fix(gateway): remap HERMES_HOME to target user in system service unit

When `sudo hermes gateway install --system --run-as-user <user>` generates
the systemd unit, get_hermes_home() resolves to /root/.hermes because
Path.home() returns root's home under sudo. The unit correctly sets
HOME= and User= via _system_service_identity(), but HERMES_HOME was
computed independently and pointed to root's config directory.

Add _hermes_home_for_target_user() which remaps the current HERMES_HOME
to the equivalent path under the target user's home. This handles:
- Default ~/.hermes → target user's ~/.hermes
- Profiles (e.g. ~/.hermes/profiles/coder) → preserves relative structure
- Custom paths (e.g. /opt/hermes) → kept as-is

Supersedes #3861 which only handled the default case and left profiles
broken (also flagged by Copilot review).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hermes_cli/gateway.py

@@ -463,6 +463,32 @@ def _build_user_local_paths(home: Path, path_entries: list[str]) -> list[str]:
     return [p for p in candidates if p not in path_entries and Path(p).exists()]
 
 
+def _hermes_home_for_target_user(target_home_dir: str) -> str:
+    """Remap the current HERMES_HOME to the equivalent under a target user's home.
+
+    When installing a system service via sudo, get_hermes_home() resolves to
+    root's home.  This translates it to the target user's equivalent path:
+      /root/.hermes                    → /home/alice/.hermes
+      /root/.hermes/profiles/coder     → /home/alice/.hermes/profiles/coder
+      /opt/custom-hermes               → /opt/custom-hermes  (kept as-is)
+    """
+    current_hermes = get_hermes_home().resolve()
+    current_default = (Path.home() / ".hermes").resolve()
+    target_default = Path(target_home_dir) / ".hermes"
+
+    # Default ~/.hermes → remap to target user's default
+    if current_hermes == current_default:
+        return str(target_default)
+
+    # Profile or subdir of ~/.hermes → preserve the relative structure
+    try:
+        relative = current_hermes.relative_to(current_default)
+        return str(target_default / relative)
+    except ValueError:
+        # Completely custom path (not under ~/.hermes) — keep as-is
+        return str(current_hermes)
+
+
 def generate_systemd_unit(system: bool = False, run_as_user: str | None = None) -> str:
     python_path = get_python_path()
     working_dir = str(PROJECT_ROOT)
@@ -478,12 +504,11 @@ def generate_systemd_unit(system: bool = False, run_as_user: str | None = None)
         if resolved_node_dir not in path_entries:
             path_entries.append(resolved_node_dir)
 
-    hermes_home = str(get_hermes_home().resolve())
-
     common_bin_paths = ["/usr/local/sbin", "/usr/local/bin", "/usr/sbin", "/usr/bin", "/sbin", "/bin"]
 
     if system:
         username, group_name, home_dir = _system_service_identity(run_as_user)
+        hermes_home = _hermes_home_for_target_user(home_dir)
         path_entries.extend(_build_user_local_paths(Path(home_dir), path_entries))
         path_entries.extend(common_bin_paths)
         sane_path = ":".join(path_entries)
@@ -518,6 +543,7 @@ StandardError=journal
 WantedBy=multi-user.target
 """
 
+    hermes_home = str(get_hermes_home().resolve())
     path_entries.extend(_build_user_local_paths(Path.home(), path_entries))
     path_entries.extend(common_bin_paths)
     sane_path = ":".join(path_entries)