diff --git a/gateway/platforms/base.py b/gateway/platforms/base.py
index f91a83a503..aa0c83d128 100644
--- a/gateway/platforms/base.py
+++ b/gateway/platforms/base.py
@@ -1552,6 +1552,10 @@ def _docker_sandbox_dir_candidates(session_key: str = "") -> List[str]:
         from tools.environments.base import sanitize_task_id_for_path
     except Exception:
         return ["default"]
+    # Explicit trusted-profiles opt-in: one shared container identity.
+    shared = os.getenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "").strip()
+    if shared:
+        candidates.append(sanitize_task_id_for_path(f"shared:{shared}"))
     try:
         from hermes_cli.profiles import get_active_profile_name
 
diff --git a/tests/tools/test_shared_container_task_id.py b/tests/tools/test_shared_container_task_id.py
index cb1eeef644..7e5c8da224 100644
--- a/tests/tools/test_shared_container_task_id.py
+++ b/tests/tools/test_shared_container_task_id.py
@@ -253,3 +253,59 @@ def test_ssh_backend_keeps_session_scoping(monkeypatch):
         assert terminal_tool._resolve_container_task_id(None) == "session:sess-A"
     finally:
         clear_session_vars(tokens)
+
+
+# --- Trusted-profiles shared container opt-in (#84671) ------------------------
+
+
+def test_shared_key_unifies_profiles(monkeypatch):
+    from gateway.session_context import clear_session_vars, set_session_vars
+
+    _persistent_docker(monkeypatch)
+    monkeypatch.setenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "team/workspace")
+    tokens = set_session_vars(session_key="s1", profile="work")
+    try:
+        a = terminal_tool._resolve_container_task_id(None)
+    finally:
+        clear_session_vars(tokens)
+    tokens = set_session_vars(session_key="s2", profile="research")
+    try:
+        b = terminal_tool._resolve_container_task_id(None)
+    finally:
+        clear_session_vars(tokens)
+    assert a == b == "shared:team/workspace"
+
+
+def test_shared_key_applies_to_cli_no_session(monkeypatch):
+    # CLI (no session key) must land in the same shared container as gateway
+    # sessions, or the opt-in splits the container it exists to unify.
+    _persistent_docker(monkeypatch)
+    monkeypatch.setenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "team/workspace")
+    monkeypatch.delenv("HERMES_SESSION_KEY", raising=False)
+    assert terminal_tool._resolve_container_task_id(None) == "shared:team/workspace"
+
+
+def test_empty_shared_key_keeps_profile_scoping(monkeypatch):
+    from gateway.session_context import clear_session_vars, set_session_vars
+
+    _persistent_docker(monkeypatch)
+    monkeypatch.setenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "")
+    tokens = set_session_vars(session_key="s1", profile="work")
+    try:
+        assert terminal_tool._resolve_container_task_id(None) == "profile:work"
+    finally:
+        clear_session_vars(tokens)
+
+
+def test_shared_key_ignored_outside_persistent_docker(monkeypatch):
+    # The opt-in is a persistent-Docker concept only: SSH keeps session
+    # scoping even when the key is set.
+    from gateway.session_context import clear_session_vars, set_session_vars
+
+    monkeypatch.setenv("TERMINAL_ENV", "ssh")
+    monkeypatch.setenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "team/workspace")
+    tokens = set_session_vars(session_key="sess-A", profile="work")
+    try:
+        assert terminal_tool._resolve_container_task_id(None) == "session:sess-A"
+    finally:
+        clear_session_vars(tokens)
diff --git a/tools/terminal_tool.py b/tools/terminal_tool.py
index 532595ea70..3390f472ee 100644
--- a/tools/terminal_tool.py
+++ b/tools/terminal_tool.py
@@ -1513,11 +1513,25 @@ def _resolve_container_task_id(task_id: Optional[str]) -> str:
         # the default profile share the SAME container — CLI's historical key
         # IS the default profile's container.
         if _docker_persistent_profile_scoped():
+            # Explicit opt-in: trusted profiles configuring the same
+            # terminal.docker_shared_container_key share ONE container/cache
+            # slot (and sandbox dir) regardless of profile name (#84671).
+            shared = os.getenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "").strip()
+            if shared:
+                return f"shared:{shared}"
             profile = _current_session_profile() or "default"
             if profile == "default":
                 return "default"
             return f"profile:{profile}"
         return f"session:{session_key}"
+    # CLI/no-session path: honour the shared-container opt-in here too, or a
+    # CLI run of a keyed profile would land in "default" while its gateway
+    # sessions land in "shared:<key>" — splitting the very container the
+    # setting exists to unify.
+    if _docker_persistent_profile_scoped():
+        shared = os.getenv("TERMINAL_DOCKER_SHARED_CONTAINER_KEY", "").strip()
+        if shared:
+            return f"shared:{shared}"
     return "default"