docs: document the dashboard Chat tab

AGENTS.md — new subsection under TUI Architecture explaining that the
dashboard embeds the real hermes --tui rather than rewriting it,
with pointers to the pty_bridge + WebSocket endpoint and the rule
'never add a parallel chat surface in React.'

website/docs/user-guide/features/web-dashboard.md — user-facing Chat
section inside the existing Web Dashboard page, covering how it works
(WebSocket + PTY + xterm.js), the Sessions-page resume flow, and
prerequisites (Node.js, ptyprocess, POSIX kernel / WSL on Windows).

AGENTS.md

@@ -243,6 +243,17 @@ npm run fmt       # prettier
 npm test          # vitest
 ```
 
+### TUI in the Dashboard (`hermes dashboard` → `/chat`)
+
+The dashboard embeds the real `hermes --tui` — **not** a rewrite.  See `hermes_cli/pty_bridge.py` + the `@app.websocket("/api/pty")` endpoint in `hermes_cli/web_server.py`.
+
+- Browser loads `web/src/pages/ChatPage.tsx`, which mounts xterm.js's `Terminal` with the WebGL renderer, `@xterm/addon-fit` for container-driven resize, and `@xterm/addon-unicode11` for modern wide-character widths.
+- `/api/pty?token=…` upgrades to a WebSocket; auth uses the same ephemeral `_SESSION_TOKEN` as REST, via query param (browsers can't set `Authorization` on WS upgrade).
+- The server spawns whatever `hermes --tui` would spawn, through `ptyprocess` (POSIX PTY — WSL works, native Windows does not).
+- Frames: raw PTY bytes each direction; resize via `\x1b[RESIZE:<cols>;<rows>]` intercepted on the server and applied with `TIOCSWINSZ`.
+
+**Never add a parallel chat surface in React.** If you catch yourself re-implementing slash popover / model picker / tool cards for the dashboard, stop — the TUI already does those, and anything new you add to Ink will appear in the dashboard automatically.
+
 ---
 
 ## Adding New Tools

website/docs/user-guide/features/web-dashboard.md

@@ -60,6 +60,28 @@ The landing page shows a live overview of your installation:
 
 The status page auto-refreshes every 5 seconds.
 
+### Chat
+
+The **Chat** tab embeds the full Hermes TUI (the same interface you get from `hermes --tui`) directly in the browser. Everything you can do in the terminal TUI — slash commands, model picker, tool-call cards, markdown streaming, clarify/sudo/approval prompts, skin theming — works identically here, because the dashboard is running the real TUI binary and rendering its ANSI output through [xterm.js](https://xtermjs.org/) with its WebGL renderer for pixel-perfect cell layout.
+
+**How it works:**
+
+- `/api/pty` opens a WebSocket authenticated with the dashboard's session token
+- The server spawns `hermes --tui` behind a POSIX pseudo-terminal
+- Keystrokes travel to the PTY; ANSI output streams back to the browser
+- xterm.js's WebGL renderer paints each cell to an integer-pixel grid; mouse tracking (SGR 1006), wide characters (Unicode 11), and box-drawing glyphs all render natively
+- Resizing the browser window resizes the TUI via the `@xterm/addon-fit` addon
+
+**Resume an existing session:** from the **Sessions** tab, click the play icon (▶) next to any session. That jumps to `/chat?resume=<id>` and launches the TUI with `--resume`, loading the full history.
+
+**Prerequisites:**
+
+- Node.js (same requirement as `hermes --tui`; the TUI bundle is built on first launch)
+- `ptyprocess` — included when you `pip install hermes-agent[web]`
+- POSIX kernel (Linux, macOS, or WSL). Native Windows Python is not supported — use WSL.
+
+Close the browser tab and the PTY is reaped cleanly on the server. Re-opening spawns a fresh session.
+
 ### Config
 
 A form-based editor for `config.yaml`. All 150+ configuration fields are auto-discovered from `DEFAULT_CONFIG` and organized into tabbed categories: