fix: gateway systemd unit now retries indefinitely with backoff (#18639)

The old defaults (StartLimitIntervalSec=600, StartLimitBurst=5,
RestartSec=30) meant any network outage over ~5 minutes would
permanently kill the gateway until manual intervention.

Changes:
- StartLimitIntervalSec=0 (never give up)
- Restart=always (not just on-failure)
- RestartSec=60 with RestartMaxDelaySec=300, RestartSteps=5
  (exponential backoff: 60 → 120 → 180 → 240 → 300s cap)
- After=network-online.target + Wants= (both units now wait for
  actual connectivity, not just network.target)

Power outage → internet down → internet back = auto-recovery.

hermes_cli/gateway.py

@@ -188,7 +188,7 @@ def _graceful_restart_via_sigusr1(pid: int, drain_timeout: float) -> bool:
 
     SIGUSR1 is wired in gateway/run.py to ``request_restart(via_service=True)``
     which drains in-flight agent runs (up to ``agent.restart_drain_timeout``
-    seconds), then exits with code 75.  Both systemd (``Restart=on-failure``
+    seconds), then exits with code 75.  Both systemd (``Restart=always``
     + ``RestartForceExitStatus=75``) and launchd (``KeepAlive.SuccessfulExit
     = false``) relaunch the process after the graceful exit.
 
@@ -1655,8 +1655,7 @@ def generate_systemd_unit(system: bool = False, run_as_user: str | None = None)
 Description={SERVICE_DESCRIPTION}
 After=network-online.target
 Wants=network-online.target
-StartLimitIntervalSec=600
-StartLimitBurst=5
+StartLimitIntervalSec=0
 
 [Service]
 Type=simple
@@ -1670,8 +1669,10 @@ Environment="LOGNAME={username}"
 Environment="PATH={sane_path}"
 Environment="VIRTUAL_ENV={venv_dir}"
 Environment="HERMES_HOME={hermes_home}"
-Restart=on-failure
-RestartSec=30
+Restart=always
+RestartSec=60
+RestartMaxDelaySec=300
+RestartSteps=5
 RestartForceExitStatus={GATEWAY_SERVICE_RESTART_EXIT_CODE}
 KillMode=mixed
 KillSignal=SIGTERM
@@ -1691,9 +1692,9 @@ WantedBy=multi-user.target
     sane_path = ":".join(path_entries)
     return f"""[Unit]
 Description={SERVICE_DESCRIPTION}
-After=network.target
-StartLimitIntervalSec=600
-StartLimitBurst=5
+After=network-online.target
+Wants=network-online.target
+StartLimitIntervalSec=0
 
 [Service]
 Type=simple
@@ -1702,8 +1703,10 @@ WorkingDirectory={working_dir}
 Environment="PATH={sane_path}"
 Environment="VIRTUAL_ENV={venv_dir}"
 Environment="HERMES_HOME={hermes_home}"
-Restart=on-failure
-RestartSec=30
+Restart=always
+RestartSec=60
+RestartMaxDelaySec=300
+RestartSteps=5
 RestartForceExitStatus={GATEWAY_SERVICE_RESTART_EXIT_CODE}
 KillMode=mixed
 KillSignal=SIGTERM
@@ -2451,7 +2454,7 @@ def run_gateway(verbose: int = 0, quiet: bool = False, replace: bool = False):
     print()
     
     # Exit with code 1 if gateway fails to connect any platform,
-    # so systemd Restart=on-failure will retry on transient errors
+    # so systemd Restart=always will retry on transient errors
     verbosity = None if quiet else verbose
     try:
         success = asyncio.run(start_gateway(replace=replace, verbosity=verbosity))