fix(gateway): make ws keepalive and orphan-reap grace config-driven (#79635)

- New dashboard.ws_ping_interval / dashboard.ws_ping_timeout defaults
  (20.0/20.0) in DEFAULT_CONFIG; hermes_cli/web_server.py reads them for
  non-loopback binds. Loopback keeps ws_ping=None (event-loop stalls must
  never kill a healthy local connection).
- New dashboard.ws_orphan_reap_grace_s (20.0): tui_gateway/server.py's
  _WS_ORPHAN_REAP_GRACE_S now resolves from config via
  _resolve_ws_orphan_reap_grace(); the HERMES_TUI_WS_ORPHAN_REAP_GRACE_S
  env var is kept as an internal override for backward compat and wins
  when set.
- tests/test_ws_keepalive_config.py: real load_config against a temp
  HERMES_HOME yaml — defaults, propagation, deep-merge, env override,
  invalid-value fallback.

tests/test_ws_keepalive_config.py

@@ -0,0 +1,92 @@
+"""Config propagation tests for the WS keepalive + orphan-reap grace knobs (#79635)."""
+
+import textwrap
+
+import pytest
+
+
+@pytest.fixture()
+def _temp_home(tmp_path, monkeypatch):
+    home = tmp_path / "hermes-home"
+    home.mkdir()
+    monkeypatch.setenv("HERMES_HOME", str(home))
+    monkeypatch.delenv("HERMES_TUI_WS_ORPHAN_REAP_GRACE_S", raising=False)
+    return home
+
+
+def _write_config(home, body: str) -> None:
+    (home / "config.yaml").write_text(textwrap.dedent(body))
+
+
+def test_dashboard_ws_defaults_present(_temp_home):
+    from hermes_cli.config import load_config
+
+    _write_config(_temp_home, "model:\n  default: test-model\n")
+    cfg = load_config()
+    dash = cfg.get("dashboard") or {}
+    assert dash.get("ws_ping_interval") == 20.0
+    assert dash.get("ws_ping_timeout") == 20.0
+    assert dash.get("ws_orphan_reap_grace_s") == 20.0
+
+
+def test_dashboard_ws_values_propagate_from_yaml(_temp_home):
+    from hermes_cli.config import load_config
+
+    _write_config(
+        _temp_home,
+        """
+        dashboard:
+          ws_ping_interval: 45.5
+          ws_ping_timeout: 10
+          ws_orphan_reap_grace_s: 90
+        """,
+    )
+    cfg = load_config()
+    dash = cfg["dashboard"]
+    assert dash["ws_ping_interval"] == 45.5
+    assert dash["ws_ping_timeout"] == 10
+    assert dash["ws_orphan_reap_grace_s"] == 90
+    # Deep-merge: sibling defaults survive a partial user section.
+    assert dash.get("theme") == "default"
+
+
+def test_ws_orphan_reap_grace_reads_config(_temp_home):
+    from tui_gateway import server
+
+    _write_config(
+        _temp_home,
+        """
+        dashboard:
+          ws_orphan_reap_grace_s: 33
+        """,
+    )
+    assert server._resolve_ws_orphan_reap_grace() == 33.0
+
+
+def test_ws_orphan_reap_grace_env_var_overrides_config(_temp_home, monkeypatch):
+    from tui_gateway import server
+
+    _write_config(
+        _temp_home,
+        """
+        dashboard:
+          ws_orphan_reap_grace_s: 33
+        """,
+    )
+    monkeypatch.setenv("HERMES_TUI_WS_ORPHAN_REAP_GRACE_S", "7")
+    assert server._resolve_ws_orphan_reap_grace() == 7.0
+
+
+def test_ws_orphan_reap_grace_invalid_values_fall_back(_temp_home, monkeypatch):
+    from tui_gateway import server
+
+    _write_config(
+        _temp_home,
+        """
+        dashboard:
+          ws_orphan_reap_grace_s: not-a-number
+        """,
+    )
+    assert server._resolve_ws_orphan_reap_grace() == 20.0
+    monkeypatch.setenv("HERMES_TUI_WS_ORPHAN_REAP_GRACE_S", "-5")
+    assert server._resolve_ws_orphan_reap_grace() == 0.0