feat: read-only Session Dashboard (agent-tty dashboard)

[ThomasK33]

What

Adds agent-tty dashboard: a read-only, interactive Session Dashboard — a master-detail Ink TUI that lists your Sessions and shows a continuously-updated Live View of the selected one. Watch what your agents are doing in their shells, e.g. in a tmux split.

The Live View is produced by Event Log Follow: it tails the Session's append-only events.jsonl and replays it through the in-process libghostty-vt renderer (replayTo → snapshot). It reads the Event Log as the source of truth and never queries the live host, so it can't disturb a running Session and behaves identically for live and finished Sessions (ADR 0006).

Closes #109.

Highlights

• Master-detail with a Tab-toggled focus model: list focused → ↑/↓ j/k select; Live View focused → ↑/↓ h/j/k/l pan.
• Scope: defaults to Active Sessions (mirrors list); a toggles all (Active + Terminal, excluding destroyed); --all sets the initial scope; --session <id> preselects.
• Sizing: 1:1 clip-top-left + pan + truncation indicators, letterbox for smaller screens, and a lossy block-glyph overview (z). Never distorts/reflows; never resizes the Session.
• Lifecycle: pin-selected-through-exit (final screen frozen + exit badge); a collected Event Log surfaces “Event Log collected” and drops on the next refresh.
• Renderer: requires the optional libghostty-vt (no ghostty-web fallback). Fails fast with an actionable message when absent, and doctor now reports a dashboard readiness capability.
• Interactive-only: no --json (a deliberate, documented deviation — list --json still covers machine-readable listing); fails fast on a non-interactive terminal.

Four deep modules (unit-tested)

• SessionEventSource + EventLogTailSource — byte-offset tail seam: partial lines, multibyte split, truncation/rewrite, not-yet-created vs collected, ENOENT offset reset.
• LiveViewProjection — pure clip / pan (clamped) / letterbox / block-glyph overview, cursor flag, cells-or-text fallback.
• LiveViewFollower — accumulate → replayTo → snapshot, burst coalescing, pin-on-exit freeze + badge, collected precedence, bounded replay (trims applied events).
• RendererReadiness — libghostty-vt probe → actionable error + the dashboard doctor capability (skips, not fails, when the optional renderer is absent).

Thin glue: session-list scope adapter (reuses listSessions), the Ink shell, and the dashboard CLI command + non-TTY guard.

Build / deps

react + ink moved to dependencies; @types/react added as a devDep; jsx: react-jsx added to tsconfig. @coder/libghostty-vt-node remains an optional dependency. The gitignored throwaway proto/ is removed.

Verification

• Byte-identical to agent-tty snapshot (cells, visibleLines, cursor, alt-screen) via a hermetic event-log cross-check.
• Live PTY run: boots, lists sessions, renders the Live View with the exit badge + clip indicator, overview block glyphs, focus/keys, and a clean quit.
• Gates: format, lint, typecheck, 1190 unit tests, and build — all green. (Integration/e2e create live hosts, so they run in CI rather than locally.)
• A 9-angle review pass (with adversarial verification) surfaced and fixed 6 issues in the new code: unhandled-rejection resilience (including the dispose-mid-render teardown race), pan clamping, bounded events array, list scroll window, refresh in-flight guard, and the ENOENT offset reset.

Out of scope / follow-up

Input take-over, multi-session grid, busy/idle activity, scrollback/replay-scrubbing, a streaming subscribe RPC, and pixel zoom are deliberately deferred (see the PRD). Wide-character (CJK/emoji) cell alignment is a pre-existing limitation of the shared SnapshotCell representation (the dashboard still matches snapshot) — tracked in #112.

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