feat(hindsight): configurable embedded daemon health grace timeout (#50341)

On resource-contended hosts the embedded Hindsight daemon can exceed a
single 2s /health check; upstream then waits a grace window before
treating it as stale and killing+restarting it (hindsight-embed reads
HINDSIGHT_EMBED_PORT_HEALTH_GRACE_TIMEOUT, default 30s, into a
module-level constant at import time). Users on busy boxes had no
Hermes-side way to raise it short of hand-setting an env var.

Add a 'port_health_grace_timeout' config.json option to the Hindsight
plugin. When set, initialize() exports it to the process env BEFORE
daemon_embed_manager is imported (the import-time read is the contract).
setdefault() so an explicit operator env override always wins. Exposed
in 'hermes memory setup' for local_embedded mode.

Follow-up to #50308 / issue #13125 comment thread.

tests/plugins/test_hindsight_health_grace_timeout.py

@@ -0,0 +1,64 @@
+"""Embedded-daemon health grace timeout export (issue #13125 comment thread).
+
+On resource-contended hosts the embedded Hindsight daemon can exceed a single
+2s /health check and get needlessly killed + restarted. Upstream exposes the
+grace window via HINDSIGHT_EMBED_PORT_HEALTH_GRACE_TIMEOUT (read at import
+time). The plugin surfaces it as a config.json knob and exports it to the
+process env BEFORE daemon_embed_manager is imported.
+"""
+
+import importlib
+
+import pytest
+
+hindsight = importlib.import_module("plugins.memory.hindsight")
+_export = hindsight._export_port_health_grace_timeout
+_ENV = hindsight._PORT_HEALTH_GRACE_ENV
+
+
+@pytest.fixture(autouse=True)
+def _clear_env(monkeypatch):
+    monkeypatch.delenv(_ENV, raising=False)
+
+
+def test_configured_value_exported(monkeypatch):
+    _export({"port_health_grace_timeout": 60})
+    import os
+
+    assert float(os.environ[_ENV]) == 60.0
+
+
+def test_string_value_parsed(monkeypatch):
+    _export({"port_health_grace_timeout": "45"})
+    import os
+
+    assert float(os.environ[_ENV]) == 45.0
+
+
+def test_blank_and_missing_are_noops(monkeypatch):
+    import os
+
+    _export({})
+    assert _ENV not in os.environ
+    _export({"port_health_grace_timeout": ""})
+    assert _ENV not in os.environ
+    _export({"port_health_grace_timeout": None})
+    assert _ENV not in os.environ
+
+
+def test_invalid_and_negative_ignored(monkeypatch):
+    import os
+
+    _export({"port_health_grace_timeout": "not-a-number"})
+    assert _ENV not in os.environ
+    _export({"port_health_grace_timeout": -5})
+    assert _ENV not in os.environ
+
+
+def test_explicit_env_wins_over_config(monkeypatch):
+    import os
+
+    monkeypatch.setenv(_ENV, "99")
+    _export({"port_health_grace_timeout": 60})
+    # setdefault must not clobber an operator-set env override.
+    assert os.environ[_ENV] == "99"