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.

tests/hermes_cli/test_pty_bridge.py

@@ -0,0 +1,172 @@
+"""Unit tests for hermes_cli.pty_bridge — PTY spawning + byte forwarding.
+
+These tests drive the bridge with minimal POSIX processes (echo, env, sleep,
+printf) to verify it behaves like a PTY you can read/write/resize/close.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+import time
+
+import pytest
+
+pytest.importorskip("ptyprocess", reason="ptyprocess not installed")
+
+from hermes_cli.pty_bridge import PtyBridge, PtyUnavailableError
+
+
+skip_on_windows = pytest.mark.skipif(
+    sys.platform.startswith("win"), reason="PTY bridge is POSIX-only"
+)
+
+
+def _read_until(bridge: PtyBridge, needle: bytes, timeout: float = 5.0) -> bytes:
+    """Accumulate PTY output until we see `needle` or time out."""
+    deadline = time.monotonic() + timeout
+    buf = bytearray()
+    while time.monotonic() < deadline:
+        chunk = bridge.read(timeout=0.2)
+        if chunk is None:
+            break
+        buf.extend(chunk)
+        if needle in buf:
+            return bytes(buf)
+    return bytes(buf)
+
+
+@skip_on_windows
+class TestPtyBridgeSpawn:
+    def test_is_available_on_posix(self):
+        assert PtyBridge.is_available() is True
+
+    def test_spawn_returns_bridge_with_pid(self):
+        bridge = PtyBridge.spawn(["true"])
+        try:
+            assert bridge.pid > 0
+        finally:
+            bridge.close()
+
+    def test_spawn_raises_on_missing_argv0(self, tmp_path):
+        with pytest.raises((FileNotFoundError, OSError)):
+            PtyBridge.spawn([str(tmp_path / "definitely-not-a-real-binary")])
+
+
+@skip_on_windows
+class TestPtyBridgeIO:
+    def test_reads_child_stdout(self):
+        bridge = PtyBridge.spawn(["/bin/sh", "-c", "printf hermes-ok"])
+        try:
+            output = _read_until(bridge, b"hermes-ok")
+            assert b"hermes-ok" in output
+        finally:
+            bridge.close()
+
+    def test_write_sends_to_child_stdin(self):
+        # `cat` with no args echoes stdin back to stdout.  We write a line,
+        # read it back, then signal EOF to let cat exit cleanly.
+        bridge = PtyBridge.spawn(["/bin/cat"])
+        try:
+            bridge.write(b"hello-pty\n")
+            output = _read_until(bridge, b"hello-pty")
+            assert b"hello-pty" in output
+        finally:
+            bridge.close()
+
+    def test_read_returns_none_after_child_exits(self):
+        bridge = PtyBridge.spawn(["/bin/sh", "-c", "printf done"])
+        try:
+            _read_until(bridge, b"done")
+            # Give the child a beat to exit cleanly, then drain until EOF.
+            deadline = time.monotonic() + 3.0
+            while bridge.is_alive() and time.monotonic() < deadline:
+                bridge.read(timeout=0.1)
+            # Next reads after exit should return None (EOF), not raise.
+            got_none = False
+            for _ in range(10):
+                if bridge.read(timeout=0.1) is None:
+                    got_none = True
+                    break
+            assert got_none, "PtyBridge.read did not return None after child EOF"
+        finally:
+            bridge.close()
+
+
+@skip_on_windows
+class TestPtyBridgeResize:
+    def test_resize_updates_child_winsize(self):
+        # tput reads COLUMNS/LINES from the TTY ioctl (TIOCGWINSZ).
+        # Spawn a shell, resize, then ask tput for the dimensions.
+        bridge = PtyBridge.spawn(
+            ["/bin/sh", "-c", "sleep 0.1; tput cols; tput lines"],
+            cols=80,
+            rows=24,
+        )
+        try:
+            bridge.resize(cols=123, rows=45)
+            output = _read_until(bridge, b"45", timeout=5.0)
+            # tput prints just the numbers, one per line
+            assert b"123" in output
+            assert b"45" in output
+        finally:
+            bridge.close()
+
+
+@skip_on_windows
+class TestPtyBridgeClose:
+    def test_close_is_idempotent(self):
+        bridge = PtyBridge.spawn(["/bin/sh", "-c", "sleep 30"])
+        bridge.close()
+        bridge.close()  # must not raise
+        assert not bridge.is_alive()
+
+    def test_close_terminates_long_running_child(self):
+        bridge = PtyBridge.spawn(["/bin/sh", "-c", "sleep 30"])
+        pid = bridge.pid
+        bridge.close()
+        # Give the kernel a moment to reap
+        deadline = time.monotonic() + 3.0
+        reaped = False
+        while time.monotonic() < deadline:
+            try:
+                os.kill(pid, 0)
+                time.sleep(0.05)
+            except ProcessLookupError:
+                reaped = True
+                break
+        assert reaped, f"pid {pid} still running after close()"
+
+
+@skip_on_windows
+class TestPtyBridgeEnv:
+    def test_cwd_is_respected(self, tmp_path):
+        bridge = PtyBridge.spawn(
+            ["/bin/sh", "-c", "pwd"],
+            cwd=str(tmp_path),
+        )
+        try:
+            output = _read_until(bridge, str(tmp_path).encode())
+            assert str(tmp_path).encode() in output
+        finally:
+            bridge.close()
+
+    def test_env_is_forwarded(self):
+        bridge = PtyBridge.spawn(
+            ["/bin/sh", "-c", "printf %s \"$HERMES_PTY_TEST\""],
+            env={**os.environ, "HERMES_PTY_TEST": "pty-env-works"},
+        )
+        try:
+            output = _read_until(bridge, b"pty-env-works")
+            assert b"pty-env-works" in output
+        finally:
+            bridge.close()
+
+
+class TestPtyBridgeUnavailable:
+    """Platform fallback semantics — PtyUnavailableError is importable and
+    carries a user-readable message."""
+
+    def test_error_carries_user_message(self):
+        err = PtyUnavailableError("platform not supported")
+        assert "platform" in str(err)