panasyn 0.1.0

A lightweight GPU-accelerated terminal emulator for macOS and Linux.
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# PTY & ANSI

## Input / output pipeline

```
  Keyboard (winit KeyEvent)
       │
       ▼
  input::keyboard::key_to_bytes()
       │  ModifiersState tracked via WindowEvent::ModifiersChanged
       ▼
  pty::Session::write(&[u8])
       │  Blocking write with partial-write retry loop
       ▼
  PTY master fd
       │
       ▼
  Shell (zsh) running in PTY slave
       │  Processes input, produces output + escape sequences
       ▼
  PTY master fd
       │  Non-blocking poll + read in reader thread
       ▼
  EventLoopProxy::send_event(UserEvent::PtyOutput(data))
       │
       ▼ (main thread event loop)
  ansi::Parser::advance(&[u8], &mut Grid)
       │  vte::Parser state machine → vte::Perform callbacks
       │  - print(c)     → grid.put_char(c)
       │  - execute(c)   → \n, \r, \b, \t, \x0c
       │  - csi/esc/osc → ignored (no printed garbage)
       ▼
  Grid::to_string() → Renderer::draw()
       │
       ▼
  wgpu swap chain → Metal → Screen
```

## PTY

- Uses `nix::pty::forkpty` to create a pseudoterminal pair
- Child process exec's `$SHELL` (default: `zsh`)
- `Winsize` set on spawn; `TIOCSWINSZ` + `SIGWINCH` on resize
- **Reader thread**: polls master fd via `nix::poll` (100 ms timeout), sends data to main thread via `winit::EventLoopProxy`
- **Write loop**: handles partial writes (POSIX can return short count)
- **Write method** returns `usize` (bytes written) for instrumentation

## ANSI parser

Uses the `vte` crate (state machine used by Alacritty, Kitty) to correctly parse
VT escape sequences:

| `vte::Perform` method | What it handles | Current action |
|---|---|---|
| `print(c)` | Printable characters | `grid.put_char(c)` |
| `execute(byte)` | C0 control codes | `\n`→newline, `\r`→CR, `\b`→BS, `\t`→tab, `\x0c`→clear |
| `hook/put/unhook` | DCS (Device Control Strings) | Ignored |
| `osc_dispatch` | OSC (Operating System Commands) | Ignored |
| `csi_dispatch` | CSI (Control Sequence Introducer) | Ignored — M3 |
| `esc_dispatch` | ESC sequences | Ignored — M2+ |

CSI sequences (`ESC[`) and OSC sequences (`ESC]`) are **absorbed without printing**,
so escape sequence garbage no longer appears in the terminal.

## Future work (Milestones 2–3)

- SGR colors and text attributes (bold, italic, underline)
- Cursor positioning (CUP, CUU, CUD, CUF, CUB)
- Erase in display/line (ED, EL)
- Alternate screen buffer
- Scrollback ring buffer
- Device Control Strings for clipboard, hyperlinks, etc.