Hom Terminal Integration

HOM Terminal Integration

When to Use

Invoke this skill when:

• Implementing or modifying GhosttyBackend in crates/hom-terminal/src/ghostty.rs
• Modifying Vt100Backend in crates/hom-terminal/src/fallback_vt100.rs
• Changing the TerminalBackend trait in crates/hom-core/src/traits.rs
• Working on PTY management in crates/hom-pty/src/manager.rs
• Modifying the async PTY reader in crates/hom-pty/src/async_reader.rs
• Debugging terminal rendering issues (wrong colors, missing characters, cursor position)
• Enabling the ghostty-backend feature flag

Architecture: TUI-inside-TUI

This is the hardest part of HOM. Each pane runs a REAL terminal emulator:

Harness Process (e.g., claude)
    ↓ writes ANSI escape sequences to stdout
PTY slave → PTY master
    ↓ raw bytes
AsyncPtyReader (tokio channel)
    ↓ Vec<u8> chunks
terminal.process(bytes)    ← TerminalBackend implementation
    ↓ updates internal screen state
terminal.screen_snapshot() → ScreenSnapshot { rows: Vec<Vec<Cell>> }
    ↓ cell-by-cell mapping
pane_render.rs → ratatui Buffer
    ↓
ratatui renders to real terminal

Every byte from the harness flows through this pipeline. A bug anywhere means garbled output.

The TerminalBackend Trait

Defined in crates/hom-core/src/traits.rs. Any terminal emulator must implement:

libghostty-rs Integration (Feature: ghostty-backend, DEFAULT)

Current status: Fully implemented in ghostty.rs. This is the default backend.

To build (default):

cargo build   # ghostty-backend is the default feature

Requires Zig ≥0.15.x at build time. Install Zig: brew install zig or download from ziglang.org.

Critical risk: libghostty-rs is v0.1.1, pre-1.0. Pin commits. The API WILL change.

vt100 Backend (Opt-in fallback: vt100-backend)

The opt-in fallback in fallback_vt100.rs. Uses the vt100 crate (v0.16).

To build with vt100 fallback (no Zig required):

cargo build --no-default-features --features vt100-backend

Known limitations:

• No Kitty graphics protocol
• No sixel support
• title() always returns None (vt100 0.16 doesn't expose it)
• Resize uses screen_mut().set_size() (not parser.set_size())
• No dim attribute detection

These limitations are acceptable for the current implementation. Most harness TUIs use basic text, colors, and cursor positioning.

Color Mapping

crates/hom-terminal/src/color_map.rs maps TermColor → ratatui::style::Color.

When adding a new backend, you must map its color representation to TermColor. The 16 named colors (Black through BrightWhite) plus Indexed(0-255) and Rgb(r,g,b) must all be handled.

PTY Management

crates/hom-pty/src/manager.rs uses portable-pty to:

• Open a PTY pair (master + slave)
• Spawn the harness command on the slave
• Read from master (→ terminal emulator)
• Write to master (← user input / orchestrator commands)
• Resize the PTY when the pane resizes

Critical timing issue: After spawning, the harness needs time to initialize before accepting input. Don't send prompts immediately — wait for detect_completion() == WaitingForInput.

Testing Terminal Emulation

#[test]
fn test_process_simple_text() {
    let mut term = Vt100Backend::new(80, 24, 0).unwrap();
    term.process(b"Hello, World!");
    let snap = term.screen_snapshot();
    let first_row: String = snap.rows[0].iter().map(|c| c.character).collect();
    assert!(first_row.starts_with("Hello, World!"));
}

#[test]
fn test_process_color_escape() {
    let mut term = Vt100Backend::new(80, 24, 0).unwrap();
    term.process(b"\x1b[31mRed text\x1b[0m");
    let snap = term.screen_snapshot();
    assert!(matches!(snap.rows[0][0].fg, TermColor::Red));
}

#[test]
fn test_cursor_movement() {
    let mut term = Vt100Backend::new(80, 24, 0).unwrap();
    term.process(b"Line 1\nLine 2");
    let cursor = term.cursor();
    assert_eq!(cursor.row, 1);
}

#[test]
fn test_resize() {
    let mut term = Vt100Backend::new(80, 24, 0).unwrap();
    term.resize(40, 12);
    let snap = term.screen_snapshot();
    assert_eq!(snap.cols, 40);
    assert_eq!(snap.num_rows, 12);
}

Red Flags — STOP and Rethink

• Modifying TerminalBackend trait — This affects BOTH backends. Test both paths.
• Ignoring the feature flag boundary — Code guarded by #[cfg(feature = "ghostty-backend")] must never reference vt100 and vice versa.
• Blocking reads on PTY — Always use AsyncPtyReader. Blocking the tokio runtime freezes the entire TUI.
• Skipping color mapping for a cell attribute — Missing bold/italic mapping makes harness TUIs look wrong.

Checklist Before Committing

• cargo check passes with default features (ghostty)
• cargo check --no-default-features --features vt100-backend passes (vt100 fallback path)
• Terminal emulation tests pass: cargo test -p hom-terminal
• PTY tests pass: cargo test -p hom-pty
• Color mapping covers all TermColor variants
• No blocking I/O on the tokio runtime
• Feature flag boundaries are clean (no cross-contamination)