feat(web): add /api/pty WebSocket bridge to embed TUI in dashboard

Exposes hermes --tui over a PTY-backed WebSocket so the dashboard can
embed the real TUI rather than reimplement its surface. The browser
attaches xterm.js to the socket; keystrokes flow in, PTY output bytes
flow out.

Architecture:

    browser <Terminal> (xterm.js)
           │  onData ───► ws.send(keystrokes)
           │  onResize ► ws.send('\x1b[RESIZE:cols;rows]')
           │  write   ◄── ws.onmessage (PTY bytes)
           ▼
    FastAPI /api/pty (token-gated, loopback-only)
           ▼
    PtyBridge (ptyprocess) ── spawns node ui-tui/dist/entry.js ──► tui_gateway + AIAgent

Components
----------

hermes_cli/pty_bridge.py
  Thin wrapper around ptyprocess.PtyProcess: byte-safe read/write on the
  master fd via os.read/os.write (not PtyProcessUnicode — ANSI is
  inherently byte-oriented and UTF-8 boundaries may land mid-read),
  non-blocking select-based reads, TIOCSWINSZ resize, idempotent
  SIGHUP→SIGTERM→SIGKILL teardown, platform guard (POSIX-only; Windows
  is WSL-supported only).

hermes_cli/web_server.py
  @app.websocket("/api/pty") endpoint gated by the existing
  _SESSION_TOKEN (via ?token= query param since browsers can't set
  Authorization on WS upgrades). Loopback-only enforcement. Reader task
  uses run_in_executor to pump PTY bytes without blocking the event
  loop. Writer loop intercepts a custom \x1b[RESIZE:cols;rows] escape
  before forwarding to the PTY. The endpoint resolves the TUI argv
  through a _resolve_chat_argv hook so tests can inject fake commands
  without building the real TUI.

Tests
-----

tests/hermes_cli/test_pty_bridge.py — 12 unit tests: spawn, stdout,
stdin round-trip, EOF, resize (via TIOCSWINSZ + tput readback), close
idempotency, cwd, env forwarding, unavailable-platform error.

tests/hermes_cli/test_web_server.py — TestPtyWebSocket adds 7 tests:
missing/bad token rejection (close code 4401), stdout streaming,
stdin round-trip, resize escape forwarding, unavailable-platform ANSI
error frame + 1011 close, resume parameter forwarding to argv.

96 tests pass under scripts/run_tests.sh.

hermes_cli/web_server.py

@@ -48,7 +48,7 @@ from hermes_cli.config import (
 from gateway.status import get_running_pid, read_runtime_status
 
 try:
-    from fastapi import FastAPI, HTTPException, Request
+    from fastapi import FastAPI, HTTPException, Request, WebSocket, WebSocketDisconnect
     from fastapi.middleware.cors import CORSMiddleware
     from fastapi.responses import FileResponse, HTMLResponse, JSONResponse
     from fastapi.staticfiles import StaticFiles
@@ -2021,6 +2021,148 @@ async def get_usage_analytics(days: int = 30):
         db.close()
 
 
+# ---------------------------------------------------------------------------
+# /api/pty — PTY-over-WebSocket bridge for the dashboard "Chat" tab.
+#
+# The endpoint spawns the same ``hermes --tui`` binary the CLI uses, behind
+# a POSIX pseudo-terminal, and forwards bytes + resize escapes across a
+# WebSocket.  The browser renders the ANSI through xterm.js (see
+# web/src/pages/ChatPage.tsx).
+#
+# Auth: ``?token=<session_token>`` query param (browsers can't set
+# Authorization on the WS upgrade).  Same ephemeral ``_SESSION_TOKEN`` as
+# REST.  Localhost-only — we defensively reject non-loopback clients even
+# though uvicorn binds to 127.0.0.1.
+# ---------------------------------------------------------------------------
+
+import re
+import asyncio
+
+from hermes_cli.pty_bridge import PtyBridge, PtyUnavailableError
+
+_RESIZE_RE = re.compile(rb"\x1b\[RESIZE:(\d+);(\d+)\]")
+_PTY_READ_CHUNK_TIMEOUT = 0.2
+# Starlette's TestClient reports the peer as "testclient"; treat it as
+# loopback so tests don't need to rewrite request scope.
+_LOOPBACK_HOSTS = frozenset({"127.0.0.1", "::1", "localhost", "testclient"})
+
+
+def _resolve_chat_argv(
+    resume: Optional[str] = None,
+) -> tuple[list[str], Optional[str], Optional[dict]]:
+    """Resolve the argv + cwd + env for the chat PTY.
+
+    Default: whatever ``hermes --tui`` would run.  Tests monkeypatch this
+    function to inject a tiny fake command (``cat``, ``sh -c 'printf …'``)
+    so nothing has to build Node or the TUI bundle.
+
+    Session resume is propagated via the ``HERMES_TUI_RESUME`` env var —
+    matching what ``hermes_cli.main._launch_tui`` does for the CLI path.
+    Appending ``--resume <id>`` to argv doesn't work because ``ui-tui`` does
+    not parse its argv.
+    """
+    from hermes_cli.main import PROJECT_ROOT, _make_tui_argv
+
+    argv, cwd = _make_tui_argv(PROJECT_ROOT / "ui-tui", tui_dev=False)
+    env: Optional[dict] = None
+    if resume:
+        env = os.environ.copy()
+        env["HERMES_TUI_RESUME"] = resume
+    return list(argv), str(cwd) if cwd else None, env
+
+
+@app.websocket("/api/pty")
+async def pty_ws(ws: WebSocket) -> None:
+    # --- auth + loopback check (before accept so we can close cleanly) ---
+    token = ws.query_params.get("token", "")
+    expected = _SESSION_TOKEN
+    if not hmac.compare_digest(token.encode(), expected.encode()):
+        await ws.close(code=4401)
+        return
+
+    client_host = ws.client.host if ws.client else ""
+    if client_host and client_host not in _LOOPBACK_HOSTS:
+        await ws.close(code=4403)
+        return
+
+    await ws.accept()
+
+    # --- spawn PTY ------------------------------------------------------
+    resume = ws.query_params.get("resume") or None
+    try:
+        argv, cwd, env = _resolve_chat_argv(resume=resume)
+    except SystemExit as exc:
+        # _make_tui_argv calls sys.exit(1) when node/npm is missing.
+        await ws.send_text(f"\r\n\x1b[31mChat unavailable: {exc}\x1b[0m\r\n")
+        await ws.close(code=1011)
+        return
+
+
+    try:
+        bridge = PtyBridge.spawn(argv, cwd=cwd, env=env)
+    except PtyUnavailableError as exc:
+        await ws.send_text(f"\r\n\x1b[31mChat unavailable: {exc}\x1b[0m\r\n")
+        await ws.close(code=1011)
+        return
+    except (FileNotFoundError, OSError) as exc:
+        await ws.send_text(f"\r\n\x1b[31mChat failed to start: {exc}\x1b[0m\r\n")
+        await ws.close(code=1011)
+        return
+
+    loop = asyncio.get_running_loop()
+
+    # --- reader task: PTY master → WebSocket ----------------------------
+    async def pump_pty_to_ws() -> None:
+        while True:
+            chunk = await loop.run_in_executor(
+                None, bridge.read, _PTY_READ_CHUNK_TIMEOUT
+            )
+            if chunk is None:  # EOF
+                return
+            if not chunk:  # no data this tick; yield control and retry
+                await asyncio.sleep(0)
+                continue
+            try:
+                await ws.send_bytes(chunk)
+            except Exception:
+                return
+
+    reader_task = asyncio.create_task(pump_pty_to_ws())
+
+    # --- writer loop: WebSocket → PTY master ----------------------------
+    try:
+        while True:
+            msg = await ws.receive()
+            msg_type = msg.get("type")
+            if msg_type == "websocket.disconnect":
+                break
+            raw = msg.get("bytes")
+            if raw is None:
+                text = msg.get("text")
+                raw = text.encode("utf-8") if isinstance(text, str) else b""
+            if not raw:
+                continue
+
+            # Resize escape is consumed locally, never written to the PTY.
+            match = _RESIZE_RE.match(raw)
+            if match and match.end() == len(raw):
+                cols = int(match.group(1))
+                rows = int(match.group(2))
+                bridge.resize(cols=cols, rows=rows)
+                continue
+
+            bridge.write(raw)
+    except WebSocketDisconnect:
+        pass
+    finally:
+        reader_task.cancel()
+        try:
+            await reader_task
+        except (asyncio.CancelledError, Exception):
+            pass
+        bridge.close()
+
+
 def mount_spa(application: FastAPI):
     """Mount the built SPA. Falls back to index.html for client-side routing.