fix: per-profile subprocess HOME isolation (#4426) (#7357)

Isolate system tool configs (git, ssh, gh, npm) per profile by injecting
a per-profile HOME into subprocess environments only.  The Python
process's own os.environ['HOME'] and Path.home() are never modified,
preserving all existing profile infrastructure.

Activation is directory-based: when {HERMES_HOME}/home/ exists on disk,
subprocesses see it as HOME.  The directory is created automatically for:
- Docker: entrypoint.sh bootstraps it inside the persistent volume
- Named profiles: added to _PROFILE_DIRS in profiles.py

Injection points (all three subprocess env builders):
- tools/environments/local.py _make_run_env() — foreground terminal
- tools/environments/local.py _sanitize_subprocess_env() — background procs
- tools/code_execution_tool.py child_env — execute_code sandbox

Single source of truth: hermes_constants.get_subprocess_home()

Closes #4426

hermes_constants.py

@@ -111,6 +111,32 @@ def display_hermes_home() -> str:
         return str(home)
 
 
+def get_subprocess_home() -> str | None:
+    """Return a per-profile HOME directory for subprocesses, or None.
+
+    When ``{HERMES_HOME}/home/`` exists on disk, subprocesses should use it
+    as ``HOME`` so system tools (git, ssh, gh, npm …) write their configs
+    inside the Hermes data directory instead of the OS-level ``/root`` or
+    ``~/``.  This provides:
+
+    * **Docker persistence** — tool configs land inside the persistent volume.
+    * **Profile isolation** — each profile gets its own git identity, SSH
+      keys, gh tokens, etc.
+
+    The Python process's own ``os.environ["HOME"]`` and ``Path.home()`` are
+    **never** modified — only subprocess environments should inject this value.
+    Activation is directory-based: if the ``home/`` subdirectory doesn't
+    exist, returns ``None`` and behavior is unchanged.
+    """
+    hermes_home = os.getenv("HERMES_HOME")
+    if not hermes_home:
+        return None
+    profile_home = os.path.join(hermes_home, "home")
+    if os.path.isdir(profile_home):
+        return profile_home
+    return None
+
+
 VALID_REASONING_EFFORTS = ("minimal", "low", "medium", "high", "xhigh")