diff --git a/pm/plugins_state.py b/pm/plugins_state.py
index a265c8befc..38e130ce86 100644
--- a/pm/plugins_state.py
+++ b/pm/plugins_state.py
@@ -14,10 +14,17 @@ from pathlib import Path
 
 
 def _profiles_root() -> Path:
-    # Profile operations are HOME-anchored by design (AGENTS.md rule 6:
-    # _get_profiles_root returns Path.home()/.hermes/profiles so every
-    # profile is visible regardless of which is active).
-    return Path.home() / ".hermes" / "profiles"
+    # Profile roots are derived from get_default_hermes_root() — the ONE
+    # authority for "where do profiles live" (hermes_constants): it
+    # returns HERMES_HOME directly for custom roots (Docker /opt/data,
+    # non-default local roots) and <root> for profile-mode HERMES_HOME,
+    # on both standard and custom layouts. Hardcoding Path.home()/
+    # .hermes/profiles silently omits custom-root profiles — their
+    # enabled dep plugins never join the union and bisect disable
+    # decisions never write back to their config.
+    from hermes_constants import get_default_hermes_root
+
+    return get_default_hermes_root() / "profiles"
 
 
 def _enabled_list_for_home(home: Path) -> list[str]:
diff --git a/pm/workspace.py b/pm/workspace.py
index b26cb8a041..1df2e25a40 100644
--- a/pm/workspace.py
+++ b/pm/workspace.py
@@ -77,10 +77,16 @@ def build_root(plugin_dirs: list[Path]) -> Path:
 
 
 def _plugin_dir_roots() -> set[Path]:
-    """All profile plugin dirs + the default home's, machine-wide."""
+    """All profile plugin dirs + the default home's, machine-wide.
+    Profile roots derive from get_default_hermes_root() — the ONE
+    authority (custom HERMES_HOME → that root directly; profile-mode
+    → its parent), so Docker/custom-root profiles join the union the
+    same as standard ones."""
     roots: set[Path] = set()
     try:
-        profiles_root = Path.home() / ".hermes" / "profiles"
+        from hermes_constants import get_default_hermes_root
+
+        profiles_root = get_default_hermes_root() / "profiles"
         if profiles_root.is_dir():
             for profile in profiles_root.iterdir():
                 if profile.is_dir():
diff --git a/tests/pm/test_custom_root_union.py b/tests/pm/test_custom_root_union.py
new file mode 100644
index 0000000000..5d10e6a5ae
--- /dev/null
+++ b/tests/pm/test_custom_root_union.py
@@ -0,0 +1,136 @@
+"""E2E: custom HERMES_HOME roots (Docker, non-default local) join the
+plugin-deps union the same as standard ~/.hermes ones.
+
+get_default_hermes_root() is the ONE authority: HERMES_HOME outside the
+default (e.g. /opt/data in Docker) → that root directly; profile-mode
+HERMES_HOME (<root>/profiles/<name>) → <root>. The union's profile scan
+and the bisect disable write-back must both flow through it — the bug
+this guards: hardcoded Path.home()/.hermes/profiles silently omitted
+custom-root profiles (enabled dep plugins never joined the union; disable
+decisions never wrote back).
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import yaml
+
+import pm.plugins_state as pstate
+import pm.workspace as ws
+
+
+def _write_enabled(home: Path, enabled: list) -> None:
+    home.mkdir(parents=True, exist_ok=True)
+    with (home / "config.yaml").open("w", encoding="utf-8") as f:
+        yaml.safe_dump({"plugins": {"enabled": enabled}}, f)
+
+
+def _make_dep_plugin(plugins_dir: Path, name: str) -> Path:
+    plug = plugins_dir / name
+    plug.mkdir(parents=True)
+    (plug / "plugin.yaml").write_text(f"name: {name}\n", encoding="utf-8")
+    (plug / "pyproject.toml").write_text(
+        "[project]\n"
+        f'name = "{name}"\n'
+        'version = "0.1.0"\n'
+        'requires-python = ">=3.11"\n'
+        'dependencies = ["pyfiglet==1.0.2"]\n',
+        encoding="utf-8",
+    )
+    return plug
+
+
+def test_custom_hermes_home_profile_joins_union(tmp_path, monkeypatch):
+    """Docker shape: HERMES_HOME=/opt/data-like root, a profile under it
+    with an enabled dep plugin. Discovery must find the member through
+    the REAL get_default_hermes_root (no path mocks)."""
+    custom_root = tmp_path / "opt-data"  # the /opt/data shape
+    profile_home = custom_root / "profiles" / "worker"
+    _write_enabled(profile_home, ["dep-plug"])
+    _make_dep_plugin(profile_home / "plugins", "dep-plug")
+
+    monkeypatch.setenv("HERMES_HOME", str(custom_root))
+    import hermes_constants
+
+    # the real authority must resolve the custom root (the contract this
+    # test exists to pin: env → get_default_hermes_root → union)
+    assert hermes_constants.get_default_hermes_root() == custom_root
+
+    # union discovery: the profile's enabled dep plugin IS a member
+    members = ws.enabled_member_dirs()
+    assert [p.name for p in members] == ["dep-plug"], (
+        "custom-root profile's enabled dep plugin missing from the union — "
+        "profile scan must derive from get_default_hermes_root"
+    )
+    # ordered enabled reads see it too
+    ordered = pstate.enabled_plugins_ordered()
+    assert ordered.get(profile_home / "plugins") == ["dep-plug"]
+
+
+def test_custom_hermes_home_disable_writes_back(tmp_path, monkeypatch):
+    """Bisect disable decisions must write back to the CUSTOM-root
+    profile's config — the resolver disabling a plugin there updates
+    that profile's enabled list."""
+    custom_root = tmp_path / "opt-data"
+    profile_home = custom_root / "profiles" / "worker"
+    _write_enabled(profile_home, ["bad-plug", "keep-plug"])
+    _make_dep_plugin(profile_home / "plugins", "bad-plug")
+    _make_dep_plugin(profile_home / "plugins", "keep-plug")
+
+    monkeypatch.setenv("HERMES_HOME", str(custom_root))
+
+    removed = pstate.disable_plugins(["bad-plug"])
+    assert removed[str(profile_home)] == ["bad-plug"]
+
+    # the profile's config reflects the removal
+    with (profile_home / "config.yaml").open(encoding="utf-8-sig") as f:
+        cfg = yaml.safe_load(f)
+    assert cfg["plugins"]["enabled"] == ["keep-plug"]
+
+    # and the union no longer sees the disabled member
+    members = ws.enabled_member_dirs()
+    assert [p.name for p in members] == ["keep-plug"]
+
+
+def test_standard_layout_still_works(tmp_path, monkeypatch):
+    """The default-home path: profile under the (monkeypatched) default
+    root, standard layout. Guards the derivation change didn't break the
+    common case."""
+    default_root = tmp_path / "home"  # stands in for ~/.hermes
+    profile_home = default_root / "profiles" / "coder"
+    _write_enabled(profile_home, ["dep-plug"])
+    _make_dep_plugin(profile_home / "plugins", "dep-plug")
+
+    import hermes_constants
+
+    monkeypatch.setattr(
+        hermes_constants, "get_default_hermes_root", lambda: default_root
+    )
+    # NOTE: pm.plugins_state imports the function lazily inside
+    # _profiles_root, so the attribute patch reaches it.
+
+    members = ws.enabled_member_dirs()
+    assert [p.name for p in members] == ["dep-plug"]
+
+
+def test_profile_mode_hermes_home_resolves_parent(tmp_path, monkeypatch):
+    """Profile-mode shape: HERMES_HOME=<root>/profiles/<name> — the
+    authority returns <root> so sibling profiles join the union."""
+    root = tmp_path / "data-root"
+    active_home = root / "profiles" / "active"
+    sibling_home = root / "profiles" / "sibling"
+    _write_enabled(sibling_home, ["dep-plug"])
+    _make_dep_plugin(sibling_home / "plugins", "dep-plug")
+    active_home.mkdir(parents=True)  # active profile has no dep plugins
+
+    monkeypatch.setenv("HERMES_HOME", str(active_home))
+    import hermes_constants
+
+    assert hermes_constants.get_default_hermes_root() == root
+
+    members = ws.enabled_member_dirs()
+    assert [p.name for p in members] == ["dep-plug"], (
+        "profile-mode HERMES_HOME must not hide sibling profiles' plugins "
+        "from the union"
+    )