Initial build: scrawl, a shared ASCII canvas over SSH

ssh in and draw on a live, shared doodle wall -- everyone connected
sees everyone else's edits in real time. Same wish+bubbletea security
model as delve-term (no shell, no exec, structurally can't reach a
real shell on the host), extended with the one thing delve-term didn't
need: multiple sessions sharing live state. wish's bm.Middleware helper
hides the *tea.Program it creates, so this builds the program directly
instead, keeping a registry (game.Canvas) that broadcasts a redraw
signal to every other connected session the instant one of them paints.

Banner generated via `figlet -f slant SCRAWL` rather than hand-drawn --
slant felt right for a doodle/scribble tool.

Two real bugs caught by actually running this with real SSH sessions,
not just unit-testing the game logic in isolation:

1. Program.Send() blocks until that program's Run() event loop is
   actively reading from it. Broadcasting synchronously from inside
   Join()/Paint() (including a session broadcasting to its own,
   not-yet-running program on join) deadlocked every session before it
   ever reached Run() -- the very first connection just hung with
   nothing rendered. Fixed by sending asynchronously (go p.Send(...))
   everywhere the canvas notifies sessions of a change.

2. Subtler: lipgloss's default package-level styles detect color
   support from the *server process's* os.Stdout, not any given
   session's actual terminal -- and a server's stdout is typically
   redirected (a log file, systemd journal), so every connected session
   silently lost all color/background styling at once, server-wide.
   Manifested as painting a cell your own cursor already sat on being
   invisible (the cursor glyph before/after looked identical, so
   bubbletea's diffing renderer correctly sent zero bytes for a change
   that produced no visual diff) -- confirmed via server-side debug
   logging that painting itself worked correctly every time, isolating
   the bug to rendering, then confirmed via a Go test that forcing a
   real color profile was the difference between 0 and 1327 runes of
   diff between two frames that should look different. Fixed with a
   lipgloss.Renderer created per-session, bound to that session's
   actual output, forced to TrueColor; cursors now highlight whatever's
   already painted at that cell (background tint) rather than
   replacing the character, so a session's own paint is never masked
   by its own cursor marker sitting on top of it.

Verified end-to-end with two real, simultaneous SSH sessions (scripted
via pexpect): peer count syncs correctly, and one session's paint
genuinely arrives at the other via the live broadcast -- not just
unit-tested in isolation. Also verified the actual Docker image builds
and serves correctly over real SSH.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

game/model.go

@@ -0,0 +1,95 @@
+package game
+
+import (
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/charmbracelet/lipgloss"
+)
+
+var inkPalette = []string{"#ff6b6b", "#feca57", "#1dd1a1", "#54a0ff", "#ff9ff3", "#48dbfb", "#f368e0", "#ffffff"}
+var charPalette = []rune{'█', '▓', '▒', '░', '#', '*', '.', '@', 'o', '+'}
+
+type state int
+
+const (
+	stateIntro state = iota
+	stateCanvas
+)
+
+type Model struct {
+	canvas   *Canvas
+	id       string
+	label    string
+	state    state
+	renderer *lipgloss.Renderer
+
+	inkColorIdx int
+	charIdx     int
+
+	width, height int
+}
+
+func NewModel(canvas *Canvas, id, label string, renderer *lipgloss.Renderer) Model {
+	return Model{canvas: canvas, id: id, label: label, state: stateIntro, renderer: renderer}
+}
+
+func (m Model) Init() tea.Cmd { return nil }
+
+func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.WindowSizeMsg:
+		m.width, m.height = msg.Width, msg.Height
+		return m, nil
+
+	case canvasUpdatedMsg:
+		// Someone (possibly this session) changed the shared state --
+		// nothing to do here but re-render; View() always reads a fresh
+		// snapshot from the canvas.
+		return m, nil
+
+	case tea.KeyMsg:
+		if m.state == stateIntro {
+			m.state = stateCanvas
+			return m, nil
+		}
+		return m.handleKey(msg)
+	}
+	return m, nil
+}
+
+func (m Model) handleKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
+	switch msg.String() {
+	case "ctrl+c", "q":
+		return m, tea.Quit
+
+	case "up", "k":
+		m.canvas.MoveCursor(m.id, 0, -1)
+	case "down", "j":
+		m.canvas.MoveCursor(m.id, 0, 1)
+	case "left", "h":
+		m.canvas.MoveCursor(m.id, -1, 0)
+	case "right", "l":
+		m.canvas.MoveCursor(m.id, 1, 0)
+
+	case " ", "enter":
+		if cur, ok := m.canvas.CursorsSnapshot()[m.id]; ok {
+			m.canvas.Paint(cur.X, cur.Y, charPalette[m.charIdx], inkPalette[m.inkColorIdx])
+		}
+
+	case "backspace", "delete":
+		if cur, ok := m.canvas.CursorsSnapshot()[m.id]; ok {
+			m.canvas.Paint(cur.X, cur.Y, ' ', "")
+		}
+
+	case "[":
+		m.charIdx = (m.charIdx - 1 + len(charPalette)) % len(charPalette)
+	case "]":
+		m.charIdx = (m.charIdx + 1) % len(charPalette)
+
+	case "1", "2", "3", "4", "5", "6", "7", "8":
+		m.inkColorIdx = int(msg.String()[0] - '1')
+
+	case "c":
+		m.canvas.Clear()
+	}
+	return m, nil
+}