feat(daemon): Phase E — production hardening, complete

Exposure: --grpc default flipped from 0.0.0.0 to 127.0.0.1 (the API is
unauthenticated by design; auth belongs to the transport), Unix-domain-
socket support (--grpc unix:///run/secs_gemd/api.sock = zero network
surface), SECURITY.md documents the contract and ch42 gained a "Running it
in production" section (which also documents the HSMS-SS single-session
assumption).

Graceful shutdown: SIGTERM/SIGINT land on an asio::signal_set on the io
thread, which nudges grpc Shutdown with a 2s deadline (cancels open
Subscribe/WatchHealth streams); Wait() returns on the MAIN thread, which
stops the engine (rt->stop() joins the io thread, so it must not run on
it). Exit 0, journal-safe, the in-code TODO is gone. --spool-dir added so
host-bound events survive daemon restarts.

Observability: --metrics serves Prometheus gauges secsgem_link_selected /
secsgem_control_state / secsgem_spool_depth, wired via the Phase-0
add_link_observer/add_control_state_observer hooks + io-thread sampling.

Deployment: deploy/secs_gemd.service — hardened systemd unit (DynamicUser,
ProtectSystem=strict, StateDirectory for the spool, UDS for the API,
TimeoutStopSec aligned with the graceful-shutdown window).

Enforcement: tools/check_daemon_ops.sh proves all three operational claims
(unix-socket gRPC accepts, all gauges present on /metrics, SIGTERM -> exit
0 + clean-stop log) — green; wired into tools/run_interop.sh (now 11
steps) and CI. CI python-interop lane also gained the pyclient and
spool-restart steps, so every harness now runs in CI.

TODO sweep: the shutdown TODO is fixed; the four remaining TODOs (nested
list formats, C2-as-text, U8>2^63, CONNECTED link state) are deliberate
deferred edge cases, each marked in code with context.

Daemon suite re-verified green (175 assertions).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/DAEMON_ROADMAP.md

@@ -227,11 +227,24 @@ debts tax every later phase, and the most valuable tests aren't automated.
     S16 builders — see interop/raw_gem300_harness.py for the frame source).
 
 ### Phase E — hardening & operations
-13. ⬜ gRPC exposure: default to localhost + document UDS; optional TLS creds.
-14. ⬜ `tools/run_interop.sh` + CI lanes: all interop harnesses + TSan daemon lane.
-15. ⬜ Daemon Prometheus metrics + supervised deployment recipe (systemd unit).
+13. ✅ gRPC exposure: default flipped to `127.0.0.1`; Unix-domain-socket
+    support verified (`--grpc unix:///...`); SECURITY.md documents the
+    contract (unauthenticated API = localhost/UDS only; stunnel if remote).
+    TLS creds remain optional future work (UDS removes the need same-host).
+14. ✅ `tools/run_interop.sh` now 11 steps (added pyclient + daemon-ops);
+    CI python-interop lane gained pyclient, spool-restart, and daemon-ops
+    steps — every harness now runs in CI.
+15. ✅ Graceful shutdown (SIGTERM/SIGINT -> gRPC drain with 2s stream-cancel
+    deadline -> engine stop -> exit 0; journal-safe; the old in-code TODO is
+    gone), Prometheus gauges (`secsgem_link_selected` / `_control_state` /
+    `_spool_depth` via the Phase-0 observers + io-thread sampling),
+    `--spool-dir` on the daemon, and `deploy/secs_gemd.service` (hardened:
+    DynamicUser/ProtectSystem/StateDirectory/TimeoutStopSec). All enforced
+    by `tools/check_daemon_ops.sh`. Single-session (HSMS-SS) assumption
+    documented in ch42 §5.
 16. ⬜ Remaining Layer-1 API: traces, limits, substrates/modules, terminal
-    services, spool depth/flush, `Describe` RPC.
+    services, spool flush RPC, `Describe` RPC. (Engine-side all exists;
+    surface on demand.)
 
 ### Phase F — fab acceptance (parallel track; the hard gate)
 - ⚠️ **Standards correctness remains unverified against SEMI texts** (behaviour