached_to_terminal
  participant StandardStreams
  participant Render
  participant ProgressTUI
  main->>attached_to_terminal: Check terminal attachment
  attached_to_terminal->>StandardStreams: Check isatty() for each standard stream
  StandardStreams-->>attached_to_terminal: Return attachment status
  attached_to_terminal-->>main: Return combined status
  alt A stream is not attached and headless was not requested
    main->>Render: Enable headless mode and print notice
  else All streams are attached
    main->>ProgressTUI: Run progress interface
  end

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Merge Risk: ⚪ Minimal · up to a4c93

Non-terminal runs now use headless rendering while terminal sessions retain the TUI. The supplied code and test evidence show no remaining actionable merge risk.

Security architecture risk: 🔵 Low · up to a4c93

The change reuses existing authenticated rendering rather than introducing a new privileged path. No concrete security regression was identified, but non-terminal runs now skip interactive resume choices automatically. The downstream fallback’s complete mutation behavior and external handling of progress output were not fully established.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The traced exposure remains the invoking process’s configured API identity and selected module chain. Stream redirection can now select unattended execution, but the inspected routing does not supply different credentials, module owners, or rendering arguments.

Trust Boundaries and Controls

• observed — Terminal attachment is a presentation and orchestration selector, not the API identity control. Nevertheless, automatic selection newly skips resume interaction for redirected runs; clearing a destructive choice should not be interpreted as proof that all fallback mutations are non-destructive.

Resilience and Maintainability Implications

• observed — Completion reporting distinguishes cancellation, success, and failure, requires an established user email, and suppresses reporting exceptions so they do not replace the render outcome. These controls are shared by automatic and explicit headless execution.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 34.62% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 26 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: exiting stopped renders when no terminal is attached.

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Actionable comments posted: 1

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Inline comments:
Review comments at @tests/test_terminal_attachment.py:
- Line 16: Move the Unix-only fcntl and termios imports from module scope into
test_a_stopped_render_on_a_terminal_waits_for_enter_without_spinning, preserving
the test’s existing skip behavior so other tests can be collected on Windows.

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• docs/plain2code_cli.md
• plain2code.py
• plain2code_arguments.py
• tests/test_render_finished_report.py
• tests/test_terminal_attachment.py

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[pedjaradenkovic]

Very good improvement. I'll leave the testing to you, but the code and logic looks good 👍