Terminal: restore original termios on panic and terminating signals

[exlier]

Problem: when the shell panics or is killed while the terminal is in raw/cbreak mode, the terminal can be left unusable (no echo / broken input).
Fix: save the original termios at startup and restore it from a panic hook and for terminating signals (SIGTERM, SIGQUIT, SIGHUP).
Files changed: src/tty.rs (new), src/main.rs, src/job_control.rs.
This prevents users from needing to run reset or reopen the terminal after a crash. Closes #94

Summary by CodeRabbit

• Bug Fixes
  • Terminal settings are now restored when the application exits due to termination signals, including SIGTERM, SIGQUIT, and SIGHUP.
  • Terminal settings are also restored after a panic, helping prevent the terminal from being left in an unusable state.
  • The application warns if it cannot save the original terminal configuration at startup.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 48cb9566-1736-42e7-a46d-84f81d2194b2

📥 Commits

Reviewing files that changed from the base of the PR and between da28f17 and 6f0e4e5.

📒 Files selected for processing (3)

• src/job_control.rs
• src/main.rs
• src/tty.rs

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📝 Walkthrough

Walkthrough

The shell now saves stdin terminal attributes at startup and restores them during panic handling and selected termination signals. Restoration uses synchronized global state and best-effort system calls.

Changes

Terminal cleanup

Layer / File(s)	Summary
Termios storage and restoration src/tty.rs	Stores original stdin termios attributes once and restores them with tcsetattr.
Startup and panic cleanup src/main.rs	Saves terminal attributes at startup, warns on save failure, and restores them before default panic handling.
Termination signal cleanup src/job_control.rs	Handles SIGTERM, SIGQUIT, and SIGHUP, restores terminal attributes, and exits with status 128 + signal.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Shell
  participant tty
  participant Terminal
  participant SignalOrPanic
  Shell->>tty: save_original_termios
  tty->>Terminal: tcgetattr
  Terminal-->>tty: original attributes
  SignalOrPanic->>tty: restore_original_termios
  tty->>Terminal: tcsetattr

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Possibly related PRs

• TruFoundation/TruShell#89: Extends related signal handling and terminal-control logic.
• TruFoundation/TruShell#91: Adds related terminal integration in src/main.rs.

Suggested reviewers: elianthorne

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes restoring terminal settings during panics and terminating signals.
Linked Issues check	✅ Passed	The changes save terminal settings and restore them during panics and SIGTERM, SIGQUIT, or SIGHUP termination, meeting issue #94.
Out of Scope Changes check	✅ Passed	The changes are limited to terminal-state preservation, panic cleanup, and terminating-signal handling required by issue #94.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch fix/tty-restore-on-panic

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❌ Failed to create PR with unit tests: AGENT_CHAT: Failed to open pull request